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3. Popular sampling rates.

Some sampling rates are more popular than others, for various reasons. Some recording hardware is restricted to (approximations of) some of these rates, some playback hardware has direct support for some. The popularity of divisors of common rates can be explained by the simplicity of clock frequency dividing circuits :-).

Samples/sec     Description

5500            One fourth of the Mac sampling rate (rarely seen).

7333            One third of the Mac sampling rate (rarely seen).

8000            Exactly 8000 samples/sec is a telephony standard that
                goes together with u-law (and also A-law) encoding.
                Some systems use an slightly different rate; in
                particular, the NeXT workstation uses 8012.8210513,
                apparently the rate used by Telco CODECs.

11 k            Either 11025, a quarter of the CD sampling rate,
                or half the Mac sampling rate (perhaps the most
                popular rate on the Mac).

16000           Used by the G.722 compression standard.

18.9 k          CD-ROM/XA standard.

22 k            Either 22050, half the CD sampling rate, or the Mac
                rate; the latter is precisely 22254.545454545454 but
                usually misquoted as 22000.  (Historical note:
                22254.5454... was the horizontal scan rate of the
                original 128k Mac.)

32000           Used in digital radio, NICAM (Nearly Instantaneous
                Compandable Audio Matrix [IBA/BREMA/BBC]) and other
                TV work, at least in the UK; also long play DAT and
                Japanese HDTV.

37.8 k          CD-ROM/XA standard for higher quality.

44056           This weird rate is used by professional audio
                equipment to fit an integral number of samples in a
                video frame.

44100           The CD sampling rate.  (DAT players recording
                digitally from CD also use this rate.)

48000           The DAT (Digital Audio Tape) sampling rate for
                domestic use.

While professional musicians disagree, most people don't have a problem if recorded sound is played at a slightly different rate, say, 1-2%. On the other hand, if recorded data is being fed into a playback device in real time (say, over a network), even the smallest difference in sampling rate can frustrate the buffering scheme used.

There may be an emerging tendency to standardize on only a few sampling rates and encoding styles, even if the file formats may differ. The suggested rates and styles are:

    rate (samp/sec) style           mono/stereo

    8000  8-bit     u-law  mono
    22050 8-bit     linear unsigned mono and stereo
    44100 16-bit    linear signed   mono and stereo

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