AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 2 |
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Straight into the questions, nice and simple to begin with.
As there are two of you on this module. t might be a great idea to get together and share notes and resources, chat over the topics maybe.
To that end, I'd like you to post your responses here and create some dialogue around these themes.
I envisage us dipping in and out regularly during the weeks to converse.
1. Explain the following.
a) Sample rate
b) Bit Depth
Give an account of how these two work together to determine quality in digital audio. Please feel free to upload sounds to use as examples. You may link to them here.
_________________
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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Sun Mar 11, 2007 9:17 pm |
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Rbro
Joined: 07 Sep 2005
Posts: 12
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| Sample Rate |
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Sample Rate
A sample rate refers to the amount of times the recorded sound is digitaly measured (sampled) in a second. The more the sound is sampled the more accuraty the sound can be reproduced e.g. if you have 20 samples of a sound it can be more accuratley reproduced than if you only had 2 samples i.e There is more information avalible to reproduce the sound.
It is common place for audio CDs to be sampled at a rate of 44.1kHz (this rate was worked out in order for the original sounds to fit in with the video standards as samples were worked out on a video screen). The human ear has a range of 20Hz - 20kHz (approx) and samples should be twice the rate of the highest frequency therefore a sample rate of 44.1kHz covers all sounds audible by the human ear. The higher the frequency gets the less the sound gets sampled per cycle e.g. 100hz will have 441 samples of its waveform but 10KHz will have 4.41 samples of it's waveform. This is not noticible to most but some people say higher frequencies are repoduced poorly.
Bibliograpgy
http://www.pcguide.com/art/soundSampleRate-c.html
http://en.wikipedia.org/wiki/Sample_rate#Sampling_theorem |
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Mon Mar 12, 2007 8:03 pm |
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AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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OK good start Russell.
Now both you and Nancy, how about Bit Depth?
And then once that is defined:
"Give an account of how these two work together to determine quality in digital audio. Please feel free to upload sounds to use as examples. You may link to them here."
_________________
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 Mar 12, 2007 8:20 pm |
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Rbro
Joined: 07 Sep 2005
Posts: 12
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| Bit Depth |
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Bit Depth
While the sample rate defines how many times a sound is measured in a second the bit depth refers to the amount of data stored for every measure in the sample. At present the redbook standard is 16/44.1, 44.1kHz refering to the sample rate and 16 being the bit depth. Like sample rate, the higher the bit depth the more accurate the reproduction of the sound.
Bit is short for binary and is stored as a 1 or 0 (on or off). The more bits there are the more information that can be stored e.g 16 bits allows for 65,536 levels while 24 bits allows for 16,777,216 levels. These levels store all data about the recording e.g. dynamics, harmonics etc Just like pixles in a digital camera the more there are the clearer the image is. Obiously the higher the bit depth (and sample rate) the more storage space needed for the recording. Typically a 24 bit recording takes up 6 time the space as the same 16 bit piece.
As stated before, audio CD is recorded in 16/44.1, however 24/96 is now used in audio DVD and can be found in most professional digital recording equipment.
There is debate regarding 16/44.1 or 24/96, some say the quality should always be better however when put on a CD it shall be converted to 16/44.1 anyway so there's no point. There is also an interesting point that 24/88.2 is a better rate as 24/88.2kHz is an even number conversion to 44.1kHz.
I, personally, have always used 16/44.1 but after reading about higher sample rates and bit depth will definetly be experimenting.
Bibliography
http://www.tweakheadz.com/16_vs_24_bit_audio.htm
http://www.extremetech.com/article2/0,1697,1460722,00.asp
http://whatis.techtarget.com/definition/0,,sid9_gci213497,00.html |
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Mon Mar 12, 2007 9:15 pm |
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resol69
Joined: 31 Dec 2002
Posts: 69
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| from nancy |
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To convert analog sound to digital, the sound must be digitized using sampling. The sample rate means how often the signal is sampled, or the number of samples per second. The audio quality will improve as the number of samples per second increases. For lossless digitation, the sampling rate should be at least twice the maximum frequency response (called the Nyquist rate) The higher the sampling rate, the better.
A higher sample rate enables a more accurate reconstruction of a complex sound wave to be created from the digital audio file. To record high quality audio a sample rate of 44.1kHz should be used.
The bit depth refers to the number of bits you have to capture audio. The higher the bit depth, the better the sound, since there is a larger signal to noise ratio. The lower the bit depth, the more noisy the signal is. For example.
16-Bit has a signal-to-noise ratio of 98 dB -- virtually inaudible
8-bit has a signal-to-noise ratio of 50 dB, roughly twice as noisy as 16-bit.
The bit depth of the hardware or software you are using needs to match the bit depth of the sample for accurate playback.
Sample rate and bit size work together to create the quality of digitized audio. Examples:
Mono Telephone: 8Khz sample rate, 8 bits per sample
Mono AM Radio: 11.025 Khz sample rate, 8 bits per sample
Stereo FM Radio: 22.050 Khz sample rate, 16 bits per sample
Stereo CD: 44.1 khz sample rate, 16 bits per sample
When you put the bit depth and sample rate together, you can determine the bit rate. The bit rate is how how much data per second is needed to transmit the the file, or how big the file is. The bit rate determines how much storage space you will need for a digital audio file. The CD file mentioned above would take up 10.1 megabytes of file space per minute. |
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Sun Mar 18, 2007 2:58 am |
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AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Great |
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OK
Great work both did good here, we can move on from this now.
_________________
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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Sun Mar 25, 2007 3:33 pm |
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