Teensy forum user kxmx_kaugummi has made a multi-channel audio codec breakout board for their modular synth set up using the Teensy and a Cirrus Logic CS42448.
An audio codec is a device that translates an analog audio signal into digital signals and turns digital back into analog. This gives us both an analog-to-digital converter (ADC) and digital-to-analog converter (DAC) that run off the same clock signal. The Cirrus Logic CS42448 is a popular 6 input, 8 output audio codec supported by the Teensy Audio library.
Teensy forum user kxmx_kaugummi used the Cirrus Logic CS42448 with a Teensy, breaking out the 6 input and 8 output differential audio signal pairs of the CS42448 and routing the digital signaling (TDM) and control (I2C) to the Teensy. This gives lots of audio channel in and out of Teensy, in a smaller, more modular form factor than other CS42448 boards.
You can find the schematic and bill of materials for both the Teensy 3.5/6 and the Teensy 4.0 over on kxmx_kaugummi’s EasyEDA page.