SIGNAL SOURCES FOR SIMULATION, TESTING, AND CALIBRATION - Design and Development of Medical Electronic Instrumentation - page 272

erent compression algorithms. The for-
mat tag entry in the fmt chunk indicates the type of compression used. A value of 1 indi-
cates linear pulse-code modulation (PCM), which is a straight, or uncompressed, encoding
of the samples, which is just the exact amplitude of each sample. The fmt chunk describes
the sample format (Table 6.4), and the data chunk contains the sample data (Table 6.5). All
numeric data

The .wav speci fi cation supports a number of di ff

fields are in the Intel format of low-high byte (usually referred to as little-
endian ). Eight-bit samples are stored as unsigned bytes, ranging from 0 to 255; 16-bit sam-
ples are stored as 2's-complement signed integers, ranging from -32768 to 32767.
If you are a Matlab user, you can avoid the hassle of

fi

file formatting by playing a data
stream directly from within the Matlab environment using the “sound” command. Matlab can
also write .wav

fi

file PCM-encoded signal into data
that can be manipulated by Matlab. Another possibility is to use a professional waveform

fi files from data variables or read the .wav fi

TABLE 6.4 Contents of the Format Chunk of a .wav File

Offset Length (bytes) Contents

12 4 fmt

16 4 0x00000010

which is the length of the fmt data (16 bytes)

20 2 0x0001

which is the data-encoding format tag: 1 PCM

22 2 channels

which defines the number of channels: 1, mono; 2, stereo

24 4 sample rate

in samples per second (e.g., 44,100)

28 4 bytes/second

sample rate block align

32 2 block align

channels bits/sample/8

34 2 bits/sample

8 or 16

TABLE 6.5 The Data Chunk of a .wav File Contains the Actual Sample Data

Offset Length (bytes) Contents

36 4 data

40 4 length of the data block

44 As needed for data sample data

For multichannel data, samples are interleaved
between channels:
sample 0 for channel 0
sample 0 for channel 1
sample 1 for channel 0
sample 1 for channel 1
.
.
.
where channel 0 is the left channel and channel 1
is the right channel; the sample data must end
on an even byte boundary.