[Haskell-cafe] sound synthesis

[Thomas Girod]

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 
music/sound.

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 
expected.

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 
the interupt.

Thomas