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.
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.
Nope: The default is 8-bit unsigned samples, using one channel (mono), and an 8 kHz sampling rate. http://www.oreilly.de/catalog/multilinux/excerpt/ch14-05.htm Changing to rate = 8000 and sinusFloat = ... [0..rate-1] gives the expected output.
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
Claude -- http://claudiusmaximus.goto10.org