The Guitar Effects & DSP Box

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About Mark-Toys

 DSP Audio Processing Using  56000  DSP

This page presents a very complex project I had taken on around 1995 or so back when the DSP bug had hit me and I was taking many classes on DSP processing and so on.    The beauty of the FFT is 'pure' but lest I digress perhaps I should just discuss the project now ...   

A fully functional device was built from processor board design up that uses the Motorola 56000 DSP chip.  It was a one-board wirewrap board with audio circutis done point to point wiring.    The board sported a high speed A/D and analog fairly standard audio input circuits made using assorted OP-Amp tricks I had been versed in prior job experiences.  There was also a two line display that accepted simple serial input that I drove for human readability.   Lastly there was assorted chassis issues and fairly stock keyboard scanning algorythem which by the time of this project I had done that sort of thing many times over for assorted instruments in my prior engineering of many processor boards/embedded software instruments at HP in the 80s through 90s.

This project could do two things of note depending on the eproms I plugged in at any given time.    The first project I coded for it was an FFT analyzer that was able to take in audio and then output a sync pulse and an analog trace sutiable to run a normal analog scope.  This had a few tweekable parameters but was more or less a test for the circuits so I did not use this much after I had made it.

The second project of much greater software complexity was an audio processor geared towards the range of audio that a normal electric guitar puts out.    For this the system could do a chorus, reverb, delay and I fiddled a bit with assorted distortion and compression but lost interest in that after a while and shelved this project to move on to other things.   Here is a parameter entry screen for digital delay.

Digital Delay Input Screen
Digital Delay Input

I was doing a LOT of recording of songs and so on and one only has so much time to 'play'.  

The code for the projects were both fully assembly code where the bulk of the code for actual effects or FFT was found already coded so I pieced together these pieces and formed the OS for this assembly based processing system with high rate of interrupts and keyboard input with text display output.   

Inside Electronic Guts

Because the circuit board was all hand wired electronics of my own custom design it was very rich in digital design and in analog front-end high speed acquisition logic.   Below is the top of the circuit board and I assure you the bottom is a TON of point to point wires all in wirewrap for the most part escept the analog which was point to point for reasons of better performance.  The board to the right was one of my own HP embedded processor boards with a custom video overlay programable logic but the board is only used here as a genearal processor and display/keyboard interface.

The Mega-HandWired Circuit Board


This was a HUGE project and I hope you found this project interesting and motivating.