videos in AudioSet
A list of about a million ten-second YouTube clips, each labelled with the sounds in it, that Google published in 2017. Labs use it to train and test general audio and music models.
Including AVR MIDI NES-style chiptune synthesizer waveform test, Obscura, an Arduino-compatible MIDI 8-bit Chiptune Synthesizer, Arcano MIDI NES Chiptune Synth II - an AVR, Nintendo-style synthesizer