Portable DIY Teensy Synth
Chowdah 
Programming
Code for the synth is found here on GitHub. Load this onto your Teensy 4.1, as outlined in this Getting Started with the Teensy article. Additionally, transfer clips found in the samples directory onto a Micro-SD card for playback, and insert the card into the Audio Shield. If everything was done properly, you now have a working arcade synth — ready for entertainment and music creation in any situation!
If you want to change the samples around, save new clips at a 44.1 kHz sample rate and 16 bits per sample with the exact names as are on the originals. Mono was appropriate for this application, though the Teensy has no problem handling stereo signals (and beyond) when needed. I used Audacity to transform clips into the correct format, which is a great (and free) tool for this sort of job.