ComplexAmplitudeModulation_Q1.py

# filter_play_mic.py
# Record from micrphone, filter signal, play output to speaker

import pyaudio
import struct
import math
import cmath
import numpy as np
from math import exp
from math import expm1
# import wave

from myfunctions import clip16

WIDTH = 2           # Number of bytes per sample
CHANNELS = 1        # mono
RATE = 16000        # Sampling rate (frames/second)
DURATION = 10        # duration of processing (seconds)

N = DURATION*RATE   # N : Number of samples to process


I = cmath.sqrt(-1);
s0 = cmath.e**( I * 0.5 * math.pi * 0 );
s1 = cmath.e**( I * 0.5 * math.pi * 1 );
s2 = cmath.e**( I * 0.5 * math.pi * 2 );
s3 = cmath.e**( I * 0.5 * math.pi * 3 );
s4 = cmath.e**( I * 0.5 * math.pi * 4 ); 
# Difference equation coefficients
b0 =  0.008442692929081*s0
b2 = -0.016885385858161*s2
b4 =  0.008442692929081*s4

# a0 =  1.000000000000000
a1 = -3.580673542760982*s1
a2 =  4.942669993770672*s2
a3 = -3.114402101627517*s3
a4 =  0.757546944478829*s4

# Initialization
x1 = 0.0
x2 = 0.0
x3 = 0.0
x4 = 0.0
y1 = 0.0
y2 = 0.0
y3 = 0.0
y4 = 0.0





p = pyaudio.PyAudio()

# Open audio stream
stream = p.open(format = p.get_format_from_width(WIDTH),
                channels = CHANNELS,
                rate = RATE,
                input = True,
                output = True)

print("**** Start ****")

for n in range(0, N):

    # Get one frame from audio input (microphone)
    input_string = stream.read(1)

    # Convert binary string to tuple of numbers
    input_tuple = struct.unpack('h', input_string)

    # Convert one-element tuple to number
    input_value = input_tuple[0]

    # Set input to difference equation
    x0 = input_value

    # Difference equation
    y0 = b0*x0 + b2*x2 + b4*x4 - a1*y1 - a2*y2 - a3*y3 - a4*y4 
    #print y0

    f1 = 400;           #% Modulation frequency
    #output_value = y0 * math.cos(2.0*math.pi*f1*n/RATE)

    g = y0 * cmath.exp((I * 2.0 * math.pi * f1 * n/RATE ));
    #print g;
    y = g.real;
   


    # Delays
    x4 = x3
    x3 = x2
    x2 = x1
    x1 = x0
    y4 = y3
    y3 = y2
    y2 = y1
    y1 = y0

    # Compute output value
    #output_value = clip16(y0)    # Number



    output_value = clip16(y)   # Bypass filter (listen to input directly)

    # Convert output value to binary string
    output_string = struct.pack('h', 6*output_value)  

    # Write binary string to audio stream
    stream.write(output_string)                     

print("**** Done ****")

stream.stop_stream()
stream.close()
p.terminate()