Matters Concerning Audio - A Practical Guide to Video and Audio Compression - page 148

Vinyl or acetate disk

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78 RPM disk

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Open-reel tape (a.k.a. reel-to-reel or quarter-inch magnetic tape)

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Cassette tape

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CD

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SACD

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DVD

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Off-air analog radio or TV

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Off-air digital audio broadcasting (DAB)

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Downloaded audio files

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Sound stripe from the edge of the home movie film

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Optical sound track from 16mm or 35mm movie film

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Surround sound audio from a synchronized audio source

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Live recording

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Embedded audio

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Each of these recording mediums will introduce its own interesting features as well as
very specific shortcomings/advantages such as noise, bandwidth limits, and quality of signal.
Refer to Appendix M for descriptions of the many kinds of connector you will
encounter when connecting them together.

7.3.1 Analog Audio

Much of the legacy audio content is going to be delivered to you in the form of an analog
signal. Ingesting it converts it from an analog continuously variable waveform into a dis-
cretely sampled format.
You must determine suitable parameter values for the following:

The number of tracks to record in synchronization with one another

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The sample rate—bearing in mind the concepts based on Nyquist

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The bit value to indicate the resolution of the samples.

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All of these will materially affect the quality of the audio that you record. Figure 7-1
shows the end-to-end path for analog audio.

7.3.2 Digital Audio from a CD

If you are taking audio directly from a CD, it will be sampled at 44.1 KHz and deliver 2
channels (or tracks) at a sample size of 16 bits. It is likely to be presented in an AIFF or
WAV file container. The data rate of this content is about 150 Kbps . Figure 7-2 shows how
the analog waveform is sampled periodically.
Other audio formats are emerging but have not achieved significant market penetra-
tion. Look out for SACD and DVD audio disks and high-density DVD formats based on blue
laser technology. These may become dominant and will offer a greater capacity. This capac-
ity can be used to store more material or increase the bits available for each sample.