[Tutor] Chord player

[Mr Gerard Kelly]

I want to thank Emmanuel from the tutor mailing list for showing me a
piece of code that let me do exactly what I wanted - making Python play
a chord from a input of frequencies. I only needed to make a few
adjustments.

The code (below) uses Numeric. Emmanuel said that Numeric is out of date
and should be replaced everywhere by numpy. When I do that there is no
error message but the code doesn't play any sound. So I'm keeping
Numeric in there (although I read somewhere that Python automatically
converts Numeric to numpy anyway).

I did have one problem, which is when you play a chord, you hear a
clipping sound every second. I assume that is because of this line:

def sine_array(hz, peak, n_samples = sample_rate):
#Compute N samples of a sine wave with given frequency and peak
amplitude (defaults to one second).
return Numeric.resize(sine_array_onecycle(hz, peak), (n_samples,))

I thought I could get rid of the clipping noise by making it return more
samples than just for one second. For instance if I put in 2*(n_samples)
instead of the default sample_rate value, it might make the clipping
sound come every 2 seconds etc. However, I have found that if I put in
any other value other than the default value, it cannot calculate. The
dimensions are wrong or there is a memory problem or something. I'm not
sure how the resize method works and I was wondering if it is actually
possible to fix this problem this way.

Here's the whole code:


***

import pygame, time, random, Numeric, pygame, pygame.sndarray
sample_rate = 44100

def sine_array_onecycle(hz, peak):
  #Compute one cycle of an N-Hz sine wave with given peak amplitude
  length = sample_rate / float(hz)
  omega = Numeric.pi * 2 / length
  xvalues = Numeric.arange(int(length)) * omega
  return (peak * Numeric.sin(xvalues)).astype(Numeric.Int16)

def sine_array(hz, peak, n_samples = sample_rate):
  #Compute N samples of a sine wave with given frequency and peak
amplitude (defaults to one second).

  return Numeric.resize(sine_array_onecycle(hz, peak), (n_samples,))

def waves(*chord):
  #Compute the harmonic series for a vector of frequencies
  #Create square-like waves by adding odd-numbered overtones for each
fundamental tone in the chord
  #the amplitudes of the overtones are inverse to their frequencies.
  h=9
  ot=3
  harmonic=sine_array(chord[0],4096)
  while (ot<h):
      if (ot*chord[0])<(sample_rate/2):
        harmonic=harmonic+(sine_array(chord[0]*ot, 4096/(2*ot)))
      else: 
        harmonic=harmonic+0
      ot+=2
  for i in range(1,len(chord)):
    harmonic+=(sine_array(chord[i], 4096))
  
    
    if (ot*chord[i])<(sample_rate/2):
      harmonic=harmonic+(sine_array(chord[i]*ot, 4096/(2*ot)))
    else: 
      harmonic=harmonic+0
    ot+=2    
  return harmonic

def play_for(sample_array, ms):
  #Play the sample array as a sound for N ms.
  pygame.mixer.pre_init(sample_rate, -16, 1) # 44.1kHz, 16-bit signed, mono
  pygame.init()
  sound = pygame.sndarray.make_sound(sample_array)
  sound.play(-1)
  pygame.time.delay(ms)
  sound.stop()

def main():
  #Play a single sine wave, followed by a chord with overtones.
  
  pygame.mixer.pre_init(sample_rate, -16, 1) # 44.1kHz, 16-bit signed, mono
  pygame.init()
  play_for(sine_array(440, 4096), 2500)
  play_for(waves(440,550,660,770,880), 5000)


if __name__ == '__main__': main()


***

Thanks for having a look!

Gerard.

Gerard Kelly wrote:
> Hi everyone, I'm a python noob but I have an ambitious (for me) goal: I
> want to make a simple program that allows you to hear combinations of
> notes according to a vector of frequencies.
>
> Does anybody know any module that allows you to input a frequency in Hz
> and returns a sound with that frequency, and lets you do that with
> multiple frequencies, so that you can build chords?


The recipe linked below plays sounds composed of a fundamental and a few
harmonics. It requires Pygame and NumPy.

http://osdir.com/ml/culture.people.kragen.hacks/2007-11/msg00000.html

It is out of date, though. I had to change 'Numeric' to 'numpy' and 'Int16'
to 'int16' to get it to work.  Moreover NumPy doesn't seem to work with
Python 2.6.


You can also use TkSnack (http://www.speech.kth.se/snack/). Check the
example named 'notescale' that comes with the module: it defines a function
that receives a frequency as an input and plays a sound; there is also a
graphical interface.


Regards,
Emmanuel

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