[pygame] Sine Waves

[Kris Schnee <kschnee@xxxxxxxxxx>]

It's driving me nuts: why is this not producing a sine wave at the 
specified frequency? I get an ugly, rasping beep that doesn't sound at 
all like the sample at 
<http://www.sfu.ca/sonic-studio/handbook/Sine_Wave.html>, and sounds 
like a different frequency than the square waves produced by the 
function below. Calling "SineWave(100)[:220]" seems to show data that 
repeats every 220 cycles, ie. 100 times per second at the specified 
sample rate, yet it still doesn't sound right.

Kris



import pygame, math
from Numeric import *
SAMPLE_RATE = 22050 ## This many array entries == 1 second of sound.
pygame.init()

def SineWave(freq=1000,volume=100000,length=1):
    num_steps = length*SAMPLE_RATE
    s = []
    for n in range(num_steps):
        value = int(math.sin(n * freq * (6.28318/SAMPLE_RATE) * length 
)*volume)
        s.append( [value,value] )
    x_arr = array(s)
    return x_arr

def SquareWave(freq=1000,volume=100000,length=1):
    length_of_plateau = SAMPLE_RATE / (2*freq)
    s = []
    counter = 0
    state = 1
    for n in range(length*SAMPLE_RATE):
        if state == 1:
            value = volume
        else:
            value = -volume
        s.append( [value,value] )

        counter += 1
        if counter == length_of_plateau:
            counter = 0
            if state == 1:
                state = -1
            else:
                state = 1

    x_arr = array(s)
    return x_arr

def MakeSound(arr):
    return pygame.sndarray.make_sound(arr)

def PlaySquareWave(freq=1000):
    MakeSound(SquareWave(freq)).play()

def PlaySineWave(freq=1000):
    MakeSound(SineWave(freq)).play()