Just wondering if anyone could give me a lead or two wrt a good sound generating chip that I could control via a PIC? (ideally very small as I'm pushed for space)
It's very early stages, but I'm dabbling with guitar pitch detection & it'd be cool to have a sound generating chip on the same cct as the PIC. How are most synth chips controlled digitally (Midi? some bespoke protocol etc)
many thanks.
I think the way to do this would be to use something like the XR2206 or similar function generator IC. You can then control this with a digital pot, or apparently cloudscapes worked out a way to do voltage control:
http://electro-music.com/forum/viewtopic.php?t=39273
Might be worth bumping that thread of his to see if he has any other thoughts. He also comes by here sometimes, so maybe he'll see this.
That's exactly along the lines of what I was after - just this minute ordered one ....I'll be be in 'digital/CV controlled frequency' heaven tomorrow!
many thanks.
those signal generators usually put out a simple waveform (sqare, sin, triangle, etc), not a complex "synth" sound.
you may try generating the pulse directly from a pwm output in your pic if its powerful enough. Or a second dedicated PIC to generate the waveforms, which would be controlled by your main PIC using some signals.
A DIL8 PIC is even smaller than those F.gen ics.
I'm actually going for a two pronged approcach.
having the PIC (which is detecting the pitch in the first place), generate a simple waveform by waz of arrays (eg an array filled with data to recreate a sine etc)
but also will have a dabble with the function generator chip.
Ultimately I'd like to interface with a synth chip (polyphony, more complex waveform - suitable contender idea warmly accepted), but like I say this is early days & just getting a sound generated from the PIC derived pitch detection is my first target.
Get yourself ''The VCO Chip Cookbook'' by Thomas Henry, ther's a whole section on the XR-2206
This is something I've had in mind for a long time, waiting for a free slot in my schedule. Two possible approaches you could take:
1-Create a simple square signal from the PIC, and use analog circuit to "shape" it, filter it and so on (or a couple of them and mix them). Something like this guy is doing with the picsynth:
http://picsynth.000space.com/ (http://picsynth.000space.com/)
2-Use the PIC PWM to create the wave (low quality 8 bit)..., take a look a this synth only using PIC.
http://www.reprolabs.com/fraktal_synth_1.htm (http://www.reprolabs.com/fraktal_synth_1.htm)
Regards,
Mateu
Quote from: JFX09 on September 02, 2010, 10:28:56 AM
Get yourself ''The VCO Chip Cookbook'' by Thomas Henry, ther's a whole section on the XR-2206
Thanks I'll try to source it.
Any leaders for VCFs under digital control? (preferably using digital pot)
I've just referenced this one...
http://www.diystompboxes.com/smfforum/index.php?topic=52472.0
but it's not clicking what the equivalent circuit is (the schematic auther says he's using the CD4007 as two variable resistors - but I can't visualize what the overall picture is wrt the filter aspect - a block diagram of an 'equivalent circuit' would be nice to show what's being achieved!)
Ignoring the resonance part that filter is a Sallen Key lowpass filter, like the lowpass example here http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology (http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology). The top 2 CD4007 gates replace R1 and R2.
A PWM signal into the frequency input would let you control it digitally.
Quote from: slacker on September 02, 2010, 12:27:06 PM
Ignoring the resonance part that filter is a Sallen Key lowpass filter, like the lowpass example here http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology (http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology). The top 2 CD4007 gates replace R1 and R2.
A PWM signal into the frequency input would let you control it digitally.
Thanks ....that's exactly the kind of explanation I was after (I'd actually looked at wikipedia prior to asking, but couldn't correlate what was replacing what with that cd4007 circuit!), I guess I could simply replace those resistors with digital pots
Cheers,
Gurner.
My XR2206 arrived, but I'm not sure it's going to give the granualarity of control I need (no worries, it'll have a use somewehere!)
I've just ordered a DDS chip (bloody expensive @£14 ....$20), but from a nerdy perspective it's spec has me aroused...
http://www.analog.com/static/imported-files/data_sheets/AD9835.pdf