IK8YFW Giuseppe has used a cheap US$2 processor to create a DSP audio processing unit that works with any radio (including the µBITx).
The project was aimed at achieving an economic and simple DSP unit, based on the ARM Cortex STM32f103 processor module. Guiseppe implemented two narrow CW filters of about 300 and 700 hz and two SSB filters with a bandwidth of less than 2200 Hz and less than 3300 Hz. He also included a 6-level noise reduction algorithm. The project is a very cheap solution suitable for embedding in any and every QRP project. The project code can be found on Github. It is not perfect, as Guiseppe is still experimenting with the code. The project can be found here:
Some test here: