Small 'synth on a chip' to control via a PIC?

[Gurner]

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.

[Taylor]

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.

[Gurner]

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.

[cpm]

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.

[Gurner]

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.

[JFX09]

Get yourself  ''The VCO Chip Cookbook'' by Thomas Henry, ther's a whole section on the XR-2206

[potul]

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/

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

Regards,

Mateu

[Gurner]

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!)

[slacker]

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. The top 2 CD4007 gates replace R1 and R2.
A PWM signal into the frequency input would let you control it digitally.

[Gurner]

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. 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.

[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