[Haskell-cafe] sound synthesis
thomas at 0xc29.net
Fri May 2 05:58:54 EDT 2008
Hi there. Following this advice
(http://reddit.com/info/6hknz/comments/c03vdc7), I'm posting here.
Recently, I read a few articles about Haskell (and FP in general) and
I remember an article ranting about how lazy evaluation would be great
to do signal processing, but it was lacking real world example.
I tried to do a little something about it, even though I'm still an
haskell apprentice. So, here I come with a small bit of code, waiting
for your insights to improve it.
The task is to generate a sine wave and pipe it to /dev/dsp on my linux
box. There is probably a nicer way to make some noise, like using SDL
audio API bindings, but I didn't take the time to poke around this yet.
So here it is :
> module Main where
> import qualified Data.ByteString as B
> import Data.Word
> import IO (stdout)
> rate = 44100
> sinusFloat :: [Float]
> sinusFloat = map (\t -> (1 + sin (t*880*2*pi/rate)) / 2) [0..44099]
> sinusWord :: [Word8]
> sinusWord = map (\s -> floor (s * max)) sinusFloat
> where max = 255
> byte = B.pack sinusWord
> main = B.hPut stdout byte
It is supposed to generate a 880hz sine wav playing for one second, by
typing ./bin > /dev/dsp, assuming your soundcard has a 44100hz samplingrate.
/dev/dsp is supposed to receive its audio flux as an unsigned byte
stream, that's why I'm converting my sine from [-1;1] to [0;1] and then
to [0;255] Word8.
However, I must miss something because the sound does not have the right
frequency and is played too long. I guess the default sound format is
44100hz 16bits stereo, which would explain why it doesn't behave as
I'm wondering how I could convert a [Word16] to ByteString, and how I
could use lazy evaluation to generate an infinite sine that stops with
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