Exporting 3 time and getting 3 different files

[jerryct]

Hello,

while i edited some music i had to test whether different programs (xld and audacity) generate the same raw data. But i always got different results. Thus I wanted to systematically analyze the error in my tool chain and first made a test with audacity 1.3.12 alone.

1.) New Projekt with settings for the track Mono, 44100Hz 16-bit PCM and project frequency 44100Hz
2.) Generate silence with only 4 samples
3.) export 3 times to uncompressed RAW (header-less) signed 16-bit pcm
4.) display the 3 files with hexdump on mac os x 10.6.5

every file is different:

hexdump silence.raw
0000000 02 00 ff ff 00 00 00 00
0000008

hexdump silence2.raw
0000000 00 00 00 00 01 00 fe ff
0000008

hexdump silence3.raw
0000000 01 00 00 00 00 00 00 00
0000008

Honestly i am completly confused. I had expected that every file should be the same, because i only click 3 times on export and nothing else.
Can someone help me, where i am missing something?

jerry

[billw58]

What you're seeing is the application of dither to the exported files.

The actual sample values are:

silence1.raw: 2 -1 0 0
silence2.raw: 0 0 1 -2
silence3.raw: 1 0 0 0

Try going to Audacity > Preferences, Quality section, then under "High Quality Conversion" set Dither to "None".

-- Bill

[jerryct]

Ah, thank you - that helped.

With your hint i also searched in the audacity wiki for dither and there it is explained in detail.

jerry