A sequencer helper firmware for the Sol MIDI to CV converter module from Winterbloom

sol_seqpal.py

"""
##           Sol Seqpal v0.4.1       ##
## Leonora Tindall <nora@nora.codes> ##
##           Licensed GPLv.3         ##

A configurable sequencer helper for the Sol.

Defaults to:
3 CV/Gate channels on a/1, b/2, and c/3,
plus two percussion channels on 4 and d (abused as a trigger)

Each channel is re-triggered if a NOTE_ON message is recieved for that channel.

If using with ORCA, please recall that what is often called MIDI Ch 1 is really Ch 0,
and ORCA uses the real MIDI number.

Throughout the source code, I will refer to MIDI channels starting at 1.
"""

# ----------------- Config ---------------------------------------------------#

# Keys (numbers on the left) are MIDI channels starting at 1.
# Values (strings on the right) are pairs or singlets of CV channel and gate output,
# or just gate output. CV outputs (letters) can act as gate outputs but not vice versa.
# Appending "p", like "d4p", means scaling for the MODEL input of Plaits.
CHANNEL_CONFIG = {
    1: "a1",
    2: "b2",
    3: "c3",
    4: "d",
    5: "4"
}

# How many NOTE ON messages to buffer for multipress, so that keyboard players
# can more easily transition between notes as one might on a piano
# or polyphonic synthesizer.
# Set to 1 to disable this feature.
MULTIPRESS_LIMIT = 4

# The base MIDI note from which model changes are computed for Plaits.
# Based on the Beatstep Pro, check with your controller.
PLAITS_MODEL_BASE_NOTE = 36

# ----------------- Script ---------------------------------------------------#

import winterbloom_sol as sol
from winterbloom_sol import trigger
import winterbloom_smolmidi as midi

CHANNEL_NUMBERS = [1, 2, 3, 4]
CHANNEL_NAMES = ["a", "b", "c", "d"]

# Map of channel number to CV channel name.
CHANNEL_CV_NAME = {1: "a", 2: "b", 3: "c", 4: "d"}

# V/Oct multiplier for Plaits model voltage (1 note = 1 model)
PLAITS_MODEL_VOLTAGE_STEP = 5.0/16.0

class CvAsGateState:
    "Contains the state of a CV channel's trigger value, to be updated by Trigger.step()"
    def __init__(self):
        self.value = False
        self.trigger = trigger.Trigger(self)
        self.retrigger = trigger.Retrigger(self)

    def step(self):
        self.trigger.step()
        self.retrigger.step()
    
    def voltage(self):
        if self.value:
           return 5.0
        else:
           return 0.0

# Channel correspondance setup
channel_to_cv_channel = {}
channel_to_gate_channel = {}
scaled_channels = []
noteoff_buffers_by_channel = {}
pseudogates = {}

def exclusive(x):
    "Ensure x was not used in an existing channel"
    try:
        return not (x in channel_to_gate_channel \
            or x in channel_to_cv_channel) \
            or int(x) in channel_to_gate_channel
    except ValueError as e:
       return True

def valid_gate_channel(x):
    "Ensure x is valid as a trigger/gate channel"
    try:
        return x in CHANNEL_NAMES or int(x) in CHANNEL_NUMBERS
    except ValueError as e:
        return False

def int_if_possible(x):
    "Convert x to an int if possible, or leave as is"
    try:
        return int(x)
    except ValueError as e:
        return x

for k, v in CHANNEL_CONFIG.items():
    if 0 > len(v) > 3:
        raise ValueError("Channel config must be 1, 2, or 3 characters");
    if type(k) is not int or 1 > k > 16:
        raise ValueError("Channel number must be an integer between 1 and 16, inclusive.")

    if len(v) is 1:
        print(f"MIDI {k}: gate-only channel on {v}")
        if not valid_gate_channel(v):
            raise ValueError(f"Gate channel {v} not in {CHANNEL_NAMES} or {CHANNEL_NUMBERS}")
        if not exclusive(v):
            raise ValueError(f"Reuse of channel {v} in gate-only channel for {k}")
        channel_to_gate_channel[k] = int_if_possible(v)
    else:
        print(f"MIDI {k}: CV/gate channel on {v[0]} and {v[1]}")
        if v[0] not in CHANNEL_NAMES:
            raise ValueError(f"CV channel must be in {CHANNEL_NAMES}")
        if not valid_gate_channel(v[1]):
            raise ValueError(f"Gate channel {v[1]} not in {CHANNEL_NAMES} or {CHANNEL_NUMBERS}")
        if not exclusive(v):
            raise ValueError(f"Reuse of channel {v} in CV/gate channel for {k}") 
        channel_to_cv_channel[k] = v[0]
        noteoff_buffers_by_channel[k] = 0
        channel_to_gate_channel[k] = int_if_possible(v[1])
        if len(v) is 3 and v[2] == "p":
            print(f"MIDI {k}: CV scaled to Plaits model voltage")
            scaled_channels += [k]

for k, gate_channel in channel_to_gate_channel.items():
    if not type(gate_channel) is int:
        pseudogates[gate_channel] = CvAsGateState()

def loop(last, state, outputs):
    # Always update the state of the pseudogates 
    global channel_to_gate_channel, channel_to_cv_channel, pseudogates 

    for channel_name, pseudogate in pseudogates.items():
        pseudogate.step()
        outputs.set_cv(channel_name, pseudogate.voltage())
    
    # Check whether or not there's a new MIDI message to process.
    if state.message is last.message or state.message is None:
    	return # No change!

    
    # Messages without a channel are useless to us.
    if state.message.channel is None:
    	return # Don't care.
    ch = state.message.channel + 1 # MIDI channels are indexed from 0
    
    # MIDI handling for melodic channels.
    # Only NOTE_ON messages are used, in order to know the appropriate CV value.
    if ch in channel_to_cv_channel:
    	if state.message.type is midi.NOTE_ON:
            noteoff_buffers_by_channel[ch] = min([
                MULTIPRESS_LIMIT, noteoff_buffers_by_channel[ch] + 1
            ])
    	    if ch in scaled_channels:
    	        offset = state.message.data[0] - PLAITS_MODEL_BASE_NOTE
    	        voltage = PLAITS_MODEL_VOLTAGE_STEP * offset - (0.05)
    	        outputs.set_cv(channel_to_cv_channel[ch], voltage) 
    	    else:
                note = sol.note_to_volts_per_octave(state.message.data[0])
                outputs.set_cv(channel_to_cv_channel[ch], note)

    # MIDI handling for melodic and percussion channels.
    if ch in channel_to_gate_channel:
    	if state.message.type is midi.NOTE_ON:
            if channel_to_gate_channel[ch] in pseudogates:
                pseudogates[channel_to_gate_channel[ch]].retrigger.retrigger()
            else:
                outputs.retrigger_gate(channel_to_gate_channel[ch])
        elif state.message.type is midi.NOTE_OFF:
            # Decrement noteoff buffer and check if we should proceed
            actually_detrigger = True
            if ch in noteoff_buffers_by_channel:
                noteoff_buffers_by_channel[ch] = max([
                    0, noteoff_buffers_by_channel[ch] - 1
                ])
                if noteoff_buffers_by_channel[ch] > 0:
                    actually_detrigger = False
            if actually_detrigger:
                # De-trigger any associated gate, pseudo or real
                if channel_to_gate_channel[ch] in pseudogates:
                    pseudogates[channel_to_gate_channel[ch]].value = False
                else:
                    outputs.set_gate(channel_to_gate_channel[ch], False)

    # MIDI handling for "all notes off"
    if (state.message.type is midi.CC and state.message.data[0] is 0x7B):
        print("all notes off")
        for ch in channel_to_gate_channel:
            if ch in noteoff_buffers_by_channel:
                noteoff_buffers_by_channel[ch] = 0
            if channel_to_gate_channel[ch] in pseudogates:
                pseudogates[channel_to_gate_channel[ch]].value = False
            else:
                outputs.set_gate(channel_to_gate_channel[ch], False)


sol.run(loop)