Simple Pygame Sound at Frequency

Question

How can I create a 440 Hz sound that plays smoothly forever using Pygame sound? I suppose this should be simple enough, but I don't want to use stupid files to complete the task. The ultimate goal of this is to play a note while the key is held, as I asked in another question. Any help would be greatly appreciated since I spent a lot of time searching for an answer to this question.

Answer 1

What is 440 Hz sound? There are many types of waves at 440 Hz: sine, saw, square, etc. You can have a flute playing A, and that too can count.

Assuming you need a sine wave, it looks like you can create a sound object using pygame.sndarray.samples . (I have not tested this). You can create patterns with:

 samples = [math.sin(2.0 * math.pi * frequency * t / sample_rate) for t in xrange(0, duration_in_samples)] 

This, I hope, is the basic sinusoidal material. frequency - the desired frequency, Hz. sample_rate - the number of samples / sec in the generated sound: a typical value is 44100 Hz. duration_in_samples - audio length. (5 * 44100 == 5 seconds if your sound has a sampling frequency of 44100 Hz.)

It looks like you might have to convert the samples to numpy.array before moving on to pygame.sndarray.samples . The docs show that the sound should match the format returned by pygame.mixer.get_init , so configure the samples accordingly, but this is the main idea. ( mixer.get_init will tell you the sample_rate variable sample_rate and whether you need to consider stereo, and if you need to adjust the wave amplitude or shift it.)

Make samples an integer of wavelengths and it should loop.

Answer 2

After getting too much “ValueError: The depth of the array should match the number of mixer channels” and other similar errors, I found this working example http://www.mail-archive.com/ [e-mail] /msg16140.html . It correctly generates a multidimensional 16-bit integer array that works with a stereo mixer. The minimum working example below is mainly taken from the previous link with the necessary pygame bits. In Python 2.7.2 with pygame.ver '1.9.1release.

In this example, a 440 Hz tone from one speaker and a 550 Hz tone from another speaker will be played in the stereo setting. After a short game with a duration, I found that audible clicks will appear in the sound loop if you set the “duration” variable to anything other than an integer.

 import pygame from pygame.locals import * import math import numpy size = (1366, 720) bits = 16 #the number of channels specified here is NOT #the channels talked about here http://www.pygame.org/docs/ref/mixer.html#pygame.mixer.get_num_channels pygame.mixer.pre_init(44100, -bits, 2) pygame.init() _display_surf = pygame.display.set_mode(size, pygame.HWSURFACE | pygame.DOUBLEBUF) duration = 1.0 # in seconds #freqency for the left speaker frequency_l = 440 #frequency for the right speaker frequency_r = 550 #this sounds totally different coming out of a laptop versus coming out of headphones sample_rate = 44100 n_samples = int(round(duration*sample_rate)) #setup our numpy array to handle 16 bit ints, which is what we set our mixer to expect with "bits" up above buf = numpy.zeros((n_samples, 2), dtype = numpy.int16) max_sample = 2**(bits - 1) - 1 for s in range(n_samples): t = float(s)/sample_rate # time in seconds #grab the x-coordinate of the sine wave at a given time, while constraining the sample to what our mixer is set to with "bits" buf[s][0] = int(round(max_sample*math.sin(2*math.pi*frequency_l*t))) # left buf[s][1] = int(round(max_sample*0.5*math.sin(2*math.pi*frequency_r*t))) # right sound = pygame.sndarray.make_sound(buf) #play once, then loop forever sound.play(loops = -1) #This will keep the sound playing forever, the quit event handling allows the pygame window to close without crashing _running = True while _running: for event in pygame.event.get(): if event.type == pygame.QUIT: _running = False break pygame.quit()