AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 9 - Consumer Media and Digital Systems |
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Here I am leaving a more open approach for your research. I wish you to take each topic and investigate and provide suitable description for each point. Imagine you are explaining to someone who does not understand the area.
Describe and explain consumer media:
• Compact disc
• DVD-Video, as related to digital audio
• DVD-Audio, SACD and similar media of current relevance
• Mastering
• Manufacturing
• Physical and optical operation of the player
• Organisation of data and metadata
Describe and explain digital systems:
• System configuration
• Interconnection and routing
• Synchronisation
• Clocking
• Sample rate conversion
• SMPTE/EBU timecode in digital audio systems
• MTC in digital audio systems
_________________
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 Nov 01, 2004 11:01 am |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
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Week 9 – Consumer Media and Digital Systems
Describe and explain consumer media:
• Compact disc
The compact disc is the standard for consumer digital audio. The audio on a CD is 16-bit and the sampling frequency is 44.1KHz. The maximum capacity of an audio CD is 80 minutes. Since the audio has not been compressed, it is linear and at the highest quality possible for the medium. Different types of CD players can give different results as to the sound heard. The quality of the players Digital to Analogue converter can have an effect on the noise heard while silent passages in songs are played. The CD player also comes with error correction so if a CD gets scratched, it may not necessarily mean it won’t work flawlessly. The data that is lost can be reconstructed using interleaving and if the damage isn’t too great, no digital distortion will be heard.
• DVD-Video, as related to digital audio
DVD video provides crystal clear picture and did for video what the CD did for audio. The video data on the DVD is compressed using the MPEG2 so a DVD disc can hold hours of video instead of minutes with no degradation in the quality. The way the video is compressed is the same as how digital audio would be compressed using perceptual coding. Visual information that is irrelevant to the eye is left out so save space on the disc just as redundant audio data that is being masked is left out when coding audio.
• DVD-Audio, SACD and similar media of current relevance
DVD-Audio discs offer high-resolution multichannel audio plus extra content such as images and videos. They are playable in all DVD players and hybrid CD players. DVD-Audio discs use PCM to code the audio at a sample rate of 96KHz (more than twice the sample rate of a normal CD) and 192KHz for stereo content all at 24 bits.
SACD (Super Audio Compact Disc) is a higher resolution audio format but does not include any extra material such as video or still images and cannot be played on DVD players. SACD uses Direct Stream Digital (DSD) to encode the audio. It is a one-bit DSD with a bitrate of 2.8224 Mb/s, which is more than 64 times the sampling rate of CD (44.1KHz).
• Mastering
The process of creating a DVD Master includes:
Audio And Video Preparation/Encoding:
The audio and video data is encoded using a MPEG2 compression method. This reduces the data rate and saves space on the disc without any loss in the quality of the media. Video is encoded using the MPEG2 Variable Bit Rate Video Encoder, which reduces the video data while obtaining the maximum quality by leaving out redundant visual information and giving more bits for complex scenes and less for simple scenes. The MPEG2 Variable Bit Rate Audio Encoder is used to encode multichannel audio (5.1 or 7.1).
Subtitling/Disc Definition:
All included language versions of the subtitles are formatted in the Disc Definition stage with the other basic information about the disc.
Multiplexing:
The multiplexer takes all the audio/video and subtitle data and combines it into one single digital data stream.
Disc Building:
The encoded and multiplexed data is used by disc building software to create a final disc image. Here, information such as file structuring, synchronization of time codes, disc branching details for interactivity and disc content specified at the Disc Definition stage are combined.
Simulation:
Before the disc is pressed in volumes for manufacturing, a computerised simulation of the disc playback is carried out to confirm the data on the disc is correct.
Channel Encoding:
After the simulation has verified that the data on the disc is correct and the disc image has been created, error correction data must be added to the data stream. This is called channel encoding and it writes the DVD formatted data stream to the Laser Beam Recorder, which is used to cut the glass master DVD.
• Manufacturing
The DVD glass master is used to manufacture the high number of replications. The equipment used for the manufacturing is very expensive and can make replications at a rate of one every couple of seconds. The DVD-Video is also given CSS encryption and regionalization.
• Physical and optical operation of the player
The physical operation of a CD player is to encase the CD and rotate it so the optical laser can read it. Since CD’s are not the same size, the lens in the pickup must move up and down to achieve focus for separate discs. The focusing mechanism has a magnetized pole piece surrounded by a focusing coil. Electrical current passes through this coil to achieve focus. To read data without significant error, the lens has to be moved very precisely. A tracking coil that is wound around the same pole piece as the focusing coil handles this movement. This means the lens can move approximately 0.15 inches either way from its point of rest. The biggest difference between the focusing coil and the tracking coil is the force applied to them, which is vertical and horizontal respectively.
• Organisation of data and metadata
Since the data stored on the Minidisc is non linear, it is accessed in the same way as data on a hard disk. Data is stored in segments so editing is made easier. If you have 10 tracks on the Minidisc and erase track 4, which was a 3 minute song and then decide to record a new song that is 4 minutes long, the first three minutes of the track will be stored where track 4 used to be and the rest will be placed at the next available empty segment, which is after track 10. When playing back the new track, the read buffer keeps the track seamless while the Minidisc accesses the first segment and then the second. The Minidisc has a table of contents (TOC) that includes vital information about each track (number and location of the track).
Describe and explain digital systems:
• System configuration
A digital audio system can have the appearance of a mixer with a lot of features packed into it. There are the input and outputs either on the top or back of the system and faders, knobs and transport buttons on the surface. Other connectivity is also found on the back such as digital I/O’s, MIDI, Time Code, ADAT, Interface connection etc. There is usually an LCD screen for easy visual navigation through menus and settings. Onboard effects and EQ’s are also worked using the LCD screens in conjunction with the knobs and faders.
• Interconnection and routing
Virtually all channels and effects can be routed to any other output or input. Even the most compact of digital mixers can contain extensive routing, which can be beneficial if the mixer is lacking output busses and such. Many channels can also be grouped to one stereo output and from there a group plugin can be applied. All these routing settings can be stored and recalled when needed and instantly. All this routing is done internally within the system.
• Synchronisation
A digital system can be synced up to another piece of digital equipment in order to ensure that the two will play together. Two digital systems each have an internal clock but in order to be synched together, one has to be set as the master and the other the slave. They can be connected for sync using a wordclock.
• Clocking
Using a master clock to synchronize digital equipment is preferred because the master clock system synchronises to each component individually. This eliminates timing delays or jitter if the clock was sent through the signal chain sequentially. Using a wordclock for handling clocking information instead of having it go through the AES/EBU, ADAT or S/PDIF makes it independent of the audio information and therefore more stable.
• Sample rate conversion
The sample rate is the number of ‘snapshots’ that are taken of the incoming analogue audio in one second. The standard for CD’s is a sample rate of 44.1KHz (44100 snapshots every second). When working in a digital system, it is preferred to use a higher sample rate (96KHz) as to obtain a more accurate representation of the analogue signal and then convert the sample rate down to 44.1KHz when burning to CD.
• SMPTE/EBU timecode in digital audio systems
This time code is the standard for synching audio equipment as well as video equipment. A sequencer can be synched up to a video player while scoring a film.
• MTC in digital audio systems
MIDI time code is not as effective in synching audio since it is intended for MIDI. It interpret SMPTE time code using MIDI messages. MTC doesn’t pass on positioning information as accurately as SMPTE.
Last edited by iNSTiNCT2765 on Sat Nov 13, 2004 6:20 am; edited 1 time in total |
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Sun Nov 07, 2004 8:51 am |
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AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Good Stuff |
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Great stuff instinct, well done!
Just these two headings were too brief:
Synchronisation
Sample rate conversion
Make sure you have these concepts sorted.
_________________
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 Nov 08, 2004 7:07 am |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
There you go!  |
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Sat Nov 13, 2004 6:21 am |
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