600 Chapter 20
that imitate their outboard hardware in a digital signal processor (DSP) program. This
software interfaces with mixing and editing programs (via mutually agreed data-exchange
standards) so as to provide the metaphor of “ outboard ” facilities on the desktop. These
programs are known as plug-ins.
20.2 Audio Data Files ...................................................................................................
Digital representations of sound, when stored on computer, are stored just like any other
kind of data, as fi les. A number of different fi le formats exist in common usage. Most
sound fi les begin with a header consisting of information describing the format of that
fi le. Characteristics such as word length, number of channels, and sampling frequency are
specifi ed so that audio applications can read the fi le properly. One very common type of
fi le format is the WAV (or Wave) format. This is a good example because it demonstrates
all the typical features of a typical audio fi le.
20.2.1 WAV Files
W A V fi les are a version of the generic RIFF fi le format. This was codeveloped by
Microsoft and IBM. RIFF represents information in predefi ned blocks, preceded by a
header that identifi es exactly what the data are. This format is very similar to the audio
interchange fi le format (AIFF) format developed by Apple (see later) in that it supports
monaural and multichannel samples and a variety of sample rates. Like AIFF, WAVE fi les
are big and require approximately 10 Mbytes per minute of 16-bit stereo samples with a
sampling rate of 44.1 kHz.Here is a hexadecimal representation of the fi rst 128 bytes of a
WAV fi le.
26B7:0100 52 49 46 46 28 3E 00 00–57 41 56 45 66 6D 74 20 RIFF( ..WAVEfmt
26B7:0110 10 00 00 00 01 00 01 00–22 56 00 00 22 56 00 00 ..... ” V.. “ V..
26B7:0120 01 00 08 00 64 61 74 61–04 3E 00 00 80 80 80 80 ...data. ..........
26B7:0130 80 80 80 80 80 80 80 80–80 80 80 80 80 80 80 80 ............
26B7:0140 80 80 80 80 80 80 80 80–80 80 80 80 80 80 80 80 ............
26B7:0150 80 80 80 80 80 80 80 80–80 80 80 80 80 80 80 80 ............
26B7:0160 80 80 80 80 80 80 80 80–80 80 80 80 80 80 80 80 ............
26B7:0170 80 80 80 80 80 80 80 80–80 80 80 80 80 80 80 80 ............