Random Timbre Synthesizer

JovianPyx

I've mostly completed a new FPGA MIDI synth project: A Random Timbre Monosynth.

Here is what that means for this synth:

Random waveshapes are generated using a 2 wavetable structure.

While one wavetable plays, the other is filled with a new waveform.

At MIDI clock (or a divide down of it) the synth will respond by generating a new random waveform in the "non playing" wavetable.

Variable time crossfade effect is implemented.

Crossfade time can be as slow as several seconds down to 1 millisecond.

The design also includes a lowpass filter to help limit buzziness if that is not desired. There are other controls that add or subtract from buzziness.

The system used was a Spartan-3E Starter Kit.

The synth also responds to MIDI note number and velocity, but that is not demonstrated in the samples. Portamento is implemented. Sample rate is 100 kHz with a 12 bit DAC.

Some example sound clips are below...

rts_rythmic_1ms.mp3

Description:

Random Timbre Synth Sample: Fast crossfade time with a rythmic change in timbre

Filesize:

337.99 KB

Duration:

0:22

Viewed:

2240 Time(s)

rts_slow_xfade.mp3

Description:

Random Timbre Synth Sample: Slow crossfade time with a rythmic change in timbre

Filesize:

656.35 KB

Duration:

0:42

Viewed:

2179 Time(s)

JLS · Posted: Wed Aug 17, 2011 6:40 am Post subject:

Nice sound example and nice synth idea - thanks

P.S. is possible post source code ?

THANKS

JovianPyx · Posted: Wed Aug 17, 2011 2:47 pm Post subject:

I will make the source available - when I get it finished. Right now, the synth itself works. I found I had 14 K of 18 bit wide block RAM left over, so I'm writing a delay effect into the design. It will go up to 143.36 mSec of delay (100 kHz sample rate), which will be looped. The output will be a wet/dry pan. pretty standard basic stuff, but it sounds nice and the RAM is just sitting there.

It needs a divider for the MIDI clock, right now it switches waveforms on every F8. That's easy, but I have to do it. And there's more testing to do, but I think the heavy lifting is finally over. The state machine has about 80 states in it, so it was "interesting" to debug.

Anyway, when I get that all working, I'll post a link to the source.

JLS · Posted: Thu Aug 18, 2011 2:06 am Post subject:

Thanks info and great work Smile

JovianPyx · Posted: Thu Aug 18, 2011 3:59 pm Post subject:

I got delay and the MIDI clock divider working, the sample contains some notes using a MIDI clock source from the sequencer playing the notes.

rts_sample_with_delay.mp3

Description:

Random Timbre Synth sequence with delay effect

Filesize:

251.86 KB

Duration:

0:16

Viewed:

2295 Time(s)

rts_sample_with_delay_2.mp3

Description:

Another sample, this one has a approx 120 mSec crossover time, same sequence. MIDI clock was divided more too.

Filesize:

235.54 KB

Duration:

0:15

Viewed:

2253 Time(s)

JLS · Posted: Fri Aug 19, 2011 2:01 am Post subject:

Nice sound example delay is very usefull !

Thanks

P.S. modulation delay will be great Smile

PHOBoS · Posted: Fri Aug 19, 2011 3:56 am Post subject:

sounds great scott!! Very Happy

JovianPyx · Posted: Fri Aug 19, 2011 1:23 pm Post subject:

I don't know why I didn't do it in the first place, but I added response to "MIDI start" (0xFA) to synchronize the synth to the sequencer driving it. The MIDI start message resets the MIDI clock divider counter to zero. In the short sample below, you can clearly hear that the waveform changes are synched to the beat. The sequencer was run at 100 BPM. Except for the last note, all the notes are half notes and 4/4 time. The synth's MIDI clock divider was set to 6.

rts_sample_rythmic_using_MIDI_start.mp3

Description:

Sample demonstrates synth's response to MIDI start message.

Filesize:

185.33 KB

Duration:

0:12

Viewed:

2145 Time(s)

JovianPyx · Posted: Fri Aug 19, 2011 5:44 pm Post subject:

This is a one minute drone I did.

rts_short_drone.mp3

Description:

A one minute drone.

Filesize:

1.02 MB

Duration:

1:07

Viewed:

2314 Time(s)

JovianPyx · Posted: Sat Aug 20, 2011 1:21 pm Post subject:

Source code.

The zip contains the Verilog source code for a Spartan-3E Starter Kit and VB.NET source code for the patch editor. Once expanded, you'll see a directory under "pub" called "Patch_Editor". There you will find the VB.NET source code for the patch editor. It works at least in Visual Studio 2008 VB.NET Express Edition (free). A cable is required to connect the DCE port of the FPGA board to the PC's COM port.

NOTE: The patch editor is a work in progress and was produced by modifying another similar program. The LOAD and SAVE buttons do not work. I believe there is no help file as well, so the Help button may give an error page. The portamento screen values are nonsense, but the slider does what it's supposed to do. Clicking the green SEND button will send the current patch to the synth. Make sure not to send patch data via the COM port while sending MIDI data through the MIDI port.

Source is here:

http://jovianpyx.dyndns.org:8080/public/FPGA_synth/Random_Timbre_Synth_ver_n_Source.zip

BobTheDog · Posted: Sun Aug 21, 2011 2:55 pm Post subject:

Hi Scott,

Those Spartan-3E Starter Kits look good value now, do you get all software required to program them with the kit? Is the software crippled in any way?

Cheers

Andy

JovianPyx · Posted: Sun Aug 21, 2011 3:44 pm Post subject:

I use the WebPACK ISE which is free. I am told that the pay-for-it version can get a few more percent of slice usage out of a given FPGA. But I've not had problems with "hitting the wall" that way. All of my synth projects were "compiled" with the free WebPACK ISE. The software is a big download. You have to register to get it. Also the embedded soft microcontroller I use is free as well - PicoBlaze. It's a 25 MIPS 8 bit RISC. The only cash I have invested in this is for the boards themselves. I had to build a tiny electrical interface to go from DAC to "audio out" and also a MIDI receiver. Those schematics are in the docs subdirectory of this project.

I actually like the DAC on the Starter Kit, it goes to 1.0 MHz sample rate. It's only 12 bits, but it actually sounds quite nice IMO, especially driven at high sample rates. The Starter Kit also has DDR DRAM which I've not yet used, but I must. Some 64 megabytes I think. ADCs too, but I've not used those either. 12 bit I think.

BobTheDog · Posted: Sun Aug 21, 2011 10:45 pm Post subject:

Hi Scott,

Thanks for the info, I will download your project and have a look.

Cheers

Andy

JLS · Posted: Tue Aug 23, 2011 11:45 pm Post subject:

Many thanks source code Smile

This is great work !

THANKS

JovianPyx · Posted: Thu Nov 03, 2011 3:03 pm Post subject:

I've made an improvement to the Random Timbre Synth. I've included an interface to the DDR SDRAM on the Spartan-3E Starter Kit that I use to implement a looped delay effect a bit over 20 seconds long.

A "snapshot" of the soundscape while using the synth is in the attached .flac file.

It's called One Note Samba because I put a weight on the sustain pedal and hit a low C. Delay time setting was something between 1 and 2 seconds, feedback was over 90%.

Random_Timbre_Synth_Drone_with_Delay.flac

Description:

Random Timbre Synth - Drone with Delay

Filesize:

6.72 MB

Duration:

1:54

Viewed:

2017 Time(s)