Create cpx-basic-synth.py

Author: TheKitty

Circuit_Playground_Express_USB_MIDI/cpx-basic-synth.py

@@ -0,0 +1,217 @@
+### cpx-basic-synth v1.4
+### CircuitPython (on CPX) synth module using internal speaker
+### Velocity sensitive monophonic synth
+### with crude amplitude modulation (cc1) and choppy pitch bend
+
+### Tested with CPX and CircuitPython and 4.0.0-beta.7
+
+### Needs recent adafruit_midi module
+
+### copy this file to CPX as code.py
+
+### MIT License
+
+### Copyright (c) 2019 Kevin J. Walters
+
+### Permission is hereby granted, free of charge, to any person obtaining a copy
+### of this software and associated documentation files (the "Software"), to deal
+### in the Software without restriction, including without limitation the rights
+### to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+### copies of the Software, and to permit persons to whom the Software is
+### furnished to do so, subject to the following conditions:
+
+### The above copyright notice and this permission notice shall be included in all
+### copies or substantial portions of the Software.
+
+### THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+### IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+### FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+### AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+### LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+### OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+### SOFTWARE.
+
+import array
+import time
+import math
+
+import digitalio
+import audioio
+import board
+import usb_midi
+import neopixel
+
+import adafruit_midi
+
+from adafruit_midi.midi_message     import note_parser
+
+from adafruit_midi.note_on          import NoteOn
+from adafruit_midi.note_off         import NoteOff
+from adafruit_midi.control_change   import ControlChange
+from adafruit_midi.pitch_bend       import PitchBend
+
+# Turn the speaker on
+speaker_enable = digitalio.DigitalInOut(board.SPEAKER_ENABLE)
+speaker_enable.direction = digitalio.Direction.OUTPUT
+speaker_on = True
+speaker_enable.value = speaker_on
+
+dac = audioio.AudioOut(board.SPEAKER)
+
+# 440Hz is the standard frequency for A4 (A above middle C)
+# MIDI defines middle C as 60 and modulation wheel is cc 1 by convention
+A4refhz = const(440)
+midi_note_C4 = note_parser("C4")
+midi_note_A4 = note_parser("A4")
+midi_cc_modwheel = const(1)
+twopi = 2 * math.pi
+
+# A length of 12 will make the sawtooth rather steppy
+sample_len = 12
+base_sample_rate = A4refhz * sample_len
+max_sample_rate = 350000  # a CPX / M0 DAC limitation
+
+midpoint = 32768
+
+# A sawtooth function like math.sin(angle)
+# 0 returns 1.0, pi returns 0.0, 2*pi returns -1.0
+def sawtooth(angle):
+    return 1.0 - angle % twopi / twopi * 2
+
+# make a sawtooth wave between +/- each value in volumes
+# phase shifted so it starts and ends near midpoint
+# "H" arrays for RawSample looks more memory efficient
+# see https://forums.adafruit.com/viewtopic.php?f=60&t=150894
+def waveform_sawtooth(length, waves, volumes):
+    for vol in volumes:
+        waveraw = array.array("H",
+                              [midpoint +
+                               round(vol * sawtooth((idx + 0.5) / length
+                                                    * twopi
+                                                    + math.pi))
+                               for idx in list(range(length))])
+        waves.append((audioio.RawSample(waveraw), waveraw))
+
+# Make some square waves of different volumes volumes, generated with
+# n=10;[round(math.sqrt(x)/n*32767*n/math.sqrt(n)) for x in range(1, n+1)]
+# square root is for mapping velocity to power rather than signal amplitude
+# n=15 throws MemoryError exceptions when a note is played :(
+waveform_by_vol = []
+waveform_sawtooth(sample_len,
+                  waveform_by_vol,
+                  [10362, 14654, 17947, 20724, 23170,
+                   25381, 27415, 29308, 31086, 32767])
+
+# brightness 1.0 saves memory by removing need for a second buffer
+# 10 is number of NeoPixels on CPX
+numpixels = const(10)
+pixels = neopixel.NeoPixel(board.NEOPIXEL, numpixels, brightness=1.0)
+
+# Turn NeoPixel on to represent a note using RGB x 10
+# to represent 30 notes - doesn't do anything with pitch bend
+def noteLED(pix, pnote, pvel):
+    note30 = (pnote - midi_note_C4) % (3 * numpixels)
+    pos = note30 % numpixels
+    r, g, b = pix[pos]
+    if pvel == 0:
+        brightness = 0
+    else:
+        # max brightness will be 32
+        brightness = round(pvel / 127 * 30 + 2)
+    # Pick R/G/B based on range within the 30 notes
+    if note30 < 10:
+        r = brightness
+    elif note30 < 20:
+        g = brightness
+    else:
+        b = brightness
+    pix[pos] = (r, g, b)
+
+# Calculate the note frequency from the midi_note with pitch bend
+# of pb_st (float) semitones
+# Returns float
+def note_frequency(midi_note, pb_st):
+    # 12 semitones in an octave
+    return A4refhz * math.pow(2, (midi_note - midi_note_A4 + pb_st) / 12.0)
+
+midi_channel = 1
+midi = adafruit_midi.MIDI(midi_in=usb_midi.ports[0],
+                          in_channel=midi_channel-1)
+
+# pitchbendrange in semitones - often 2 or 12
+pb_midpoint = 8192
+pitch_bend_multiplier = 2 / pb_midpoint
+pitch_bend_value = pb_midpoint  # mid point - no bend
+
+wave = []  # current or last wave played
+last_note = None
+
+# Amplitude modulation frequency in Hz
+am_freq = 16
+mod_wheel = 0
+
+# Read any incoming MIDI messages (events) over USB
+# looking for note on, note off, pitch bend change
+# or control change for control 1 (modulation wheel)
+# Apply crude amplitude modulation using speaker enable
+while True:
+    msg = midi.receive()
+    if isinstance(msg, NoteOn) and msg.velocity != 0:
+        last_note = msg.note
+        # Calculate the sample rate to give the wave form the frequency
+        # which matches the midi note with any pitch bending applied
+        pitch_bend = (pitch_bend_value - pb_midpoint) * pitch_bend_multiplier
+        note_freq = note_frequency(msg.note, pitch_bend)
+        note_sample_rate = round(base_sample_rate * note_freq / A4refhz)
+
+        # Select the wave with volume for the note velocity
+        # Value slightly above 127 together with int() maps the velocities
+        # to equal intervals and avoids going out of bound
+        wave_vol = int(msg.velocity / 127.01 * len(waveform_by_vol))
+        wave = waveform_by_vol[wave_vol]
+
+        if note_sample_rate > max_sample_rate:
+            note_sample_rate = max_sample_rate
+        wave[0].sample_rate = note_sample_rate  # must be integer
+        dac.play(wave[0], loop=True)
+
+        noteLED(pixels, msg.note, msg.velocity)
+
+    elif (isinstance(msg, NoteOff) or
+          isinstance(msg, NoteOn) and msg.velocity == 0):
+        # Our monophonic "synth module" needs to ignore keys that lifted on
+        # overlapping presses
+        if msg.note == last_note:
+            dac.stop()
+            last_note = None
+
+        noteLED(pixels, msg.note, 0)  # turn off NeoPixel
+
+    elif isinstance(msg, PitchBend):
+        pitch_bend_value = msg.pitch_bend  # 0 to 16383
+        if last_note is not None:
+            pitch_bend = (pitch_bend_value - pb_midpoint) * pitch_bend_multiplier
+            note_freq = note_frequency(last_note, pitch_bend)
+            note_sample_rate = round(base_sample_rate * note_freq / A4refhz)
+            if note_sample_rate > max_sample_rate:
+                note_sample_rate = max_sample_rate
+            wave[0].sample_rate = note_sample_rate  # must be integer
+            dac.play(wave[0], loop=True)
+
+    elif isinstance(msg, ControlChange):
+        if msg.control == midi_cc_modwheel:
+            mod_wheel = msg.value  # msg.value is 0 (none) to 127 (max)
+
+    if mod_wheel > 0:
+        t1 = time.monotonic() * am_freq
+        # Calculate a form of duty_cycle for enabling speaker for crude
+        # amplitude modulation. Empirically the divisor needs to greater
+        # than 127 as can't hear much when speaker is off more than half
+        # 220 works reasonably well
+        new_speaker_on = (t1 - int(t1)) > (mod_wheel / 220)
+    else:
+        new_speaker_on = True
+
+    if speaker_on != new_speaker_on:
+        speaker_enable.value = new_speaker_on
+        speaker_on = new_speaker_on