A very basic mono synthesizer using PyAudio and Matplotlib

mono-synth.py

# Installation
# Run `pip install pyaudio` first
# If that throws an error, you need to install a "wheel" first (pre-packaged binary)
# Follow the instructions here: https://stackoverflow.com/a/71073645/9655481
# e.g. I use Python 3.9.6 and installed the file "PyAudio‑0.2.11‑cp39‑cp39‑win_amd64.whl"
# from here: https://www.lfd.uci.edu/~gohlke/pythonlibs/#pyaudio

import time

import matplotlib.pyplot as plt
import numpy as np
import pyaudio
from matplotlib.widgets import Button, Slider

print('🎈 Started')


########################## Generate sound data ##################################

SAMPLE_RATE = 44100  # sample rate in hertz
FRAMES_PER_BUFFER = int(SAMPLE_RATE * 0.1)  # corresponds to 100ms
init_amplitude = 0.5  # signal amplitude scaler
init_frequency = 600  # signal frequency in hertz

FRAME_DURATION = 1 / SAMPLE_RATE
T = FRAMES_PER_BUFFER * FRAME_DURATION
t = np.linspace(0, T, FRAMES_PER_BUFFER)  # discrete signal time points

sound_data = {
    'clipped': None,
    'scaled': None
}


def update_sound_data(amplitude, frequency):
    signal = amplitude * np.sin(2 * np.pi * frequency * t)
    sound_data['clipped'] = signal.clip(-1, 1)
    # Convert from float [-1, +1] to int16 [-32768, +32767]
    sound_data['scaled'] = ((sound_data['clipped'] * 32767.5) - 0.5)\
        .astype(np.int16)


update_sound_data(init_amplitude, init_frequency)


################################ Plot ##########################################

fig, ax = plt.subplots()
line, = plt.plot(t, sound_data['clipped'])
ax.set_title('Synth')
ax.set_xlabel('Time [s]')
ax.set_xlim(left=0, right=10e-3)
ax.set_ylim(bottom=-2, top=2)

# Adjust the main plot to make room for the sliders
plt.subplots_adjust(left=0.25, bottom=0.25)

# Horizontal slider to control the frequency.
# TODO: logarithmic scale
ax_freq = plt.axes([0.25, 0.1, 0.65, 0.03])
freq_slider = Slider(
    ax=ax_freq,
    label='Frequency [Hz]',
    valmin=0.1,
    valmax=20000,
    valinit=init_frequency,
)

# Vertical slider to control the amplitude
ax_amp = plt.axes([0.1, 0.25, 0.0225, 0.63])
amp_slider = Slider(
    ax=ax_amp,
    label="Amplitude",
    valmin=0,
    valmax=3,
    valinit=init_amplitude,
    orientation="vertical"
)


def update_plot(event):
    update_sound_data(amp_slider.val, freq_slider.val)

    line.set_ydata(sound_data['clipped'])
    fig.canvas.draw_idle()


freq_slider.on_changed(update_plot)
amp_slider.on_changed(update_plot)

ax_reset = plt.axes([0.8, 0.025, 0.1, 0.04])
button = Button(ax_reset, 'Reset', hovercolor='0.975')


def reset(event):
    freq_slider.reset()
    amp_slider.reset()


button.on_clicked(reset)


################################ PyAudio #######################################

def get_data(in_data, frame_count, time_info, status):
    # sound_data gets changed dynamically
    out = sound_data['scaled']
    return (out.tobytes(), pyaudio.paContinue)


# PyAudio documentation: http://people.csail.mit.edu/hubert/pyaudio/
p = pyaudio.PyAudio()
stream = p.open(
    # int16 (number of bytes per audio frame)
    format=p.get_format_from_width(width=2),
    channels=1,  # mono
    rate=SAMPLE_RATE,
    frames_per_buffer=FRAMES_PER_BUFFER,
    output=True,
    stream_callback=get_data)
stream.start_stream()

plt.show()

# while stream.is_active():
#     # Sleep to keep the stream active, since
#     # the main thread must not terminate.
#     time.sleep(0.1)

stream.stop_stream()
stream.close()

p.terminate()

⚠ Right now, there's some crackling going on every time PyAudio reads from the next buffer. It even gets worse when you change the frequency. If anybody knows how to fix this, please let me know. The same problem occurs when you comment out all the lines for the Matplotlib GUI, so it's probably a PyAudio problem or rather I am doing something wrong with the buffer size.