karplus-strong-example.py

#!/usr/bin/env python3

#--------------------------------------------------------------------------------
# SignalFlow: Karplus-Strong string synthesis.
# https://en.wikipedia.org/wiki/Karplus%E2%80%93Strong_string_synthesis
#--------------------------------------------------------------------------------

from signalflow import *
import numpy as np
import random

def main():
    feedback = 0.99
    note_interval = 0.125

    #--------------------------------------------------------------------------------
    # Karplus-Strong synthesis requires a short delay line whose delay time
    # is 1/F of the synthesized frequency. Because SignalFlow reads and writes
    # buffers (including the feedback notes) on a block-by-block basis, this delay
    # time can only be as short as the graph's global block size, so set a small
    # block size so we can render a reasonable range of frequencies.
    #--------------------------------------------------------------------------------
    config = AudioGraphConfig()
    config.output_buffer_size = 128
    graph = AudioGraph(config=config, start=True)
    graph.poll(2)

    #--------------------------------------------------------------------------------
    # Short burst of noise to excite the delay line
    #--------------------------------------------------------------------------------
    excitation_buf = Buffer(np.random.uniform(-1, 1, 256))
    player = BufferPlayer(excitation_buf)

    #--------------------------------------------------------------------------------
    # Set up a buffer that will be used as the feedback line's delay ringbuffer.
    #--------------------------------------------------------------------------------
    feedback_buf = Buffer(1, 2048)
    feedback_reader = FeedbackBufferReader(feedback_buf)

    #--------------------------------------------------------------------------------
    # Pick a random frequency each time a note is played. If `clock` is non-zero,
    # RandomExponential will generate a random signal at audio rate. Zero it and
    # it will only generate when triggered.
    #--------------------------------------------------------------------------------
    random_frequency = RandomExponential(1, 6, clock=0)
    rounded_frequency = Round(random_frequency) * 50

    #--------------------------------------------------------------------------------
    # Write to the feedback buffer.
    #--------------------------------------------------------------------------------
    output = SVFilter(player * 0.5 + feedback_reader, "low_pass", 4000)
    feedback_writer = FeedbackBufferWriter(feedback_buf, output * feedback, 1/rounded_frequency)

    #--------------------------------------------------------------------------------
    # Play the rendered output as a stereo signal.
    # Note that the feedback_writer also needs to be "played". This is because
    # the audio synthesis works by pulling each of the Graph's outputs in turn,
    # and recursing through each of their inputs. As the FeedbackBufferWriter
    # is not an input to any other node, it must be processed explicitly.
    #--------------------------------------------------------------------------------
    graph.play([output, output])
    graph.play(feedback_writer)

    #--------------------------------------------------------------------------------
    # Periodically, re-generate the excitation buffer and generate a new note.
    #--------------------------------------------------------------------------------
    while True:
        graph.wait(note_interval)
        excitation_buf.fill(lambda n: random.uniform(-1, 1))
        player.trigger()
        random_frequency.trigger()

if __name__ == "__main__":
    main()