audiothing.py

# https://deutsch.ucsd.edu/psychology/pages.php?i=201

import numpy as np
import scipy.io.wavfile
import scipy.special

f_s = 44100
duration = 10

note1 = 392
note2 = 784

dt = 1 / f_s
samples = []
phase = 0

# note1     ramp        note2       ramp
#                   ^ 0.25 sec
#                                           ^ 0.5 sec
interp_len = 0.010
def get_freq(t):
    tt = t % 0.5

    # errf
    if tt < 0.25 - interp_len:
        return note1
    elif tt < 0.25:
        relt = tt - (0.25 - interp_len)
        xx = relt / interp_len * 6 - 3
        yy = 0.5 - scipy.special.erf(xx) / 2
        return note1 * yy + note2 * (1 - yy)
    elif tt < 0.5 - interp_len:
        return note2
    else:
        relt = tt - (0.5 - interp_len)
        xx = relt / interp_len * 6 - 3
        yy = 0.5 - scipy.special.erf(xx) / 2
        return note2 * yy + note1 * (1 - yy)
    
    # linear
    # if tt < 0.25 - interp_len:
    #     return note1
    # elif tt < 0.25:
    #     return note1 + (note2-note1)*((tt-(0.25 - interp_len))/interp_len)
    # elif tt < 0.5 - interp_len:
    #     return note2
    # else:
    #     return note2 + (note1-note2)*((tt-(0.5 - interp_len))/interp_len)

for x in range(duration * f_s):
    t = x * dt
    freq = get_freq(t)

    y = 16383 * np.cos(phase)
    samples.append(y)

    phase += 2*np.pi * freq * dt

# xxx lol lmao
samples2 = []
for x in range(duration * f_s):
    t2 = int(x + 0.25*f_s) % (f_s * duration)
    samples2.append((samples[x], samples[t2]))

scipy.io.wavfile.write('test.wav', f_s, np.int16(samples2))