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https://github.com/thi-ng/synstack

Modular soft synth & Forth based VM for audio DSL experiments aimed at embedded devices
https://github.com/thi-ng/synstack

audio c11 dsp forth portaudio stm32 synth vm

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Modular soft synth & Forth based VM for audio DSL experiments aimed at embedded devices

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README 

        
* thi.ng/synstack



Softsynth engine for tiny & not-so-tiny devices...



** Contents                                                        :toc_3_gh:

 - [[#thingsynstack][thi.ng/synstack]]

     - [[#overview][Overview]]

         - [[#demos][Demos]]

         - [[#node-dag-synth-engine][Node DAG synth engine]]

         - [[#forth-like-vm-based-synth][Forth-like VM based synth]]

     - [[#build-instructions][Build instructions]]

     - [[#examples][Examples]]

         - [[#interactive-examples][Interactive examples]]

         - [[#forth-repl][Forth REPL]]

     - [[#contributors][Contributors]]

     - [[#license][License]]



** Overview



[[./assets/thing-synstack.jpg]]



*** Demos



- [[http://soundcloud.com/forthcharlie/sets/stm32f4][Demo set with 40+ tracks on Soundcloud]]

- [[https://www.youtube.com/watch?v=41FKE3PYjnE][STM32F746 MIDI synth (live performance, 2016-01-31, Youtube)]]

- [[https://www.youtube.com/watch?v=3lL-ZxyrHiE][STM32F746 synth (live recording, 2016-01-28, Youtube)]]



Please visit [[https://hackaday.io/project/9374-stm32f4f7-synstack][project log @ Hackaday]]

for interim updates, including a PDF with more project details. Thanks!



This repo currently contains two different experimental & easily

extensible implementations of a modular soft synth engine, both

written in portable C11 and originally developed for the STM32F4/F7

platform. However, for practical reasons (repo size, easier debugging

and dev workflow), both versions currently included here were prepared

without STM specifics, have been tested on OSX & Linux and [[#examples][include

several examples]]. Demo file size after stripping is between ~22-40KB

(for 32bit, bit larger for 64bit).



The sub-directories contain:



*** Node DAG synth engine



- =src= - an earlier (2nd or 3rd) iteration of the CTSS synth engine,

  using block based operators & node DAG (directed acyclic graph):

  - 10 oscillator types (incl. formant & karplus-strong, polyBlep antialiasing)

  - flexibile LFO setup (global LFO & arbitrary per voice)

  - filters (biquad, IIR LP/HP/BP, formant)

  - ADSR

  - foldback distortion

  - buffer ops (sum, product, product sum)

  - mono / stereo delay lines w/ feedback

  - mono / stereo mixdowns (int16 & float)

- =examples= - examples for this version of the synth (using

  Portaudio, see below)



*** Forth-like VM based synth



(not embracing ANS Forth standard here):



The supplied Forth-like VM & core vocab is general purpose, is configurable

(e.g. support for floating point & automatic inlining) and can also be used

independently, outside this project. In fact, the synth DSL related aspects

are implemented as add-ons and can easily be removed.



- =src_vm= - actual stack VM, interpreter & compiler w/ basic

  inlining, REPL, core Forth dictionary & basic synth operators (still

  need to port more from =src=)

- =examples_vm= - Forth examples (see below)



** Build instructions



Requirements:



- [[https://premake.github.io/][Premake5]]

- [[http://www.gnu.org/software/make/][GNU Make]]

- GCC / Clang (w/ C11 support)



The library itself has no 3rd party dependencies. Some of the examples

however use these additional libraries:



- [[https://github.com/thi-ng/ct-head][ct-head]] (included as submodule)

- [[http://portaudio.com][Portaudio]] (on OSX can be installed via =brew=)

- libncurses (part of OSX & Linux)



#+BEGIN_SRC shell

git clone --recursive https://github.com/thi-ng/synstack



cd synstack



premake5 gmake



make -f ctss_old.make config=release_sse



make -f ctss_vm.make config=release_sse

#+END_SRC



** Examples

*** Interactive examples



Use the above build instructions to build all components & examples.

Almost all demos in =examples= implement a simple randomized sequence

playback (some with multiple voices) and are using the same

interactive controls:



| *Key* | *Description*      |

|-------+--------------------|

| =-=   | dec delay feedback |

| =+=   | inc delay feedback |

| =[=   | pitch -2 semitones |

| =]=   | pitch +2 semitones |

| =;=   | pitch -12          |

| '     | pitch +12          |

| =q=   | quit               |



The two exceptions are:



- [[./examples/synth_keys.c][synth_keys]] - play a new note with each keypress (fixed sequence, =q= to quit)

- [[./examples/synth_render.c][synth_render]] - non-interactive demo, creates /sound.wav file (runtime ~20secs)



#+BEGIN_SRC shell

  # if you followed above build instructions, the demos can be launched like:

  bin/release/synth_spiral

#+END_SRC



*** Forth REPL



Use the command below to launch the VM with input file. Also see

[[./examples_vm/bass-seq.fs][example source code]]. In this mode the VM goes straight into playback

mode and is non-interactive (hit =Return= to quit).



#+BEGIN_SRC shell

  bin/release/repl examples_vm/bass-seq.fs

#+END_SRC



To launch the Forth REPL in interactive mode:



#+BEGIN_SRC shell

  rlwrap bin/release/repl

#+END_SRC



There'll be alot of output initially (inlining statistics by the Forth

compiler), but no visible input prompt. Try some of the following (hit

return after each line, comment lines are prefixed with '\\')...



#+BEGIN_SRC forth

  \ evaluate expression

  \ forth uses RPN, the '.' word pops & prints the top stack item

  \ forth is a hybrid between interpreted & compiled execution

  1 2 + .

  \ 3



  \ define new word (here to calculate a * b + c)

  \ the (...) form is a stack effect comment:

  \ here it means the word consumes 3 items from the stack

  \ and after execution a new item (result) is on the stack

  : madd ( a b c -- x ) -rot * + ;

  3 5 10 madd .

  \ 25



  \ the VM differentiates between int & float based math

  \ float ops are prefixed with 'f'

  : maddf -rot f* f+ ;

  3.f 5.f 10.f maddf .f

  \ 25.0



  \ store values in "variables" (labelled addresses)

  23 var> foo !

  \ get var value

  foo @ .

  \ 23



  \ by default the VM includes the dictionary of synth related words

  \ (defined in /src_vm/synth_dict & various C files in /src_vm)

  \ for example note names map to their frequency

  A4 .f

  \ 440.000000



  \ convert frequency to ratio of sample rate

  A4 hz .f

  \ 0.062689



  \ allocate memory for note/chord lookup table

  C3 E3 G3 A3 4 dup allot dup var> chord ! swap ds>dict!



  \ define word to randomly choose note from chord

  : rand-chord-note ( -- freq ) 0 4 rand chord @ + @ ;



  \ call several times

  rand-chord-note .f

  rand-chord-note .f

  rand-chord-note .f



  \ disassemble word

  see> rand-chord-note

  \ 0x000004da :0x0301a88a docolon

  \ 0x000004db :0x00000004 lit 0x00000000 

  \ 0x000004dd :0x00000004 lit 0x00000004 

  \ 0x000004df :0x00000081 rand

  \ 0x000004e0 :0x00000004 lit 0x000004d3 

  \ 0x000004e2 :0x0000002a @

  \ 0x000004e3 :0x0000004b + 0x0000002a (0x0000050e )

  \ 0x000004e5 :0x00000002 ret



  \ display data stack contents with .s

  1 2 3 .s



  \ display VM stats

  .vm



  \ display list & addresses of all words currently defined

  \ also see /src_vm/core_dict.h how some control structures

  \ are defined in forth itself

  .words



  \ display hexdump of VM memory

  .mem

#+END_SRC



** Contributors



| *Name*          | *Role*                          | *Website* |

| [[mailto:[email protected]][Karsten Schmidt]] | initiator & principal developer | [[http://thi.ng][thi.ng]]    |



** License



This project is open source and licensed under the [[http://www.apache.org/licenses/LICENSE-2.0][Apache Software License 2.0]].