The audioop module contains some useful operations on sound fragments.
It operates on sound fragments consisting of signed integer samples of
8, 16 or 32 bits wide, stored in Python strings. This is the same
format as used by the al and sunaudiodev modules. All
scalar items are integers, unless specified otherwise.
A few of the more complicated operations only take 16-bit samples, otherwise the sample size (in bytes) is always a parameter of the operation.
The module defines the following variables and functions:
Note that operations such as mul or max make no
distinction between mono and stereo fragments, i.e. all samples are
treated equal. If this is a problem the stereo fragment should be split
into two mono fragments first and recombined later. Here is an example
of how to do that:
verbatim167#
If you use the ADPCM coder to build network packets and you want your
protocol to be stateless (i.e. to be able to tolerate packet loss)
you should not only transmit the data but also the state. Note that
you should send the initial state (the one you passed to
lin2adpcm) along to the decoder, not the final state (as returned by
the coder). If you want to use struct to store the state in
binary you can code the first element (the predicted value) in 16 bits
and the second (the delta index) in 8.
The ADPCM coders have never been tried against other ADPCM coders, only against themselves. It could well be that I misinterpreted the standards in which case they will not be interoperable with the respective standards.
The find... routines might look a bit funny at first sight.
They are primarily meant for doing echo cancellation. A reasonably
fast way to do this is to pick the most energetic piece of the output
sample, locate that in the input sample and subtract the whole output
sample from the input sample:
verbatim168#