Variation/continuation of a theme from this live session: https://twitter.com/forthcharlie/status/621101740046319616

CharlieREPL Livecoding Session 20150715

Beginnings of my polyphonic synth project for the amazing STM32F401 discovery board (£10), currently supporting:

22.05kHz sample rate (variable)
3 stereo voices, each with 2 oscillators (L/R)
4 oscillator types (sin, rect, saw, noise)
written in C11 and ASM using HAL & BSP audio drivers

Planned features:
- Filters
- FM osc
- Wavetables / sample banks
- Gyroscope for gestural control
- Forth frontend (via USB) for livecoding
- MIDI control

http://uk.rs-online.com/web/p/processor-microcontroller-development-kits/7892819/

stm32f401 - 3-polysynth

- optimized polyphony handling to squeeze in a 4th voice
- added LFO support (2 per voice: 1 pitch, 1 envolope mod, any waveform)

In this demo, the slow LFO controls attack & decay time of each note...

stm32f401 - 4-polysynth + lfo

Same as https://soundcloud.com/forthcharlie/stm32f401-4-polysynth-lfo, but using sin oscillators instead of rect osc...

stm32f401 - 4-polysynth + lfo (sin osc version)

Today I added 2 global LFOs for pitch & envelope modulation, as well as added a fixed length stereo delay line (maxed out the avaiable 64KB RAM, might switch to mono delay).

There's also a new additive oscillator with up to 4 configurable harmonics (this demo only uses 2)

stm32f401 - 4-polysynth + additive osc + delay

Same as previous track, but using saw & rect oscillators

stm32f401 - 4-polysynth + saw/rect + delay

Added some features to generative semi-random sequencer (Mersenne-Twister Tiny), now with key changes on predefined secondary scale. Also switched to mono delay to achieve longer periods (due to RAM limitations)

stm32f401 - 4-polysynth + additive/saw + monodelay

Initial stab at morphing wavetable osc
(note to self: here morph between H2/H3, triangular morph LFO @ 2Hz)

stm32f401 - 4-polysynth - wavetable morph

Created during 3-day ACT Festival workshop, demo of 2-track sequencer (no MIDI) w/ interactive scale-locked transpose control. Sine oscillators only for more minimalism

Sign up for more workshops: http://workshop.thi.ng

stm32f401 - 2-track sequencer (sines only, ACT workshop)

Same as previous track, but applying another LFO to LFO used for wave table morphing. This secondary LFO is tuned to go upto 3520Hz (so not really LFO range anymore) to create ring modulation effect...

stm32f401 - wave table morph - ringmod (London workshop)

Finally implemented IIR filter code with separately adjustable cutoff, resonance and resonance damping (for extra ringing). Here testing with 4 different oscillators: square, saw, sin-exp & sin-pow

stm32f401 - filters (London workshop)

2 track seq (each w/ 2 saw osc), high pass filter. Live modulation via via Korg Nanokontrol2

stm32f401 - saw - highpass - nanokontrol

Demonstration of artificial bit saturation & overdrive (14bits, 12bits, 10bits, 8bits)

stm32f401 - synth - saturation & overdrive

Hardsaw => Hardfloor, a little homage to: https://www.youtube.com/watch?v=Un4CeV_l3pI

stm32f401 - synth - hardsaw (12bit saturation)

Testing new stack-based synth implementation. Each voice uses 15 operator nodes, in order: env, lfo1 (pitch), lfo2 (vol), osc1, osc2, sum, foldback, mult, LP filter, delay1, HP filter, delay2, delay3, madd, panning

stm32f7 - synth- foldback distortion

New Formant synthesis oscillator type + Lowpass Filter (w/ random cutoff) + interactive delay feedback control

stm32f7 - synth - formant synthesis

4 voices + 1 formant osc + high pass filter (w/ random cutoff) + simplex noise based automation of delay feedback 

stm32f7 - synth - formant synthesis (drones)

Same setup as previous drone, but different formants, faster sequence, also using highpass filter

stm32f7 - synth - formant synthesis (highpass seq)

Randomly generated formant osc coefficients for each note + foldback distortion + 300Hz HP (q @ 0.8) + manually controlled delay + keychanges. Sequence else completely generative.

stm32f7 - synth - formant funk

probabilistic sequencer + formant osc + sawsin subosc (w/ synced impulse freq mod) + initial aux bus implementation (still all mono)

stm32f7 synth - formant + subosc + aux

2 tracks (8 voices) of initial stab at Karplus-Strong (https://en.wikipedia.org/wiki/Karplus%E2%80%93Strong_string_synthesis) with randomized impulse length & filter coefficient + LFO-based stereo panning + delay. Second melody plays a 5th and has LPF linked to note to create more of a nylon string character

stm32f7 - synth - karplus-strong (2 track)

adding/testing some of the KS extensions described in http://static1.1.sqspcdn.com/static/f/1195073/15927045/1326030818550/Jaffe-Smith-Extensions-CMJ-1983.pdf (still not addressed tuning issue for higher notes)

stm32f7 - synth - karplus-strong ensemble

Experimental spiral oscillator (x 2, slightly detuned) + fixed LPF @ 11.8kHz. Oscillator takes y-value of 2d spiral equation to produce waveform (with PolyBLEP to smooth). No filter modulation. LFO is only used to modulate number of spiral turns/twists (0.5 - 3.5)

sin(lfo * phase) * phase / TWO_PI

stm32f7 - synth - spiral

Temporarily going back to basics (in terms of features): 4 variations of first 100% Forth based synth & semi-random sequence using barebones of the new audio DSL. More info: https://hackaday.io/project/9374-stm32f47-synth/log/31951-proper-project-name-and-100-forth-example

synstack - forth - seq variations

Another bunch of variations (using different LFO settings) of the test bass step sequencer. More info: https://hackaday.io/project/9374-stm32f4f7-synstack

synstack - forth - bass seq variations

With the current API about 100 lines of Synstack Forth:
3 osc, 3 lfo over 2 independent tracks

1) kick drum (using sine osc + impulse osc for lfo/fm), 40% chance per step
2) bass seq 2 sin osc each w/ pitch lfo & env modulation (lfo1 randomly switching freq using lookup table of 8 diff. freqs)

synstack - forth - 2track - probabilistic

Some dirty easter beats made w/ Ableton + fat bassline and other synths brought in (sampled) from STM32F7, courtesy of http://thi.ng/synstack

20160325 sketch (STM32F746 + Ableton)

Best enjoyed with headphones! Recorded live set in hotel after last minute tech issues during my lecture. Turned out the Korg nanoKontrol lost its configuration earlier - such a shame, was looking forward to hear it on big speakers! :)

Synth is running on a £35 STM32F746-DISCO board and also implements a 2-track 8-step sequencer w/ interactive controls for osc waveform, filter, env, delay, LFO and global transpose all via Korg nanoKontrol... Activated notes are randomly picked from a fixed scale (only once, not random at every invocation)

STM32F7 live recording (Resonate)

http://thi.ng/synstack demo running on ARM Cortex-M7 / STM32F746-DISCO, full source code http://github.com/thi-ng/ws-ldn-12 (ex07)

stm32f7 - synstack - 3 osc + fb + sdramdelay (WS-LDN-12)

Another workshop example (ex06), more info here: http://thi.ng/ws-ldn-12

forthcharlie

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