real-time harmonic synthesis with PyGame and Numeric in Python

Kragen Javier Sitaker kragen at pobox.com
Thu Nov 1 20:42:34 EDT 2007


#!/usr/bin/python
"""Demonstrate harmonic synthesis in Python.

Python itself is slow enough that if we had to execute multiple Python
bytecodes per sample, we'd probably not keep up, even on modern
hardware.  But with Numerical Python ("Numeric") we can run the inner
loops of harmonic synthesis in C and have "NSL" --- no stinking loops!

And PyGame is awesome in that (a) it's easy to get stuff up and
running quickly and (b) it comes with an interface to Numeric.

"""

import pygame, time, random, Numeric, pygame, pygame.sndarray
sample_rate = 44100

def sine_array_onecycle(hz, peak):
    "Compute one cycle of an N-Hz sine wave with given peak amplitude."
    length = sample_rate / float(hz)
    omega = Numeric.pi * 2 / length
    xvalues = Numeric.arange(int(length)) * omega
    return (peak * Numeric.sin(xvalues)).astype(Numeric.Int16)
def sine_array(hz, peak, n_samples = sample_rate):
    """Compute N samples of a sine wave with given frequency and peak amplitude.

    Defaults to one second."""
    return Numeric.resize(sine_array_onecycle(hz, peak), (n_samples,))
def second_harmonic(hz):
    "Compute a wave with a strong second harmonic."
    return sine_array(hz, 16384) + sine_array(hz * 2, 16384)
def brass(hz):
    "Compute a sound with some odd harmonics.  Doesn't really sound brassy."
    return sum([sine_array(hz, 4096),
                sine_array(hz * 3, 4096),
                sine_array(hz * 5, 4096)])
def play_for(sample_array, ms):
    "Play given samples, as a sound, for N ms."
    sound = pygame.sndarray.make_sound(sample_array)
    sound.play(-1)
    pygame.time.delay(ms)
    sound.stop()
    
def main():
    "Play some funky sounds, as a demo."
    pygame.mixer.pre_init(sample_rate, -16, 1) # 44.1kHz, 16-bit signed, mono
    pygame.init()
    play_for(sine_array(440, 4096), 500)
    play_for(second_harmonic(440), 500)
    play_for(brass(440), 500)

if __name__ == '__main__': main()


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