super_simple_synth.py

import math
import pyaudio
import itertools
import numpy as np
from pygame import midi

BUFFER_SIZE = 256
SAMPLE_RATE = 44100
NOTE_AMP = 0.1

# -- HELPER FUNCTIONS --
def get_sin_oscillator(freq=55, amp=1, sample_rate=SAMPLE_RATE):
    increment = (2 * math.pi * freq) / sample_rate
    return (
        math.sin(v) * amp * NOTE_AMP for v in itertools.count(start=0, step=increment)
    )


def get_samples(notes_dict, num_samples=BUFFER_SIZE):
    return [
        sum([int(next(osc) * 32767) for _, osc in notes_dict.items()])
        for _ in range(num_samples)
    ]


# -- INITIALIZION --
midi.init()
default_id = midi.get_default_input_id()
midi_input = midi.Input(device_id=default_id)

stream = pyaudio.PyAudio().open(
    rate=SAMPLE_RATE,
    channels=1,
    format=pyaudio.paInt16,
    output=True,
    frames_per_buffer=BUFFER_SIZE,
)

# -- RUN THE SYNTH --
try:
    print("Starting...")
    notes_dict = {}
    while True:
        if notes_dict:
            # Play the notes
            samples = get_samples(notes_dict)
            samples = np.int16(samples).tobytes()
            stream.write(samples)

        if midi_input.poll():
            # Add or remove notes from notes_dict
            for event in midi_input.read(num_events=16):
                (status, note, vel, _), _ = event
                if status == 0x80 and note in notes_dict:
                    del notes_dict[note]
                elif status == 0x90 and note not in notes_dict:
                    freq = midi.midi_to_frequency(note)
                    notes_dict[note] = get_sin_oscillator(freq=freq, amp=vel / 127)

except KeyboardInterrupt as err:
    midi_input.close()
    stream.close()
    print("Stopping...")