AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 10 Transmission |
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<p>The following concepts are to be researched this week:</p>
<p>• <a href="http://www.google.com/custom?hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BLH%3A50%3BLW%3A300%3BGL%3A1%3BBGC%3AFFFFFF%3BT%3A%23000000%3BLC%3A%23000000%3BVLC%3A%23000000%3BALC%3A%23000000%3BGALT%3A%23000000%3BGFNT%3A%23999999%3BGIMP%3A%23999999%3BDIV%3A%23FF8400%3BLBGC%3AFF8400%3BAH%3Acenter%3BS%3Ahttp%3A%2F%2Fwww.audiocourses.com%3B&domains=audiocourses.com&q=digital%2Baudio%2BWire&btnG=Search&sitesearch=">Wire</a>
</p>
<p>• <a href="http://www.google.com/custom?hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BLH%3A50%3BLW%3A300%3BGL%3A1%3BBGC%3AFFFFFF%3BT%3A%23000000%3BLC%3A%23000000%3BVLC%3A%23000000%3BALC%3A%23000000%3BGALT%3A%23000000%3BGFNT%3A%23999999%3BGIMP%3A%23999999%3BDIV%3A%23FF8400%3BLBGC%3AFF8400%3BAH%3Acenter%3BS%3Ahttp%3A%2F%2Fwww.audiocourses.com%3B&domains=audiocourses.com&q=digital%2Baudio%2Btelephony&btnG=Search&sitesearch=" target="_blank">Digital
telephony</a> </p>
<p>• <a href="http://www.google.com/custom?hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BLH%3A50%3BLW%3A300%3BGL%3A1%3BBGC%3AFFFFFF%3BT%3A%23000000%3BLC%3A%23000000%3BVLC%3A%23000000%3BALC%3A%23000000%3BGALT%3A%23000000%3BGFNT%3A%23999999%3BGIMP%3A%23999999%3BDIV%3A%23FF8400%3BLBGC%3AFF8400%3BAH%3Acenter%3BS%3Ahttp%3A%2F%2Fwww.audiocourses.com%3B&domains=audiocourses.com&q=digital%2Baudio%2BMicrowave%2Band%2Bradio%2Blinks&btnG=Search&sitesearch=" target="_blank">Microwave
and radio links</a> </p>
<p>• <a href="http://www.google.com/custom?hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BLH%3A50%3BLW%3A300%3BGL%3A1%3BBGC%3AFFFFFF%3BT%3A%23000000%3BLC%3A%230000CC%3BVLC%3A%230000CC%3BALC%3A%230000CC%3BGALT%3A%23008000%3BGFNT%3A%23000000%3BGIMP%3A%23000000%3BDIV%3A%230000CC%3BLBGC%3AFFFFFF%3B&q=digital%2Baudio%2BSatellite&btnG=Search" target="_blank">Satellite</a></p>
<ul>
<li><a href="http://www.google.com/custom?q=Audio%2BProduction%2BFor%2BThe%2BInternet&btnG=Search&hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1;L%3Ahttp%3A//www.audiocourses.com/images/logo2.gif;LH%3A50;LW%3A300;GL%3A1;BGC%3AFFFFFF;T%3A#000000;LC%3A#000000;VLC%3A#000000;ALC%3A#000000;GALT%3A#000000;GFNT%3A#999999;GIMP%3A#999999;DIV%3A#FF8400;LBGC%3AFF8400;AH%3Acenter;S%3Ahttp%3A//www.audiocourses.com;&domains=audiocourses.com" target="_blank">Audio
Production For The Internet</a></li>
</ul>
<p>General Links:</p>
<p><a href="http://www.google.com/custom?domains=audiocourses.com&q=Transmission%2Bof%2Bdigital%2Baudio%2Bin%2Bbroadcast%2Bproduction&sitesearch=audiocourses.com&sa=Search&client=pub-8263957883925270&forid=1&channel=6163154558&ie=ISO-8859-1&oe=ISO-8859-1&cof=GALT%3A%23000000%3BGL%3A1%3BDIV%3A%23FF8400%3BVLC%3A000000%3BAH%3Acenter%3BBGC%3AFFFFFF%3BLBGC%3AFF8400%3BALC%3A000000%3BLC%3A000000%3BT%3A000000%3BGFNT%3A999999%3BGIMP%3A999999%3BLH%3A50%3BLW%3A300%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BS%3Ahttp%3A%2F%2Fwww.audiocourses.com%3BFORID%3A1%3B&hl=en" target="_blank">Audiocourses.com
search</a></p>
<p><a href="http://www.google.com/custom?hl=en&lr=&ie=ISO-8859-1&oe=ISO-8859-1&c2coff=1&client=pub-8263957883925270&cof=FORID%3A1%3BL%3Ahttp%3A%2F%2Fwww.audiocourses.com%2Fimages%2Flogo2.gif%3BLH%3A50%3BLW%3A300%3BGL%3A1%3BBGC%3AFFFFFF%3BT%3A%23000000%3BLC%3A%23000000%3BVLC%3A%23000000%3BALC%3A%23000000%3BGALT%3A%23000000%3BGFNT%3A%23999999%3BGIMP%3A%23999999%3BDIV%3A%23FF8400%3BLBGC%3AFF8400%3BAH%3Acenter%3BS%3Ahttp%3A%2F%2Fwww.audiocourses.com%3B&domains=audiocourses.com&q=Transmission%2Bof%2Bdigital%2Baudio%2Bin%2Bbroadcast%2Bproduction&btnG=Search&sitesearch=" target="_blank">Google
Search</a></p>
<p> ;;</p>
<p>Questions:</p>
<p>1. Explain the basic difference between downloading text & graphics files
as compared to the streaming of a sound file over the internet.</p>
<p>2. Describe the process of creating a DVD master</p>
<p>3. Explain the authoring process in creating a DVD for full production film.</p>
<p>4. Describe,. with particular regard to the method of billing, the DIVX system.</p>
<p>5. Discus briefly the problems of Data Streaming on the Internet.</p>
<p>6. What is Eureka 147?</p>
<p>7. Describe the current state of DAB in the UK</p>
<p>8. What is SDARS?</p>
<p>9. Explain the term repeater.</p>
<p>10. Explain Lossy data compression.</p>
<p>11. What is meant by the The psychoacoustic model?</p>
<p>12. What is ASIASTAR?</p>
<p>13. Describe how IP Telephony works. (<a href="http://www.intel.com/network/csp/resources/white_papers/4070web.htm" target="_blank">link</a>)
_________________
It's all in the ears. - Learn the concepts not the software.
Audio Courses is a way into the music business for you
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Mon Oct 31, 2005 11:38 am |
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rachelh
Joined: 16 Jan 2005
Posts: 35
Location: Trinidad WI |
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1. Explain the basic difference between downloading text & graphics files
as compared to the streaming of a sound file over the Internet.
When a text or graphic file is downloaded off of the Internet it can be recorded [burnt] onto CD’s or DVD media, placed on a floppy disk and generally be distributed without encountering problems, that is, if there are no of licensing arrangements and technological barriers associated with the file. But in all instances what distinguishes a downloaded file from a streamed sound file [like those present in Internet Radio] is that streamed sound files can be listened to when the user is online but cannot be saved onto the hard drive. In instances where these files can be saved the bitrate of the audio is reduced so that the quality of the file makes it futile for the user to transfer to CD or distribute as degradation will un -doubt ably make the audio quality worse.
http://www.fingertipsmusic.com/downloading_versus_streaming.htm
2. Describe the process of creating a DVD master
Taken from:
http://www.mastermix.com/dvdhome
The process of creating a DVD-V master, or authoring, incorporates the following basic steps:
Project Planning
· Flowchart to describe how the various elements of the project work together, and bit-budget decisions.
Asset Acquisition
· Gathering of the assets or source materials to be used, i.e. edited video, stereo and/or multi-channel audio, and menu elements. Source material should be reviewed and documented in detail.
Encoding
· Source material must be encoded into DVD-compliant form. This is typically the most time-consuming part of any DVD project. Encoded materials are quality-checked in real-time.
Navigation
· A set of navigational instructions are necessary for the end-user to control viewing of the completed production.
Imaging
· The encoded assets, along with the navigational info, are multiplexed into a DVD-compliant stream. This 'stream' is played and checked for proper operation.
Ref Disc & QC
· A playable, high-quality authoring DVD-R is 'burned' with the disc image, and submitted to the client for approval.
Delivery Master
· Following client approval, a delivery master is generated. All delivery masters are evaluated for sonic and/or data errors.
All DVD-Video processes are performed and verified in-house, using Sonic Creator and Interactual Image Builder 2.0, and checked on a variety of platforms. More elaborate out-of-house verification can be provided if requested.
3. Explain the authoring process in creating a DVD for full production film.
The process of DVD authoring for full production film is as follows:
The hardware and tools for the process have to be aquired, for example:
· DVD+R &DVD+RW:
· DVD-R & DVD-RW:
· DVD-RAM: This format is not suitable for DVD-video
· DV camera
· A Firewire (IEEE1394) Card
· Loads of Disk Space
· A Fast CPU
· Software
Then, processing – the process of making sure that the basic movies are ready takes place. The Menu is then written, then the background, subtitles and the control file are then inserted…
“One of the big advantages of DVD over video is that it is a random-access medium which means that it is possible to have menus which allow you to select what you want to see, rather than having to scan to roughly where you want which is both time-consuming and inaccurate (at least on my VCR).
To understand menus (and in particular the limits of what can be done with dvdauthor) you need a basic understanding of the hierarchy of structure within a video DVD.
TitleSet
This is the highest level of structure within a video DVD. Every DVD has at least 1 titleset. All the files associated with a given titleset start with VTS_nn where nn is the titleset number (starting from 1).
Title
Each titleset contains 1 or more titles. Each title is effectively a standalone movie. If you start xine and just tell it to play a dvd, and that dvd doesn't have a top-level menu, then it will just play the first title of the first titleset and then stop.
Chapter
Titles are subdivided into chapters. Chapters provide entry points to the movie, but when the player reaches the end of a chapter it will continue to the next chapter.
Menus can be associated with either the whole disk (VMGM) or with a titleset (VTSM), there can be more than one menu of either type. The simplest use of menus is to navigate within the disk. There are some limitations on the targets of navigation menus:
· A VMGM menu can only jump to:
o Another VMGM menu
o The first VTSM of a titleset
o The start of a titleset
· A VTSM menu can only jump to
o Another VTSM in the same titleset.
o A title or chapter within the titleset.
o The first VMGM of the disk
· There are a number of other useful targets for menus (use dvdauthor --help for a list).
The basic process of creating a menu is described in the document menu.txt in the current version of dvdauthor, however there are a few extras to bear in mind.
1. The menu is actually implemented as an mpeg movie with subtitles.
2. It appears to be necessary to add a (possibly silent) sound file into the mpeg for it to work.
3. Button coordinates are measured from top-left (which is conveniently the same as the gimp's coordinate system), however if you use the recipe here, you do not need to give explicit button coordinates.”
Making the menu
Menus are just an mpeg file with subtitles. The basic mpeg is the background and the subtitles produce the menu buttons. The background can either be a short movie or a still image converted to an mpeg, in the example here we use the latter.
This example assumes reasonable familiarity with the gimp.
There are probably many other ways to do this, but this is a route with which I am comfortable.
The background.
This is just a short (even single-framed) mpeg-2 file. It appears to need a sound track even if it is just silence. If you are working from a scanned image or an image from a still camera, you need to be aware that DVDs have non-square pixels, this can be handled either with the DPI in gimp or the aspect settings in the mpec encoding process (generally I use the latter for no better reason than I figured the correct settings there first).
Create your background image this should also contain any text that is part of the buttons (in this case it's just a title on the gimp's waves pattern. For PAL this image should be 720x576 pixels, for NTSC it should be 720x480 (SECAM I don't know). It is recommended to save this image in JPEG format.
The sound track can be made by recording a short (couple of seconds) sample from a sound card with nothing connected, and then converting it to an mp2 format with mp2enc. This shold be done at 48kHz sampling rather than the more common (for CDs) 44.1kHz.
If you are going to use a short movie clip, the you don't have to make a background image, just use the clip as the argument of spumux after following the procedure described here to make the subtitle images.
The subtitles.
Create your subtitle images. There are in fact 3 of them: the basic subtitles image which is used to show buttons in their "quiet" state, the highlight image which shows when a button is under the cursor, and the selected image which shows after the button has been clicked until its action has begun. If you are going to use automatic button identification (and why not it's a lot easier) you need to have transparent space between the locations in all the images. It will also make life easier if you put your buttons in nice rows and columns (the menu generator can handle either row-major or column-major layouts). I suggest using the guide bars in gimp to make a nice grid. It is recommended to save these images in PNG format. I shall not attempt to give a gimp tutorial here, there are many on the web, most of them far better than I could manage.
There are a number of important points to note:
· There may be no more than 4 colours in any image.
· Therefore you should disable all antialiasing (text tool and selections).
· Saving in indexed mode with a colour table of size 3 helps to force this (transparent is a colour in subtitle menus but not in gimp colour tables). RGB mode images are accepted but they won't check that you haven't got too many colours.
In the example here, the basic image (main6.png) is just the button texts in black, the selected image (main6s.png) is the same thing but with red text, while the highlight image (main6h.png) adds a background to the buttons (and will thus be the one that defines the sizes). If you make use of the gimp's save as option and do the images in that order, you won't need to retype the text with the consequent worries about alignment. I like to have a systematic naming convention for the images as that allows a simple shell script to make the menu mpeg files.
The control file
spumux, the subtitler in current versions of dvdauthor uses an XML control file to define how the subtitles are created.”
http://www.tappin.me.uk/Linux/dvd.html
4. Describe, with particular regard to the method of billing, the DIVX system.
TAKEN FROM:
http://www.utexas.edu/coc/rtf/kyle/VCroes%20Project/index2.htm
DIVX is an in-home movie viewing system using a modified DVD player. A consumer who purchases a DIVX player but who would like to have the rental option, as opposed to buying DVD discs, will be able to rent Divx movie discs with digital quality. The purchase price of the movie disc includes a two-day viewing period, which begins only when the consumer inserts the disc into a Divx player and pushes the play button, regardless of when the disc was purchased. Discs can be paused, stopped and played multiple times during the viewing period. The consumer essentially owns the disc and is therefore never required to return it.
Some movie discs will also have the option to be converted, through the player, to unlimited viewing for a one-time fee. Certain titles will also be available for purchase in the store as unlimited viewing discs, called DivxGold discs, which are initially purchased in the store as unlimited play discs that may be played without charge on any Divx player.
For optimal sound performance, the Divx player supports multi-channel digital sound, including Dolby's AC-3 surround sound audio format. The Divx player also supports digital audio output for use with an external DAC (Digital-to-Analog Converter), and a multitude of other sound components. Divx players are equipped with S-video and, on higher-end players, Component video output to ensure high visual quality. Divx also offers the highest horizontal resolution (480 lines) and colour resolution of any mainstream consumer video format, with less video noise and a vibrant colour spectrum.
The Divx system allows consumers to purchase physical ownership of a special encrypted movie disc that is the same size as regular audio compact discs. Divx players will have the capability to play all standard DVD discs, as well as compact discs. However, Divx players are the only DVD players that can play Divx movie discs, with their rental convenience. Viewing periods for a "rented" disc will normally be two days. A movie must be rented again, through the player, for additional viewing periods.
The consumer owns the disc and is therefore never required to return it but you cannot watch it again after the two-day viewing period without purchasing it through the player again. For many titles, the consumer will be able, through the player, to convert a disc to unlimited viewing for a one-time fee. Certain titles also will be available for purchase in the store as unlimited viewing discs (Divx gold discs). The Divx player will connect to a television in the same manner as a standard DVD player although a VCR connection is not recommended because of the copy protection technology. It will also not connect to your cable box. The other difference will be that a phone line must be connected between a phone jack in the wall and a jack in the back of the unit. A standard phone jack is all that is required, and the phone line is not used while the movie is in progress.
Occasionally, the Divx-enhanced player periodically places a toll-free call to the Divx processing centre to send billing information but the phone line and host connection are only used during off-hours. The Divx player never has to call in before you watch a movie and no new phone line is required since the player never interferes with the consumer's phone usage. However, if the consumer tries to use the telephone during a Divx player transaction call, the Divx player will automatically disconnect the call and attempt the call at another time. The player does not have to make a connection to the host computer for the customer to view a movie so the player will continue to play Divx discs even if the modem line is not connected for a short time. The information required to authorize and decrypt discs is stored in secure memory in the player.
If a phone jack is not convenient to the player location, the consumer can install a new phone jack or purchase a wireless phone jack, which works through normal electrical outlets.
All movies available through the Divx system are fully encrypted utilizing triple DES (a term used to describe a long-used cryptographic standard) encryption. The discs and players are individually serialized, allowing the system to receive accounting information from players on a disc-by-disc or viewing period basis.
Consumers who purchase Divx players will establish an account with Divx for billing of any additional disc rentals beyond the initial two-day viewing period and any rental disc conversions to unlimited viewing. The player periodically calls the Divx processing centres toll-free number in the "off-hours" to send billing information.
Divx player will cost anywhere from $50 to $200 more than the standard DVD player. The rental price for a two-day viewing period will be $4.49, with additional viewing periods at about $3. Purchasing DivxGold discs or converting a disc to unlimited viewing will be comparable to the price of a standard DVD disc.
Divx players were formally introduced at the Consumer Electronics Show in January 1998 with national availability expected by early summer. Some manufactures such as: JVC, Matsushita/Panasonic, Thomson Consumer Electronics, and Zenith expect to distribute DVD players with the Divx capability through their standard retail outlets, including consumer electronics specialty stores and general merchandise retailers.
Disney, Paramount, Universal, DreamWorks SKG, and 20th Century Fox have agreed to make available on Divx discs all new releases at the same time as their Home Video VHS products. Some catalogue titles will also be available from Disney, Paramount, Universal, and Fox.
ADDITIONAL INFORMATION: PRO’S AND CONS:
What's Good
1. Divx-equipped players will play all standard DVD discs and audio compact discs.
2. You don't have to 'rent' the disc right before the rental.
3. You will not have to return the disc, eliminating potential for late fees.
4. To rent the same movie a 2nd time you don't have to get to the video store again.
5. There are parental controls on the player to limit number of rentals and purchases as well as which movie ratings can be watched.
6. The information that Divx will receive about a specific consumer's viewing habits will be used for internal control purposes only and will not be provided to third parties.
7. The Divx discs can be recycled, and Divx expects to create a recycling plan.
What's Bad
1. The account for other Divx players will be charged the rate for a first-time rental if someone else's disc is played on their machine, even if it has been converted to unlimited play.
2. Divx rental discs cannot be played on standard players.
3. The rental fee will be higher than that of ordinary DVDs.
4. The plastic disc will be thrown away if the consumer does not want to keep the disc, since it does not have to be returned. This is certainly an environmental concern. Although a recycling plan is being created, Divx will not have one in place until waste (the discs) are at meaningful levels
5. All DVD players purchased by consumers will be obsolete if Divx becomes accepted; only a couple of years after DVD was launched.
6. There is some potential for confusion of the Divx system with regular DVD's.
7. Paying full price to get an unlimited rental period will not be possible with all titles.
8. If a movie is put into the player by accident or you choose the wrong movie, you would be billed for that viewing regardless.
9. If the Divx system catches on, they are considering offering some Divx movies at the same time a movie hits theatres. This could be an end to the local cinema.
10. If you move to a location where Divx systems are not available, your entire Divx movie collection becomes worthless.
11. If the Divx project ever "shuts down" or ends for any reason, your player and discs become useless.
Also see http://www.robertsdvd.com/divx.html for more DIVX pros and cons.
5. Discus briefly the problems of Data Streaming on the Internet.
The problems associated with data streaming over the Internet are as follows:
1. Long transfer times
2. Playback latency
3. streaming audio programs are considerably further along than video, they are still nowhere near typical computer-sound quality
4. Streaming media companies aim to make Web video as seamless as television, but recent advances in technology may fall short of solving deeper problems with data delivery over the Internet.
5. Quality and cost issues in Internet streaming
6. Technology innovations in media players address a major piece of the puzzle in delivery of rich data such as video over IP (Internet Protocol), a method for sending data from one computer to another on the Internet. But the potential for delays and data jams on the Internet still exists.
7. In fact, one of the Web's greatest strengths can be thought of as its weakness when it comes to streaming media. The architecture of the Internet is designed to offer a set of redundant pathways for ferrying "packets" of content -- if one byway is jammed, chunks of data can be zapped through another. Though it's a nearly flawless system for sending text, audio and video can suffer hiccups in the stream when they are broken up and rerouted.
8. Packet loss and delays
http://insight.zdnet.co.uk/hardware/servers/0,39020445,2109779,00.htm
http://archive.dstc.edu.au/RDU/staff/jane-hunter/video-streaming.html
6. What is Eureka 147?
Background… taken from: http://www.worlddab.org/eureka.aspx#Why%20Eureka%20147?
A Technical body exists under the name of Eureka, which represents many technical projects that have been pursued throughout the years. Under the vast umbrella of the technical body of Eureka, the project that initiated the Digital Audio Broadcasting System, turned out to be the 147th technical project. Thus, the DAB project was adequately named Eureka 147 and to subsidise the project a consortium of members was created. Hence the name The Eureka 147 Consortium.
This project developed a new digital transmission system which received ITU recognition as a world standard - the only one to meet its stringent requirements. The Eureka 147 DAB System is now seen as the future of radio.
Taken from: http://web.archive.org/web/20040401020811/http%3A//www.bbc.co.uk/rd/pubs/papers/paper_21/paper_21.html
The Eureka 147 Digital Audio Broadcasting system is the most significant advance in radio technology since the introduction of FM stereo. It offers both listeners and broadcasters a unique combination of benefits and opportunities. These are:
· High-quality digital audio.
· Rugged, reliable delivery to fixed, portable and mobile receivers for interference free reception.
· Efficient use of the limited radio frequency spectrum available
· Flexibility and choice -- The DAB signal is essentially a highly flexible over-air 'data-pipe' that can broadcast a wide range of service types, from purely audio-based to multimedia. Typically, each multiplex can broadcast five or more high-quality audio services plus a number of extra services. The multiplex can be dynamically reconfigured to introduce additional services, temporary or permanent, either with time-of-day or on a day-to-day basis.
· System features that will allow 'easy-to-use' receivers to be developed.
· Added-value system features that will allow enhancements to existing radio services such as text, graphics and still-pictures, and provide the opportunity to introduce innovative new services, such as multimedia radio-with-pictures and broadcast web-sites.
Eureka 147 DAB is a reliable, multi-service, digital radio broadcasting system, designed specifically for robust reception by mobile, portable, and fixed receivers, using simple non-directional antennas. ETSI specification, EN 300 401 (Second Edition) specifies the transmitted DAB signal.
The Eureka 147 System comprises three main elements. These are:
· MUSICAM Audio Coding
· Transmission Coding & Multiplexing
· COFDM Modulation
Data for individual services, be they audio-based or data / multimedia, must be combined into a single data stream ready for transmission. This process is known as multiplexing, and the resulting data stream is called the multiplex.
The frame-based DAB multiplex (shown in Fig. 2) comprises three distinct elements:
· The Synchronisation Channel which conveys reference frequency and timing information to allow receivers to synchronise to and decode the received DAB signals.
· The Fast Information Channel (FIC), which carries information describing the composition of the multiplex and informs receivers how to extract and decode the information for individual services.
· The Main Service Channel (MSC) contains the audio frames or data packets corresponding to the different services within the multiplex. This part of the multiplex is essentially the useful payload of the DAB signal.
Reference:
http://en.wikipedia.org/wiki/Eureka_147
http://web.archive.org/web/20040401020811/http%3A//www.bbc.co.uk/rd/pubs/papers/paper_21/paper_21.html
http://www.worlddab.org/eureka.aspx#Why%20Eureka%20147?
7. Describe the current state of DAB in the UK
“The Digital Audio Broadcasting (DAB) System developed within the Eureka 147 Project and now standardised by the European Telecommunications Standards Institute provides the means to deliver high-quality digital radio services to the listener. In the United Kingdom, the BBC is pioneering the introduction of digital radio services by establishing a national transmission network for DAB, and exploring the potential of DAB to deliver exciting new programming that would have previously been impossible using existing analogue AM/FM radio systems.”
“In the United Kingdom, 12.5 MHz of Band III spectrum from 217.5 - 230 MHz has been allocated to DAB. This will accommodate seven multiplexes. The BBC has been allocated one of these channels for its national DAB multiplex to operate on a single frequency network of transmitters throughout the UK. The remaining six multiplexes are to be regulated by the Radio Authority and will be licensed to commercial broadcasters for national, regional and local independent radio services, starting in the Spring of 1998. The BBC's local & regional services will also accommodated within these multiplexes.
The BBC is committed to the introduction of digital radio in the UK and is establishing a single frequency network of 27 transmitting stations, that is on target for completion by Spring 1998. This SFN will initially serve at least 60% of the UK population and providing coverage to the major motorway routes.”
http://web.archive.org/web/20040401020811/http%3A//www.bbc.co.uk/rd/pubs/papers/paper_21/paper_21.html
8. What is SDARS?
Satellite Digital Audio Radio Service (SDARS) is:
1. A satellite-based direct-broadcast radio service in which digitally encoded audio entertainment material is broadcast to Earth-based receivers, either directly from an orbiting satellite, or--in cases in which the receiver is in a shielded location--from the satellite to the receiver via a repeater station.
2. A radiocommunication service in which audio programming is digitally transmitted by one or more space stations directly to fixed, mobile, and/or portable stations, and which may involve complementary repeating terrestrial transmitters, telemetry, tracking and control facilities.
3. A radiocommunication service in which compact-disc quality programming is digitally transmitted by one or more space stations.
Taken from: http://www.atis.org/tg2k/_satellite_digital_audio_radio_service.html
“SDARS will operate like a radio version of DBS (such as Direct TV or Primestar). The service provides audio-only broadcasting to small receivers using S-Band (2310 - 2360 MHz) frequencies. Normal AM/FM radios will not be able to receive this signal - new receivers must be purchased by consumers. The proposed systems will allow nationwide reception of 25-30 high definition music and voice channels in a wide variety of music and talk formats. Three of the four proposed systems will operate as commercial free subscription services, whereas one service - Primosphere proposes a free, advertiser supported service.”
http://www.lta.com/res_regulatory/sdars.htm
9. Explain the term repeater.
A repeater is:
1. An analogue device that amplifies an input signal regardless of its nature, i.e., analogue or digital.
2. A digital device that amplifies, reshapes, retimes, or performs a combination of any of these functions on a digital input signal for retransmission. Note: The term "repeater" originated with telegraphy and referred to an electromechanical device used to regenerate telegraph signals. Use of the term has continued in telephony and data communications.
3. A fixed transmitter that retransmits the signals of other stations.
Taken from: http://www.atis.org/tg2k/_repeater.html
10. Explain Lossy data compression.
A lossless or noiseless coding system is able to reconstruct perfectly the samples of the original signal from the coded (compressed) representation. In contrast, a coding scheme incapable of perfect reconstruction from the coded representation is denoted lossy. For most audio program material, lossy schemes offer the advantage of lower bit rates (e.g., less than 1 bit per sample) relative to lossless schemes (e.g., 10 bits per sample). Although the enormous capacity of new storage media such as digital versatile disc (DVD) can accommodate lossless audio coding the research interest and hence all of the algorithms we describe are lossy compression schemes that seek to exploit the psychoacoustic principles. Naturally, there is a debate over the quality limitations associated with lossy compression. In fact, some experts believe that uncompressed digital CD-quality audio (44.1 kHz/16 bit) is intrinsically inferior to the analog original. They contend that sample rates above 55 kHz and word lengths greater than 20 bits are necessary to achieve transparency in the absence of any compression.
PAINTER AND SPANIAS: PERCEPTUAL CODING OF DIGITAL AUDIO: http://www.eas.asu.edu/~spanias/papers/paper-audio-tedspanias-00.pdf
There are two basic lossy compression schemes:
· In lossy transform codecs, samples of picture or sound are taken, chopped into small segments, transformed into a new basis space, and quantized. The resulting quantized values are then entropy coded.
· In lossy predictive codecs, previous and/or subsequent decoded data is used to predict the current sound sample or image frame. The error between the predicted data and the real data, together with any extra information needed to reproduce the prediction, is then quantized and coded.
In some systems the two techniques are combined, with transform codecs being used to compress the error signals generated by the predictive stage.
http://en.wikipedia.org/wiki/Lossy_data_compression
11. What is meant by the The psychoacoustic model?
The Psychoacoustics of hearing refers to why and how the brain interprets a particular stimulus in a certain way. The psychoacoustic model graphically shows this and deals primarily with frequency masking… see http://www.cs.sfu.ca/CourseCentral/365/li/material/notes/Chap4/Chap4.4/Chap4.4.html
Masking refers to the phenomenon by which soft signals are ‘covered up’ due to the presence of loud signals, which are occurring at the same time. The greatest masking occurs when the frequency of the sound and the frequency of the masking noise are close to each other. Masking can be also be caused by harmonics of the masking tone. Equalisation might be required to make the instruments sound different enough to overcome any masking effects. –
Modern Recording Techniques – DM Huber, R Runstein
“Research shows that masking occurs with tones inside of frequency bands; a given tone will mask another tone within that band, but will not affect tones outside of that band; these are known as critical bands. The bandwidth of these bands increases as frequency increases, but can be approximated to be about 1/3 octave for frequencies between 300-20,000 Hz. The bands are not fixed, but are continuously variable and any audible tone will create a band centred on it. The masking tone raises the threshold of perceived hearing around that tone. Sound beneath that threshold is masked; however, sound outside of the tone's critical band will not be affected.” –
The Art Of Digital Audio – John Watkinson
The psychoacoustic model provides for high quality lossy signal compression by describing which parts of a given digital audio signal can be removed (or aggressively compressed) safely -- that is, without significant losses in the quality of the sound. It explains, for example, how a sharp clap of the hands might seem painfully loud in a quiet library, but hardly noticeable after a car backfires on a busy, urban street. It might seem as if this would provide little benefit to the overall compression ratio, but psychoacoustic analysis routinely leads to compressed music files that are 10 to 12 times smaller than high quality original masters with very little discernible loss in quality. Such compression is a feature of nearly all modern audio compression formats. Some of these formats include MP3, Ogg Vorbis, Musicam (used for digital audio broadcasting in several countries), and the compression used in MiniDisc.
Psychoacoustics is based heavily on human anatomy, especially the ear's limitations in perceiving sound as outlined previously. To summarize, these limitations are:
· High frequency limit
· Absolute threshold of hearing
· Absolute threshold of pain
· Temporal masking
· Simultaneous masking
Given that the ear will not be at peak perceptive capacity when dealing with these limitations, a compression algorithm can assign a lower priority to sounds outside the range of human hearing. By carefully shifting bits away from the unimportant components and toward the important ones, the algorithm ensures that the sounds a listener can hear most clearly are of the highest quality.
http://en.wikipedia.org/wiki/Psychoacoustics
12. What is ASIASTAR?
BACKGROUND:
WorldSpace is the world's first digital satellite radio network. It covers parts of Asia and Europe plus all of Africa by satellite. There are currently two satellites in use, AfriStar and AsiaStar.
AfriStar serves Africa, Europe, and the Middle East, while AsiaStar serves most of South Asia and overlaps in the Mideast. Plans to launch a third satellite, Ameristar, to serve South America were not carried out as the frequencies used by WorldSpace (L band) are commandeered by the United States Air Force.
Each satellite provides three transmission beams that can support 50 channels each, carrying news, music, entertainment, and education, and including a computer multimedia service.
http://en.wikipedia.org/wiki/AsiaStar
13. Describe how IP Telephony works.
IP [Internet Protocol] Telephony is the process by which persons can communicate in a real time environment via the use of IP telephony and the Internet, whereby the user speaks into a microphone attached to the computer and hears through the computer speakers. Since its inception in 1995, IP telephony has evolved and communication quality between users has increased. “Dozens of companies have introduced products to commercialise the technology, and virtually every major telecommunications company has launched research to better understand this latest threat to its markets.” [1]
In March of 1996, VocalTec announced it was working with an Intel Company (Dialogic Corporation, an Intel acquisition made in 1999) to produce the first IP telephony gateway. The original Internet telephone products based on multimedia PCs are tremendous - offering the ability to combine voice and data on one network. They also offer low-cost long distance "telephone" service (assuming the user already has a multimedia PC and a fixed-rate Internet service provider [ISP] account).
IP Telephony works via the use of Internet telephone gateways.
These gateways work:
“On one side, the gateway connects to the telephone world. It can communicate with any phone in the world. A phone line plugs into the gateway on this end. “ [1]
“On the other side, the gateway connects to the Internet world. It can communicate with any computer in the world. A computer network plugs into the gateway on this end. “ [1]
“The gateway takes the standard telephone signal, digitizes it (if it is not already digital), significantly compresses it, packetizes it for the Internet using Internet Protocol (IP), and routes it to a destination over the Internet.” [1]
“The gateway reverses the operation for packets coming in from the network and going out the phone.” [1]
“Both operations (coming from and going to the phone network) take place at the same time, allowing a full-duplex (two-way) conversation.” [1]
“A number of configurations can be built from this basic operation as described above:
1. Phone-to-PC or PC-to-phone operations can take place with one gateway.
2. Phone-to-phone PC operation can occur with two gateways. To offer international long distance service using gateways, for example, an organization or service provider can host one gateway in each country. By bypassing the international connect charges - even paying in-country long distance rates - the configuration costs significantly less than traditional circuit-switched service.” [1]
http://www.intel.com/network/csp/resources/white_papers/4070web.htm |
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Sat Nov 05, 2005 7:18 am |
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Polarman
Joined: 24 Jun 2005
Posts: 55
Location: Barbados |
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1. Explain the basic difference between downloading text & graphics files as compared to the streaming of a sound file over the internet.
The location of the song file that is being listened too is the main difference between downloading and streaming a song. When downloading, a song file is saved to a computer. The file can be retrieved at a later stage. Usually the download must be complete in order to play the media/open the file. One of the advantages of downloading is that once the file is downloaded it has been transferred from the Internet to a computer hard drive and it can then be treated as a file. The file can be stored for long periods of time, copied to different locations, distributed to others and it can be burned onto CD or DVD. However, not all downloads can be burned due to licensing and technological barriers. This type of downloads sometimes come with a built-in limitation on the number of times or period of time it can be used/listened to.
Streaming, on the other hand, means that the media plays while it is being transferred. When streaming, a song comes from another location on the Internet via a music stream. Once a song stream is stopped it cannot be retrieved from the computer’s hard drive. This is because streaming songs can only be listened to through a computer while it is online and they cannot be burned onto a CD. One of the benefits with streaming is that after only a few seconds of transferring the contents of the file can be determined. This instead of waiting through a lengthy downloading process and then discover that the content is not right. While streaming, if the download is slow the download fails or “times out”.
(Sing Fish – The Audio/Video Search Engine, 2005; Fingertips Music, 2005).
2. Describe the process of creating a DVD master
There are three steps needed to make a DVD complete: Authoring, Mastering and Replication and these tend to overlap. Both Authoring and Mastering involve encoding, and both Mastering and Replication involve a mastering process.
When the DVD is mastered after authoring the DVD is compiled into its fully encoded components (called multiplexing). When replicating the full DVD, a second master is produced. That process is just like making printing plates for the press. When replicating DVD's and CD's the master is used to make a glass master. This is then used in the replication machines.
To keep the project under control it’s good to set up a flowchart with the various elements involved. The first step is to gather all or source materials that should be on the DVD that can be video, stereo and/or multichannel audio, and menu elements. The material must be encoded into DVD-compliant form and reviewed and documented in detail. This is typically the most time-consuming part of any DVD project. The encoded materials with the navigational info are then multiplexed into a DVD-compliant stream. This stream is played and checked for proper operation. After this DVD-R is "burned" after approval the DVD Video/Audio master is generated (Mastermix, 2005; Xolara, 2005).
3. Explain the authoring process in creating a DVD for full production film.
Authoring is the process of asset acquisition, menu design, DVD navigation construction, collecting audio, video, menus, subtitles, interviews, alternative endings/scenes etc into an interactive branching structure that will eventually become a playable DVD. In the authoring process for full production film it is important to check the data bandwidth since the visual material can vary between slow simple scenes to complex scenes that use a lot of bandwidth. Its important that the maximum data rate is not exceeded. Once this is checked next step is data compression. The step after this is the creation of the master (Xolara, 2005; Audio Intervisual Design, 2005).
4. Describe, with particular regard to the method of billing, the DIVX system.
To be able to use DIVX, which is an in-home movie viewing system, you need a modified DVD player. A consumer who purchases a DIVX player will be able to rent Divx movie discx with digital quality. The DIVX player can also be used to play normal DVDs, the rental service is only an option. The purchase price of the movie disc includes a two-day viewing period, which begins when the consumer inserts the disc into a Divx player and pushes the play button. It doesn’t matter when the disc was purchased the start period is triggered as mentioned above. Discs can be paused, stopped and played multiple times during the viewing period. The consumer essentially owns the disc and is therefore never required to return it.
Consumers who purchase Divx players will establish an account with Divx for billing of any additional disc rentals beyond the initial two-day viewing period and any rental disc conversions to unlimited viewing. The Divx-enhanced player places a toll-free call at regular intervals to the Divx processing centre to send billing information but the phone line and host connection are only used during off-hours. There is never a need for the Divx player to call in before the costumer watches a movie, and no new phone line is required since the player never interferes with the consumer's phone usage. But, if the costumer tries to use the telephone during a Divx player transaction call, the player automatically disconnects the call and tries the call at another time. The Divx player does not have to make a connection to the host computer for the customer to view a movie so the player will continue to play Divx discs even if the modem line is not connected for a short time.
The rental price for a two day viewing period will be $4.49, with additional viewing periods at about $3. Purchasing DivxGold discs or converting a disc to unlimited viewing will be comprable to the price of a standard DVD disc. The prices mentioned are valid when the referred article was written (Digital Video Express, 2005).
5. Discus briefly the problems of Data Streaming on the Internet.
A file can be streamed when the file has been greatly reduced. Streaming makes it possible to receive the file as fast as it can be played. It is somewhat difficult to stream audio files because the file size must be small and it must also cope with the packet-switching transmission method of the Internet. Packets usually arrive in sequences and some packets may be missing, having to be retransmitted. This retransmission incurs a delay. To avoid interruptions in the flow of data causing interruptions in the playback signal a buffer is needed. Another challenge to streaming audio is that data speeds across an Internet path differs according to traffic conditions and the path itself. The challenges of streaming audio are increased when accompanied by streaming video (Pohlmann, 2005).
6. What is Eureka 147?
Eureka 147, more commonly know as Digital Audio Broadcast (DAB), is a protocol for digital radio broadcasting. It was originally developed in Europe, but is now being deployed in many countries around the world. Eureka 147 was selected as the European standard in 1995 for broadcasting to mobile, portable and fixed receivers. A Technical body exists under the name of Eureka, representing many technical projects that have been pursued throughout the years. Under the technical body of Eureka, the project that initiated the DAB System, turned out to be the 147th technical project. Consequently, the DAB project was named Eureka 147 and to subsidise the project a consortium of members was created (Eureka 147 Consortium). The project developed a new digital transmission system which received ITU recognition as a world standard - the only one to meet its rigorous requirements. The Eureka 147 DAB System is now seen as the future of radio.
Eureka 147 is most often transmitted in the L band, from 1452 to 1492 MHz, but can also operate in VHF and UHF bands in some countries. Several radio stations share a single radio signal by multiplexing their digital audio bitstreams together, being later decoded at the receiver (Pohlmann, 2005; Wikipedia – The Free Encyclopedia, 2005; World DAB, 2005).
7. Describe the current state of DAB in the UK
Digital radio has struggled to compete with analogue radio which has a strong postion, particularly in Europe. Analogue radio is well established in people’s homes, receivers are cheap and broadcasters have tried and tested, working business models. But over the last two (since 2002) years in the UK, a new way of doing business has been adopted and consumers have been flocking to adopt digital radio.
In 2004 there were local multiplexes all over the country, with over 50 stations available in London, 30 in Birmingham and 27 in Liverpool. The multiplexes were awarded to operators through a bidding system which took into account the ability of the bidders to fund and run the transmitters. The multiplex operators then offered slots to radio stations on a purely commercial basis, depending on how much bit rate the stations used. This encouraged new smaller stations with lower bit rates to go “digital only” from the start.
Another major driver for the development of stations on DAB was the terms of the licenses that are issued by the UK government. This encourages existing analogue stations to move to digital by automatically extending their analogue licenses for up to 12 years if they launched a digital station. This was a real advantage as the license renewal was not automatic and re-applying is costly and risky. This encouraged the transition to digital among broadcasters, and provided a breathing space for large radio groups to invest in digital radio without pressure from investors.
The development of the market was a challenge that took co-operation and a different approach to the market. A change came in 2002 with the sponsored development of a portable kitchen radio at a consumer price point. The consumer was set in focus. This lead to the creation of the new stations, and the DRDB, which is funded by both the BBC and the commercial radio broadcasters in the UK specifically to promote digital radio, often using traditional analogue radio to advertise the new digital-only stations (Radio Scape, 2004).
8. What is SDARS?
Satellite Digital Audio Radio Service (SDARS) is the US Federal Communications Commission´s (FCC) term for satellite radio, currently being made popular in the U.S. by XM Radio and Sirius. SDARS operates like a radio version of DBS. The service provides audio-only broadcasting to small receivers using 2.3-GHz S-Band, from 2320 to 2345 MHz frequencies. Normal AM/FM radios will not be able to receive this signal. Terrestrial repeaters retransmit the signals in areas that are prone to weak signals, due to obstructions like tall buildings in downtown areas (Wikipedia – The Free Encyclopedia, 2005; Leslie Taylor Associates, 2002).
9. Explain the term repeater.
A repeater is a device or a combination of devices that amplifies or sometimes even cleans the signal and retransmits it. This makes it possible to send the signal longer distances or a possibility to redistribute to different locations. A repeater works and looks different in different communications systems. Here are some examples of how repeaters work within different communication system:
a) In digital communication systems, a repeater is a device that receives a digital signal on an electromagnetic or optical transmission medium and regenerates the signal along the next leg of the medium. A series of repeaters make possible the extension of a signal over a distance. Repeaters remove the unwanted noise in an incoming signal. Even if the signal is weak or distorted it can be clearly perceived and restored. Digital signals tend to dissipate more quickly than analog signals and need more frequent repeating.
b) In a wireless communications system, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas. The transmitter produces a signal on a frequency that differs from the received signal. This so-called frequency offset is necessary to prevent the strong transmitted signal from disabling the receiver. The isolator provides additional protection in this respect. A repeater, when strategically located on top of a high building or a mountain, can greatly enhance the performance of a wireless network by allowing communications over distances much greater than would be possible without it.
c) In satellite wireless, a repeater (more frequently called a transponder) receives uplink signals and retransmits them, often on different frequencies, to destination locations.
d) Repeaters are commonly used by commercial and amateur radio operators to extend signals in the radio frequency range from one receiver to another. These consist of drop repeaters, similar to the cells in cellular radio, and hub repeaters, which receive and retransmit signals from and to a number of directions (Search Networking.com, 2005).
10. Explain Lossy data compression.
Lossy data compression method is when data is compressed and then decompressed retrieving data that may well be different from the original, but is similar enough to be useful in some way. This type of compression is often used on the Internet, especially in streaming media and telephony applications. These methods are referred to as codecs in this context. Lossy data compression often suffers from generation loss (compressing and decompressing multiple times will do more damage to the data than doing it once). This generation loss depends on the design of the data format (Wikipedia – The Free Encyclopedia, 2005).
11. What is meant by the psychoacoustic model?
Psychoacoustics is the study of subjective human perception of sounds, the study of psychology of acoustical perception. It is heavily based on human anatomy, mainly the ear’s limitations in perceiving sound (Wikipedia – The Free Encyclopedia, 2005). Psychoacoustic models imitate the human hearing system and analyse spectral data in order to determine how the audio signal can be coded to render quantisation noise as impossible to hear as possible.
High quality lossy signal compression is provided through the psychoacoustic model. This is done by describing which parts of a given digital audio signal that can be removed safely, without significant losses in the quality of the sound. The model determines how much coding noise is allowed in every critical band, performing one such analysis on each frame of data. Psychoacoustic analysis normally leads to compressed music files that are 10-12 times smaller than high quality original masters with very little noticeable loss in quality. This compression is used in almost all modern audio compression formats such as the MiniDisc, MP3, Oqq Vorbis and Musicam (Pohlmann, 2005; Wikipedia – The Free Encyclopedia, 2005).
12. What is ASIASTAR?
The US-based organization, WorldSpace Corporation, is the world´s first digital satellite radio network. The company provides direct satellite delivery of digital audio and multi-media communications services to parts of Asia, Europe and all of Africa. WorldSpace is also licensed to serve Latin America and the Caribbean. The operational system broadcasts audio, text and images using a new generation of low-cost portable receivers. Major content partners are CNN, NPR, BBC, Fox News and Virgin Radio. Many channels are known for high quality programs with almost CD quality audio.
There are currently two satellites, AfriStar launched in 1998 serving Africa, Europe and the Middle East and AsiaStar launched in 2000 serving most of South Asia and overlapping in the Middle East. There are plans to launch a third satellite, AmeriStar to serve South America (Sky Rocket, 2005; Wikipedia – The Free Encyclopedia, 2005).
13. Describe how IP Telephony works.
IP Telephony (Voice over Internet Protocol) also called VoIP, Digital Phone and Internet Telephony is the routing of voice conversations over the Internet or any other IP based network. The voice data flows over a general-purpose packet-switched network instead of traditional circuit-switched transmission lines. In other words, audio is sent on the Internet between two or more computer users in real time.
The first IP telephony software product was introduced by VocalTec in early 1995. Today there are various Internet Phones which enables the multimedia PC user to speak into a microphone and listen via speakers. The technology has developed since then and is today a threat to telecommunications companies. With IP Telephony conversations are easily possible on the Internet and due to this many companies have introduced products to commercialise the technology.
Gateways are the key to bringing IP telephony into the mainstream. By bridging the traditional circuit-switched telephony world with the Internet, gateways offer the advantages of IP telephony to the standard telephone. Another important IP telephony problem that is overcome through Gateways is addressing. To address a remote user on a multimedia PC, the user's Internet Protocol (IP) address must be known. To address a remote user with a gateway product, one only needs to know the user's phone number (Intel Telecom Resources, 2005).
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SOURCES:
Audio Intervisual Design. (2005).
http://www.aidinc.com/features/dvdfaq.asp
Digital Video Express. (2005).
http://www.utexas.edu/coc/rtf/kyle/VCroes%20Project/index2.htm
Fingertips Music. (2005).
http://www.fingertipsmusic.com/downloading_versus_streaming.htm
Intel Telecom Resources. (2005). IP Telephony Basics.
http://www.intel.com/network/csp/resources/white_papers/4070web.htm
Leslie Taylor Associates. (2002).
http://www.lta.com/res_regulatory/sdars.htm
Mastermix. (2005).
http://www.mastermix.com/dvdhome
Pohlmann, K. C. (2005).
Principles of Digital Audio. 5th ed. McGraw-Hill: New York.
Radio Scape. (2004). DAB in the UK – Why it has been so successful. http://www.radioscape.com/downloads/DAB_in_UK_Case.pdf
Search Networking.com. (2005). http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212890,00.html
Sing Fish – The Audio/Video Search Engine. (2005). http://search.singingfish.com/sfw/help/streaming.html#diff
Sky Rocket. (2005).
http://www.skyrocket.de/space/doc_sdat/worldstar.htm
World DAB. (2005).
http://www.worlddab.org/eureka.aspx
Xolara. (2005).
http://www.xolara.com/?page=services&service=12 |
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