The DSP-59+ Audio Digital Signal Processor uses digital signal processing technology to provide optimum filters for random
noise reduction, heterodyne elimination, highpass filtering, lowpass filtering, and bandpass filtering.
Digital Signal Processing (DSP) technology provides superior performance in reducing QRM and QRN.

Specification/Description: https://www.timewave.com/products/Datasheets/59pdata.html

Manual: http://old.timewave.com/support/Manuals/DSP59POM.pdf