Simple Python Spectrograph with PyGame

Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

While thinking of ways to improve my QRSS VD high-definitions spectrograph software, I often wish I had a better way to display large spectrographs. Currently I’m using PIL (the Python Imaging Library) with TK and it’s slow as heck. I looked into the PyGame project, and it seems to be designed with speed in mind. I whipped-up this quick demo, and it’s a simple case audio spectrograph which takes in audio from your sound card and graphs it time vs. frequency. This method is far superior to the method I was using previously to display the data, because while QRSS VD can only update the entire GUI (500px by 8,000 px) every 3 seconds, early tests with PyGame suggests it can do it about 20 times a second (wow!). With less time/CPU going into the GUI, the program can be more responsivle and my software can be less of a drain.

Simple Spectrograph
import pygame
import numpy
import threading
import pyaudio
import scipy
import scipy.fftpack
import scipy.io.wavfile
import wave
rate=12000 #try 5000 for HD data, 48000 for realtime
soundcard=2
windowWidth=500
fftsize=512
currentCol=0
scooter=[]
overlap=5 #1 for raw, realtime - 8 or 16 for high-definition
def graphFFT(pcm):
	global currentCol, data
	ffty=scipy.fftpack.fft(pcm) #convert WAV to FFT
	ffty=abs(ffty[0:len(ffty)/2])/500 #FFT is mirror-imaged
	#ffty=(scipy.log(ffty))*30-50 # if you want uniform data
	print "MIN:t%stMAX:t%s"%(min(ffty),max(ffty))
	for i in range(len(ffty)):
		if ffty[i]<0: ffty[i]=0
		if ffty[i]>255: ffty[i]=255
	scooter.append(ffty)
	if len(scooter)<6:return
	scooter.pop(0)
	ffty=(scooter[0]+scooter[1]*2+scooter[2]*3+scooter[3]*2+scooter[4])/9
	data=numpy.roll(data,-1,0)
	data[-1]=ffty[::-1]
	currentCol+=1
	if currentCol==windowWidth: currentCol=0

def record():
	p = pyaudio.PyAudio()
	inStream = p.open(format=pyaudio.paInt16,channels=1,rate=rate,
						input_device_index=soundcard,input=True)
	linear=[0]*fftsize
	while True:
		linear=linear[fftsize/overlap:]
		pcm=numpy.fromstring(inStream.read(fftsize/overlap), dtype=numpy.int16)
		linear=numpy.append(linear,pcm)
		graphFFT(linear)

pal = [(max((x-128)*2,0),x,min(x*2,255)) for x in xrange(256)]
print max(pal),min(pal)
data=numpy.array(numpy.zeros((windowWidth,fftsize/2)),dtype=int)
#data=Numeric.array(data) # for older PyGame that requires Numeric
pygame.init() #crank up PyGame
pygame.display.set_caption("Simple Spectrograph")
screen=pygame.display.set_mode((windowWidth,fftsize/2))
world=pygame.Surface((windowWidth,fftsize/2),depth=8) # MAIN SURFACE
world.set_palette(pal)
t_rec=threading.Thread(target=record) # make thread for record()
t_rec.daemon=True # daemon mode forces thread to quit with program
t_rec.start() #launch thread
clk=pygame.time.Clock()
while 1:
	for event in pygame.event.get(): #check if we need to exit
		if event.type == pygame.QUIT:pygame.quit();sys.exit()
	pygame.surfarray.blit_array(world,data) #place data in window
	screen.blit(world, (0,0))
	pygame.display.flip() #RENDER WINDOW
	clk.tick(30) #limit to 30FPS