[Haskell-beginners] Processing data from microphone interactively

Martin Vlk martin at vlkk.cz
Sun Oct 25 19:52:28 UTC 2015

Hi Heinrich,
this is a great and very useful response, thanks!

I am working through my implementation details and I'll post the result
when I have it.


Heinrich Apfelmus:
> Hello Martin,
> in digital signal processing (DSP), audio samples are traditionally
> processed in *blocks*. Typical blocks sizes for real-time processing are
> 64, 128 or 256 bytes.
> The reason for this is that audio processing is a performance-sensitive
> task. If your code is too slow, then it cannot process all audio in time
> and there will be jitter. Typically, the operations that are applied to
> a single block are fairly limited (mixing, convolution, ...) and can be
> optimized into a tight loop, which you can then reuse as a "black box".
> In contrast, operations that act on blocks (envelopes, ...) are more
> open-ended and you would have to pay attention to optimizing them each
> and every time you write a program.
> This is related to the concepts of "audio rate" and "control rate". The
> former is the frequency at which audio is sampled, i.e. the frequency
> "within" a block, while the latter corresponds to more coarse-grained
> operations, that are approximately the same on every block.
> For you, this means that you probably want to call the `simpleRead`
> function with a block size of 128 and process each block individually
> before requesting the next. If individual processing proves too slow,
> you will have to use data structures that are closer to the machine, and
> call the `simpleReadRaw` function instead.
> Best regards,
> Heinrich Apfelmus
> -- 
> http://apfelmus.nfshost.com
> Martin Vlk wrote:
>> Hi,
>> I am looking at reading sound from a microphone and controlling some
>> other activity based on the sound data as they come. The motivation for
>> this is writing some interactive animated graphics controlled by
>> properties of the sound from mic.
>> I am using the pulseaudio-simple library to read sound from the computer
>> mic and that works fine. However the library function basically returns
>> sound samples as a list of predefined length and this is not well suited
>> for the kind of real-time processing I need.
>> I am looking for advice on what would be a good idiomatic way to design
>> such a program in Haskell.
>> From some research I am imagining I need something like the conduit
>> library to connect the sound data to other parts of my program, but I am
>> not sure how that would work or if it is a good idea in the first place.
>> Or should I use some of the FRP libraries for this purpose?
>> Or some other approach?
>> I'd appreciate some advice on the direction to take.
>> Many Thanks
>> Martin
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