[ python-Bugs-1700821 ] audioop module - request to add a note

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Bugs item #1700821, was opened at 2007-04-14 18:07
Message generated for change (Comment added) made by rhettinger
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>Category: Documentation
Group: None
Status: Open
>Resolution: Accepted
Priority: 5
Private: No
Submitted By: ncryptor (ncryptor)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: audioop module - request to add a note

Initial Comment:
The audioop function lin2lin converts sample sizes of linear pcm fragments.
However, when converting to 8-bit, there is a pitfall (that wasted for me a few hours).
In some audio formats, such as .WAV files, 16 and 32 bit samples are signed, but 8 bit samples are unsigned. So when converting from 2 to 1 byte wide samples, you need to also add 128 to the result.
Example code:

new_frames = audioop.lin2lin(frames, old_width, new_width)
if 1 == new_width:
   new_frames = audioop.bias(new_frames, 1, 128)

the same, in reverse, has to be applied when converting from 8 to 16 or 32 bit width samples.

This wasted so much time for me and is hardly documented.


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>Comment By: Raymond Hettinger (rhettinger)
Date: 2007-04-19 01:45

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I will add a note.

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You can respond by visiting: 
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