Forum user gi1mic has released a DIY DSP audio project for radio hams.  It takes advantage of the processing power of the Teensy and implements finite impulse response (FIR) filters that are configurable in software and default to an impressive 200 taps.

For this project a Teensy 3.2 was added to a Yaesu FT-817 transceiver and is powered from the FT817.

Some of the other features include:

• Act as multiple DSP filters based on hi pass, lo pass, band pass or band stop (filter points can be defined in Hz within the code)
• It uses voice messages to describe which filter has been selected
• It is a USB to CAT interface
• It emulates a USB sound card for receiving rig audio on a computer
• Performs Morse to voice decode and Morse to USB serial decode
• It can speak the radio config to assist the visually impaired (FT817 only)

More details about the project as well as the open source code can be found here.