Building a Simple DIY USB MIDI Controller using Teensy : Ask.Audio
Paul Stoffregen on Twitter: "Teensyduino 1.52 release today, with much more than just Teensy 4.1 support. OctoWS2811 on any pins, T4 USB Audio, Dual & Triple USB Serial, 6 & 8 channel
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Amazon.com: Audio Adaptor Board for Teensy 4.0 : Electronics