After trying many different libraries I finally settled on https://github.com/shorepine/amy

It just works, it is simple to use, and has a great variety of patches (I am using the Yamaha DX7 Accordion in the video) and is event-driven, so it is a breeze to develop for.

Here is the repo https://github.com/campidelli/arduino-accordion, you can check the other branches where I have tested:

• https://github.com/sensorium/Mozzi
• https://github.com/marcel-licence/ML_SynthTools
• https://github.com/pschatzmann/arduino-audio-tools
• https://github.com/earlephilhower/ESP8266Audio/tree/master/src/libtinysoundfont

They all have pros and cons, but I found Amy the easiest to work with.

Here is the video with the accordion sound!

Next step: the 74HC165 chips got here, I will add them to the circuit and start looking at the melodica keyboard.