inconsistent wavwrite/wavread behavior

[Randy Yates]

[NOTE: The following was emailed to ***@octave.org]

Octave normalizes the integers associated with wave files to 32767,
while matlab normalizes them to 32768. This means that the domain
of the signal vector x in octave is not [-1,+1] but

[-1 - 32768/32767, +1],

while the domain in matlab is

[-1, +32767/32768].

The attached zip file contains two files

1. a specially-generated .wav file, ramp.wav, that has the sequence
-32768 to +32767 repeated once;

2. a matlab script wavwritetest.m

If you extract both of these into a directory, then execute the script
wavwritetest in octave, you get this:

octave:1> wavwritetest
Input file 'ramp.wav' is RIFF format:
Total length = 262180 bytes
Number of channels = 1
Sampling rate = 48000 Hz
Data length = 131072 samples
yoctave =

-32768
-32767
-32766
-32765
-32764
-32763
-32762
-32761
-32760
-32759

ymatlab =

-32769.0000305185
-32768.0000000000
-32766.9999694815
-32765.9999389630
-32764.9999084445
-32763.9998779260
-32762.9998474075
-32761.9998168889
-32760.9997863704
-32759.9997558519

wavwritetest

yoctave =

1.0e+004 *

-3.27670000000000
-3.27660000305176
-3.27650000610352
-3.27640000915527
-3.27630001220703
-3.27620001525879
-3.27610001831055
-3.27600002136230
-3.27590002441406
-3.27580002746582


ymatlab =

-32768
-32767
-32766
-32765
-32764
-32763
-32762
-32761
-32760
-32759

This illustrates the problem.

[Randy Yates]

Post by Randy Yates
2. a matlab script wavwritetest.m

[x,Fs,nbits]=wavread('ramp.wav');
format long;
yoctave = 32767*x(1:10)
ymatlab = 32768*x(1:10)

[Randy Yates]

Post by Randy Yates
Octave normalizes the integers associated with wave files to 32767,
while matlab normalizes them to 32768. This means that the domain
of the signal vector x in octave is not [-1,+1] but
[-1 - 32768/32767, +1],

Sorry, that should be [-32768/32767, +1].