PIC-based fraktal synth

hanley · Joined: May 24, 2006 Posts: 27 Location: London

This sounds great! Must dust off my fraktal synth

hanley · Joined: May 24, 2006 Posts: 27 Location: London

okvern · Posted: Tue Oct 12, 2010 10:17 pm Post subject:

Hi hanley,

Hm. I'll have to dig it up. It's been awhile! Just off the top of my head: it's pretty easy to throw together MIDI sequencers if you use this MIDI library:

http://www.arduino.cc/playground/Main/MIDILibrary

...and use the scheduler library by Alexander Brevig, aka AlphaBeta:

http://www.arduino.cc/playground/Code/Scheduler

If you use Scheduler and respond to MIDI note on messages in an interrupt, timing can be quite good. I have a hacked version of the Scheduler library based on MIDI clock pulses (rather than time) that also lets me schedule MIDI events (note values, velocity, etc.). In between clock pulses, the sequencer throws upcoming MIDI events into the schedule; when the clock pulse fires an interrupt, the sequencer sends the events that are currently scheduled to run at that time and then returns to getting ready for the next clock pulse. The sequencer takes a MIDI clock via RX, and sends MIDI messages via TX. The program in the video is just playing a test sequence I put together.

It's been about a year, though, so it'll take some digging!

Thanks,

Ole

okvern · Posted: Tue Oct 12, 2010 10:20 pm Post subject:

I guess I should have said: it *feels* like it's been about a year.... Smile

I've gotten distracted with some other stuff that I'll unveil pretty soon.

Thanks,

Ole

Blue Hell

monokinetic · Joined: Aug 01, 2006 Posts: 100 Location: prague

Yerpa58,
I finally managed to make some time to upload the new .hex, mmmmm I already enjoyed some nice metallic drone patches. Great work man!

I wonder if we should collect all of the info togetehr to create a manual i.e. which display symbol is which patch and what the pots do for each.

Anyone think that would be useful?

David

State Machine · Posted: Fri Nov 26, 2010 6:52 am Post subject:

yerpa58 · Posted: Tue Nov 30, 2010 11:35 am Post subject:

I have been meaning to do a brief instruction manual. I would also like to do a new board layout using one of the faster PIC chips so that I could add an LED next to each pot to indicate when that pot is active. Not all of the algorithms use all of the pots, so it can be confusing to use the fraktal synth.

Still, I was surprised how good it sounded through a bigger amplifier & speaker, there is a lot of good low-end sound that is completely lost through the little on-board speaker and amp.

Also notice that the new drone algorithm reads the freq pots continuously, but does not change the pitch until the crossfade volume goes to zero. That way, the new tones fade in smoothly when the old tone fades out.

yerpa58 · Posted: Wed Dec 29, 2010 8:57 am Post subject:

Here is a cheatsheet for the fractal synth settings, I hope this helps.

fraktal_synth_chart.pdf

Description:

preliminary - let me know if you see any errors

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fraktal_synth_chart.pdf

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State Machine · Posted: Wed Dec 29, 2010 9:05 am Post subject:

oootini · Joined: Oct 15, 2007 Posts: 80 Location: ireland

a pcb of this would be great! 2+ voices would be fantastic.

this was such a great starter project for me. i bet if you got the documentation put together nicely and a pcb you'd get a lot of interest. i still haven't got round to trying out the new firmware though, looks great yerpa...

cloudscapes · Joined: Feb 09, 2004 Posts: 100 Location: Montreal

Has a block diagram of this been posted anywhere? I thought I'd try reinterpreting it to AVR.

I really suck at math so I might not be able the handle the fractal parts. Maybe I'll do the brute-force approach. Random numbers with linear interpolation, or wavetables.

State Machine · Posted: Tue Jan 04, 2011 8:51 pm Post subject:

yerpa58 · Posted: Tue Jan 04, 2011 9:09 pm Post subject:

Will you get two voices by using two PICs? That might call for a new patch to do a beatbox rhythm thing. These PICs are really a lo-fi blast, and having the multiply instruction makes them pretty versatile.

As far as math, there isn't much. The "fraktal" patches are shift registers with logic and feedback applied in a simple way that the PIC can do quickly.

I'm posting the code and cheatsheet to the web at

www.yerpa58.com/fs2.htm

but give me till tomorrow to get the last page done.

Cheers!

State Machine · Posted: Wed Jan 05, 2011 8:17 am Post subject:

yerpa58 · Posted: Wed Jan 05, 2011 9:00 am Post subject:

State Machine, that sounds like a nice board. I wish I had included an ICSP header, it sure would be easier than popping chips in and out.

A lo-fi beat box with sync in/out would be a cool patch addition. Most algorithms on the fraktal synth use the Speed parameter, this could also generate a Sync Out pulse which would be useful with presets like the fraktals and the sequencer. For some other presets, maybe sync could be ignored. I'm just tossing ideas out, the more time I spend thinking about it, the faster the code comes together.

yerpa58 · Posted: Wed Jan 05, 2011 9:01 am Post subject:

Also, the latest code including 2ToneDrone, is at:

http://www.yerpa58.com/fs9.htm

State Machine · Posted: Wed Jan 05, 2011 9:39 am Post subject:

State Machine · Posted: Tue Mar 01, 2011 1:44 pm Post subject:

I have the duel fraktal synthesizer on the breadboard and I am a bit mystified as to how to get the "plucked string" patch to work. It seems not to make any sound at all no matter what is done with any of the potentiometers. I do have the latest code loaded (it added the TT Drone) and both MCU's behave the same so there are no errors in the circuit.

Any advice ?

Bill

yerpa58 · Posted: Tue Mar 01, 2011 2:14 pm Post subject:

Bill,

I think one of the four control switches might have to be in a certain position for the strings to play. I'm not sure which switch it was, but I know it was not the vibrato switch.

I'm away from the shop right now but I may be able to swing by tonight and check it out for you.

State Machine · Posted: Tue Mar 01, 2011 2:33 pm Post subject:

JovianPyx · Posted: Tue Mar 01, 2011 2:37 pm Post subject:

Hello Fraktal folks,

I have 10 dsPICs here, but have not yet used them. I'm looking for a nice first project - I would love to hear some sound samples, I am assuming that the PIC generates the sound? - any chance that someone can post an MP3 with examples of the different patch settings?

I admit that I've no idea what a fraktal synth is, but I'd love to find out and if it fits in with my personal music needs, then I'd like to build one. I figure if it can be done in a PIC it ought to be possible in a dsPIC - no? The dsPICs I have come with in-chip stereo 16 bit DAC (100 kHz) and two UARTS, so sound output and MIDI input are very little additional circuitry.

yerpa58 · Posted: Tue Mar 01, 2011 2:55 pm Post subject:

JovianPyx,

There are all kinds of sound samples earlier in this thread. Yes, the PIC produces the sound directly using PWM through a simple RC filter. I've also been doing a lot of dsPIC programming lately and thought about porting the fraktal synth from the PIC 18F to the dsPIC. I wondered how it would sound with 16 bit words vs the 8-bit PIC. Probably more of a hi-fi sound, but that might wreck some of its appeal.

I'm very impressed with your FPGA projects - they sound great!

JovianPyx · Posted: Tue Mar 01, 2011 4:01 pm Post subject:

heh, I sorta like hifi, not sure why ... I went through the thread, but didn't see MP3 posted - is it links? OH MY, I didn't realize it was so many pages...

And I think you could provide a lo-fi option using a dsPIC just by writing zeroes to the lower 8 bits of the DAC... That could be configurable, in fact, select the number from 1 to 16!

Ok, I got sounds now, and I see there's some analog electronics including a filter. I believe I can do a digital state variable filter in a dsPIC and eliminate some of that. The dsPICs I have are dsPIC33FJ128GP802 with 128K program space.

And thank you yerpa58 for the nice comments about my "stuff". Smile

Interesting sounds, kinda synchy. I could use this.

monokinetic · Joined: Aug 01, 2006 Posts: 100 Location: prague

Aha well there has been some interesting discussion that I almost missed out on. Bill the 2 PIC board with ICSP sounds super. I thought I could mention that I recently had a lot of fun sending 0-5v control signals from some basic Lunetta type LFOs into the PIC synth. Maybe your board could have patch points for the pot ins to accommodate also sending in such CVs?

JovianPyx, I think Catweazle's original FTP had some fraktal synth example MP3s on it, but it seems to be down. I have sent him a mail to ask if it's OK to repost them. In the meantime, I could record some examples of Yerpa58s more recent additions if you like?

In the original discussion about the fraktal synth algorithm Catweazle posted this link:
http://www.instructables.com/id/Predictive*-digital-music-synthesizer-Pandora_s-B/

I think it would be very interesting to implement this type of algorithm with a higher sample rate on a dsPIC, it spits out some very interesting noises. I have been using my fraktal synth live quite a bit and having heard it through a few KW sound system it rocked!

I still plan to make an attempt to integrate Catweazle's synchronisation suggestions he gave me in this thread last year. One of my stumbling blocks has been that the code requires a paid C compiler. I wonder how hard it would be to port to the Microchip toolchain, or even SDCC. A more accessible toolchain might encourage more people to have a hack at the code...

Anyway, just my 2 (Euro) cents!