Operation Manual

Experiments in Python

Notes:

Making a noise

Graphics are all well and good, but if we are going to create true multimedia

software then we’re going to need to master audio output as well. Let’s see if we

can add some sounds to our programs.

import numpy

import wave

import pygame

# sample rate of a WAV le

SAMPLERATE = 44100 # Hz

def createSignal(frequency, duration):

samples = int(duration*SAMPLERATE)

period = SAMPLERATE / frequency # in sample points

omega = numpy.pi * 2 / period

xaxis = numpy.arange(samples, dtype=numpy.oat) * omega

yaxis = 16384 * numpy.sin(xaxis)

# 16384 is maximum amplitude (volume)

return ya xis.asty p e('int16').t o s t r i n g()

def createWAVFile(lename, signal):

le = wave.open(lename, 'wb')

le.setparams((1, 2, SAMPLERATE, len( s i g n a l ), 'NONE',

'noncompressed'))

le.writeframes(signal)

le.close()

def playWAVFile(  l e n a m e ):

pygame.mixer.init()

sound = pygame.mixer.Sound(lename)

so u n d.play()

# wait for sound to stop playing

while p y g a m e . m i x e r.g e t _ b u s y( ):

pass

# main program starts here

lename = '/tmp/440hz.wav'

signal = createSignal(frequency=440, duration=4)

createWAVFile(lename, signal)

playWAVFile(lename)

Playing sounds on a computer simply means taking data from a ﬁle, converting it

to waveform data and then sending that to hardware that converts the waveform

into an electrical signal, which then goes to an ampliﬁer and loudspeaker.

On the Raspberry Pi, PyGame can be used to play sounds from a ﬁle. Rather than

provide a ﬁle with some sound on it, we will generate a ﬁle with the data within it

to play sound. You probably know that sound is actually the compression and

rarefaction (stretching) of air to cause your eardrum to move.