A Hard Day's Night first chord with AudioLazy + PyAudio (Based on an example from the Coursera DSP course)

a_hard_night_chord_audiolazy.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Created on Thu Oct 10 15:29:33 2013
# @author: Danilo J. S. Bellini
"""
A Hard Day's Night first chord with AudioLazy + PyAudio
"""

from audiolazy import (white_noise, rint, freq_to_lag, zeros, comb, sHz,
                       str2freq, AudioIO)

def truncated_karplus_strong(freq, tau, memory=white_noise):
    """
    Karplus-Strong algorithm.

    Parameters
    ----------
    freq:
      Frequency, in rad/sample.
    tau:
      Time, in samples, until decaying from 1 to 1/e in amplitude (approx.
      -8.686 dB). You can find ``tau`` from half-power decay duration with
      ``tau = halfpower_decay * dB20(1/e) / dB10(.5)``.
    memory:
      Past memory in the Karplus-Strong comb filter. Original algorithm
      proposes random data (white noise). Defaults to uniformly distributed
      white noise from -1 to 1.

    Returns
    -------
    A Stream object with the played tune.

    Note
    ----
    This function truncates the frequency to the nearest integer lag. Decay
    time (in samples) doesn't need to be integer.

    """
    rounded_lag = rint(freq_to_lag(freq))
    filt = comb.tau(rounded_lag, tau)
    return filt(zeros(), memory=memory)


# Initialization
rate = 48000
s, Hz = sHz(rate)
ms = 1e-3 * s

# Synth model parameters
tau = 626.7 * ms # 217.2 * ms half-power decay
                 # Original tau was approx. 626.698490797 * ms
memory = white_noise(low=0, high=1) # No negative value: DC level isn't zero
ks = lambda freq: truncated_karplus_strong(freq, tau=tau, memory=memory)

# Synthesizes the chord
pitches = "D2 D3 F3 G3 F4 A4 C5 G5"
gains = [1.2, 3.0, 1.0, 2.2, 1.0, 1.0, 1.0, 3.5] # Per note
freqs = str2freq(pitches.split())
notes = (gain * ks(freq * Hz) for freq, gain in zip(freqs, gains))
snd = sum(notes) / sum(gains)

# Plays it for some seconds
with AudioIO(True) as player:
    player.play(snd.take(4 * s), rate=rate)