I've recently had an idea to test some vibration-resonance problems by playing a set of sounds and detecting the vibrations in question. The glitch is, how to create a sound of desired frequency? I believe there is a lot of ways to solve this but having only a hammer (read Python) as my tool it looked like a nail ;-)
The idea is then to create a simple sine wave and play it back with a computer. My first try was with pygame module but the sound quality was poor and unsatisfactory.
If not playing sound directly one can write the wave to the file and then play the file with whatever means are suitable. This turned out to be the better way after all.
A search of the internet turned up this discussion of creating .wav files with Python. I've adopted the "minimal example" from there (written by Andrea Valle) to be usable with modern modules (it used obsolete Numeric and RandomArray modules). The code is not neat but it works well.
This code should work as intended and produce .wav files of given length and frequency. A few comments:
import numpy as N
def __init__(self, signal):
self.file = wave.open('test.wav', 'wb')
self.signal = signal
self.sr = 44100
self.file.setparams((1, 2, self.sr, 44100*4, 'NONE', 'noncompressed'))
# let's prepare signal
duration = 4 # seconds
samplerate = 44100 # Hz
samples = duration*samplerate
frequency = 440 # Hz
period = samplerate / float(frequency) # in sample points
omega = N.pi * 2 / period
xaxis = N.arange(int(period),dtype = N.float) * omega
ydata = 16384 * N.sin(xaxis)
signal = N.resize(ydata, (samples,))
ssignal = ''
for i in range(len(signal)):
ssignal += wave.struct.pack('h',signal[i]) # transform to binary
f = SoundFile(ssignal)
print 'file written'
a) if you need different sampling frequencies, just replace all 44100 numbers with desired sampling frequency;
b) the setparams command is relatively well described in wave doc in Python help, its fourth parameter (nframes) may probably be whatever number you want, the procedure is designed to write all data you sent to it;
c) the 16384 number seems to be a volume setting for .wav file, this value is near the maximum so only lowering the volume is possible from here;
d) wave.struct.pack('h', #) - this was tough to find but without this command the resulting file will not be correct (at least on Windows machines), I do not yet understand what it does...