PIC hybrid synthesizer

Design Concepts
1

Hi!

It’s saturday, I’d nothing to do, so I brought some ideas to paper:

This is my concept of a modular hybrid synthesizer using 3 PIC, EPROM and some cheap logic and analog components. I think that works fine, and the PICs have much time to calculate their parts.

How it should work:

Each µC-Board listens to the same midiconnection, and each of them use only the data it needs, eg board 1 only takes note-on and note-off events. Each board calculates independently. The PIC on board 2 uses the timer to read the input and to output the results.

Board 3 & AOUT are the things TK made already.

The clock generator is basicaly a downcounter with 2 latches using a high frequency crystal to work. There is a similar board here:

http://www.cgs.synth.net/modules/cgs20_dco.html

The wavetable is an EPROM driven by a counter, similar to this:

http://www.cgs.synth.net/modules/wavetable.html

VCF … I don’t know, there are a lot of schematics…

DAC is simple IC, eg DAC0830, DAC0832…

So, what do you professionals  ;D think about it? Does it work, or am I wrong?

It is a modular hybrid wavetable synthesizer, you could add additional digital parts between board 2 and the DAC, you could also add analog parts between DAC and VCF… I guess it would be realy cool, if it works that way  ;D

THX

Maik

2

Hi Maik,

it should work, it’s a nice modular solution!

Best Regards, Thorsten.

3

Hi,

If I may suggest:

Implement a 8 bit wavetable in the ROM internal to PIC#1 (using “retlw” instructions) and output an analog waveform using PIC#1’s CCP1 and CCP2 PWM output. This allows for 2 channels.

Implement the amplitude env+mod with a simple VCA with control voltage coming from an Aout Channel associated with PIC#3.

This removes the need for PIC#2 and external ROM and DAC. You could duplicate PIC#1 for more voices.

cheers

4

The idea of using pwm as analog output is good, but I guess that there are a lot of errors in the signal, because the caps may be to slow. I don’t know, I’d never tried it.

I’m working on my selfmade testboards with AVR at the moment. I think it is possible, to generate waveforms with 1 AVR, and without an external EEPROM. When I use the slowest prescale timer, I can get a sampling rate around 16kHz and have 1024 cpu cycles to generate each sample. When I use precalculated waves from the internal EPROM or SRAM, I guess that works.

I’ve seen PICs with 40MHz. When an AVR isn’t enough, then these PICs may be the solution.

My biggest problem is the DAC. I’ve around 20 DACs flying arround, but I’d never get one to do what it should do  ;D

5

Hi,

For some inspiration, check the avrsynth: http://www.jarek.synth.net/ and ATMEGA16 version: http://www.elby-designs.com/avrsynth/avrsyn-about.htm

These are simple 2osc synths with LFO, LP-filter and EG..

It would be nice to see a polyfonic wavetable synth..

Bye, Moebius :smiley:

6

Hi ,

the PWM frequency of a 20MHz PIC with 8bit resolution is very high >64kHz if my memory is right, (the datasheet  will confirm this) so the RC can be made very short.

cheers