On Fri, 2 May 2008, Thomas Girod wrote:
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.
There are some 'real world examples', however speed is currently the
factor which limits the fun. Currently you get immediate results with the
SuperCollider interface or with the CSound interface of Haskore:
http://www.haskell.org/haskellwiki/Applications_and_libraries/Music_and_sound
Cf. Haskell Art mailing list:
http://lists.lurk.org/mailman/listinfo/haskell-art
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,
With Data.Binary.
and how I could use lazy evaluation to generate an infinite sine that
stops with the interupt.
So far I used a really silly way, but it worked for me so far: I start
'play' from SOX package and pipe my signal into it:
http://darcs.haskell.org/synthesizer/src/Sox/Play.hs
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