How to implement a Standalone instrument?

[campidelli]

Hi Mr Licence, how are you?

I want to make a simple instrument using a synth on ESP32. I have tried many other libraries but I can't achieve what I want. I understand it is a simple scenario, where I have a matrix of keys, let's say a piano, and for each key, I want to generate a sound and send it to my I2S DAC. But it had to be polyphonic.

I had a look at https://github.com/MichaelPNolan/StandAloneSynth37key/tree/main/esp32_alone_synth but I found it too complex, so many files. As a Java programmer I tend to use OOP as it makes more sense to me, so my idea of this standalone instrument would be something like this:

#include <Arduino.h>
#include "I2SAudioOutput.h" // Subclass of AudioOutput, has methods to stream audio
#include "Keyboard.h"       // Contains the logic to read the matrix and trigger events when keys are pressed
#include "Synth.h"          // Generates sounds

#define I2S_PIN_BCK  26
#define I2S_PIN_WS   25
#define I2S_PIN_DATA 22

AudioOutput out;
Keyboard in;
Synth synth;

void noteOn(byte key) {
  byte note = key + 60; // let's say key 0 is C4
  synth.noteOn(note);
}

void noteOff(byte key) {
  byte note = key + 60; // let's say key 0 is C4
  synth.noteOff(note);
}

void setup() {
    Serial.begin(115200);

    out = new I2SAudioOutput(I2S_PIN_BCK, I2S_PIN_WS, I2S_PIN_DATA);

    in = new Keyboard();
    in.onKeyPress(noteOn);
    in.onKeyRelease(noteOff);

    synth = new Synth(out, "PIANO"); // assume that I can create presets that make my synth to sound like a piano
}

void loop() {
  in.scan();
  synth.play();
}

Is it possible? If not, what is the minimum I need to do to achieve this result with your library?

Many thanks!

[marcel-licence]

Hi,

the file count can be reduced and most stuff is now placed in the library. I used the static memory allocation and c interfaces to get a better overview over the memory usage during compilation.

If you take a look at https://github.com/marcel-licence/ml_epiano_example/blob/master/ml_epiano_example.ino you might find a reduced example. You could use this as a basis a removed additional features like MIDI_STREAM_PLAYER, MIDI_VIA_BLE etc. and compile it for only one platform.

config.h keeps all global defines and z_config.z is used for the MIDI lookup table. I tried to reduce the allocations during runtime.

Does this help?
Best regards,
Marcel

[campidelli]

Hello Marcel,

So, this is my attempt to make it work https://github.com/campidelli/arduino-accordion/tree/ml-synthtools

I have kept everything to the minimum, so no fancy controllers and effects. But it has some problems:

• It doesn't compile, the error is

.platformio/packages/toolchain-xtensa-esp32/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: cannot find -lML_SynthTools
collect2: error: ld returned 1 exit status
*** [.pio/build/esp32dev/firmware.elf] Error 1

As you can see I am aware of the issue #46 and tried to use the script approach. I can confirm all the .a files have been renamed to have the prefix lib added to them.

I could use the PlatformIO branch but since I am using a Unix OS (MacOS), you would need to update this file (https://github.com/marcel-licence/ML_SynthTools/blob/platformIO/src/ml_inline.h#L43) to replace the back slash with forward slash

I also don't know if I need to keep the following code in the main.cpp file, because there are to Audio_Output in the main loop, one stereo and one mono.

    int32_t mono[SAMPLE_BUFFER_SIZE];
    Organ_Process_Buf(mono, SAMPLE_BUFFER_SIZE);
    Audio_OutputMono(mono);

Thanks, please let me know if I am on the right path.

[marcel-licence]

I've checked your project.
The python script adds on each try a lib to the library name ending up in liblibliblibliblibML_SynthTools.a

In main.cpp following is missing:

#define ML_SYNTH_INLINE_DEFINITION
#include <ml_inline.h>
#undef ML_SYNTH_INLINE_DEFINITION

In platformio.ini following should be used:

build_flags = 
  -D ESP32
	-L $BUILD_DIR\\..\\..\\libdeps\\$BOARD/ML_SynthTools/src/esp32/

I was hoping to find a variable libe $LIBDEPS_DIR or similar. Please let me know if you can find something to get a more generic config.

It is the right path =)

[marcel-licence]

I've created this now: https://github.com/marcel-licence/ML_SynthTools/blob/main/extras/platformIO_integration.md

[campidelli]

Amazing! We are making progress. The code now compiles and makes noise, but I still don't have polyphony, what tweaks do you suggest?

Here is the video of the demo:
https://www.youtube.com/watch?v=sMeF-W0hdi0

Cheers!

[marcel-licence]

Thank you very much for the demo.
You could try to attach a shift register to use more buttons or try to create an array. The diodes would allow to scan columns and check multiple rows.