The first digital pitch shifter created originally for speech pathology. To adjust pitch speech in real time without affecting the time. Using an 8bit processor, it is a dirtier pitch shift But has its own character. Not much info on this - but the following model - 27 - has been used widely in music production. These are pretty rare and I haven’t found a functioning one for sale. I had this serviced and had custom made chips for those that are obsolete.