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A Synthesizer Made of Only Filters
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JovianPyx



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PostPosted: Fri Dec 04, 2009 7:32 pm    Post subject: A Synthesizer Made of Only Filters
Subject description: A Synthesizer Made of Only Filters
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I have designed a synthesizer made of only filters. There are no oscillators in the design at all. It is also up to 32 voice polyphonic. I call it PolyDrum.

It has 32 state variable filters and 32 single pole IIR low pass filters and is implemented on a $39 FPGA development board.

The state variable filters form "resonators" and the single pole filters form exponentially decaying envelope generators. The envelope generators modulate the Fc input of the state variable filters to provide a variety of pitch modulation effects.

Each resonator is frequency, Q, EG and MIDI note number programmable. More than one resonator can be programmed to respond to a given note number - but all of the resonators responding to the same note number will begin their sound with a synchronized pulse

EDIT ADD 2009-12-05:
I should have added that the instrument is played (MIDI) by sending an impulse to any resonator that receives a match between the note played and the resonator's note number map (assignable). If the Q values are large enough, it will be very tonal with a long sustain.


PolyDrum_002.mp3
 Description:
A sample of the resonator synth. Each chunk of notes is done with the synth's parameters mostly the same, but one, envelope generator time, is increased for each chunk.

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 Filename:  PolyDrum_002.mp3
 Filesize:  3.09 MB
 Downloaded:  611 Time(s)


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Last edited by JovianPyx on Tue Jun 14, 2011 10:58 am; edited 1 time in total
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aerogramma



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PostPosted: Sun Dec 06, 2009 1:43 am    Post subject: Reply with quote  Mark this post and the followings unread

like its dirty sound... great!

Wink

aero
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PostPosted: Sun Dec 06, 2009 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Sounds great ScottG! Dirty and warm.

Smile
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JovianPyx



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PostPosted: Fri Dec 11, 2009 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's a piece of music made with the PolyDrum. I've set it up to be tonal again, but it is tuned an octave higher than the other clip I posted. It is also set to use each resonator as an individual drum (32 total drums).

I will be working on another piece of music that will demonstrate this instrument's more unusual sounds and behavior.


PolyDrum_004.mp3
 Description:
A piece of music played entirely on the PolyDrum synth. No effects were used to process this sound.

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 Filename:  PolyDrum_004.mp3
 Filesize:  2.63 MB
 Downloaded:  535 Time(s)


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Last edited by JovianPyx on Fri Dec 11, 2009 8:51 am; edited 1 time in total
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Blue Hell
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PostPosted: Fri Dec 11, 2009 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice organic sound!
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JovianPyx



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PostPosted: Fri Dec 11, 2009 8:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the nice comments. I was actually sort of surprised at the "earthy" sound I got, which inspired the piece.
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PostPosted: Fri Dec 11, 2009 9:03 am    Post subject: Reply with quote  Mark this post and the followings unread

great sound again scott and nice track too

I don't know enough about it but have you considered offering this as a DIY project?

aero
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JovianPyx



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PostPosted: Fri Dec 11, 2009 9:17 am    Post subject: A Synthesizer Made of Only Filters Reply with quote  Mark this post and the followings unread

DIY project - hmm. Yes and no. The biggest problem for that is that the FPGA doesn't come in a package that is easy to solder like TQFP. It's a BGA device (ball grid array) which requires some sort of oven to solder it to the board.

Because of the BGA issue - which is true for all Xilinx larger FPGAs - I have used premanufactured development boards.

But I'm not done... I may see if it's possible to use several smaller devices which are easy to solder - but that creates programming logistical problems that don't exist when the entire design fits into a single FPGA.

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kkissinger



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PostPosted: Fri Dec 11, 2009 9:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Intriuging. It really has a beautiful -- almost acoustic kind of sound.
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aerogramma



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PostPosted: Fri Dec 11, 2009 10:46 am    Post subject: Re: A Synthesizer Made of Only Filters Reply with quote  Mark this post and the followings unread

ScottG wrote:
DIY project - hmm. Yes and no. The biggest problem for that is that the FPGA doesn't come in a package that is easy to solder like TQFP. It's a BGA device (ball grid array) which requires some sort of oven to solder it to the board.

Because of the BGA issue - which is true for all Xilinx larger FPGAs - I have used premanufactured development boards.

But I'm not done... I may see if it's possible to use several smaller devices which are easy to solder - but that creates programming logistical problems that don't exist when the entire design fits into a single FPGA.


I see, I really don't know enough about this world. But I would defintely consider getting one as a voice bank.

Look forward to hear your other samples
Very Happy
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PostPosted: Fri Dec 11, 2009 11:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Scott,

Nice work and concept. Very Happy The timbre of the music has such a mellow effect as one would expect from your implimentation. Very nice use of the FPGA in a musical application. BRAVO again ....

Bill
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JovianPyx



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PostPosted: Fri Dec 11, 2009 12:13 pm    Post subject: A Synthesizer Made of Only Filters
Subject description: A Synthesizer Made of Only Filters
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Wowee, thanks to all for the positive comments.

You know, when I dreamed this up, I really thought this was a hairbrained idea that would probably not work very well. And the first version didn't. The problem was that high Q filters like these need a rather wide arithmetic buss. My SVF design uses 35 bit signed values as input and output and the integrators are 70 bits wide because a multiplier is used and it's output it 70 bits signed. Since I had the realestate, I just left the RAMs at 70 bits to prevent loss of precision.

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cloudscapes



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PostPosted: Sun Dec 13, 2009 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

this sounds incredibly lush! thanks for sharing!
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hexagon5un



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PostPosted: Wed Feb 03, 2010 10:33 am    Post subject: Re: A Synthesizer Made of Only Filters
Subject description: A Synthesizer Made of Only Filters
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JovianPyx wrote:
... I call it PolyDrum.

It has 32 state variable filters and 32 single pole IIR filters and is implemented on a $39 FPGA development board.


It sounds great, and that sounds like a great design. Can I ask, what is the development board that you're using?

I'm using the Spartan 3E kit for stuff now, but at the price I can't really see soldering it into a permanent project. For $40, we're starting to get reasonable.

(Oh yeah, and do you have code up?)
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JovianPyx



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PostPosted: Wed Feb 03, 2010 11:18 am    Post subject: Reply with quote  Mark this post and the followings unread

This is the board:

http://avnetexpress.avnet.com/store/em/EMController/Development-Kits-and-Tools/Avnet-Electronics-Marketing/AES-SP3A-EVAL400-G/_/R-8007786/A-8007786/An-0?action=part&catalogId=500201&langId=-1&storeId=500201

But it's $49 now.

Also - I hope that I wrote that it has no DAC and no MIDI electronic interface. I had to add both of those. The DAC board (CS4344) cost about $25 and I built the MIDI input on a piece of stripboard.

This code would work on a Spartan-3E board (500K gate part). But would need some modification.

The code for this project is not up... Not sure when I will do that.

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PostPosted: Wed Feb 03, 2010 1:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Beautiful track! Reminded me of little droplets of water forming into ice crystals. Like a little soundtrack to an alternative world Very Happy

More!

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PostPosted: Wed Feb 03, 2010 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great music, Scott, I put it on the playlist for my shows.

Les
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JovianPyx



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PostPosted: Wed Feb 03, 2010 3:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, here's the source code.

What isn't included is the VB.NET source for the programming user interface. This synth allows you to control a whole lot of parameters, so I wrote a VB.NET GUI for it that communicates through the board's USB TTY bridge. If you're interested, contact me by PM and I'll send the current version - currently it's kind of a mess and I don't want to post it the way it is. But at least interested persons can look at the Verilog code for the synth internals and get an idea of what I did.

State variable filters enhance gain when Q is more than one. That is, the peak amplitude at exactly Fc will be higher than the rest of the spectrum. This is true of both analog and digital SVFs. Because of this, I designed in a amplitude windowing feature that prevents binary overflow (sounds horrible) while preserving as much amplitude as possible. This is a cautionary note - you have to deal with this when making patches so that you get the best amplitude without causing a nasty ear ripping sound.


ver_f.zip
 Description:
PolyDrum Verilog Source Code

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 Filename:  ver_f.zip
 Filesize:  449.19 KB
 Downloaded:  199 Time(s)


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JovianPyx



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PostPosted: Wed Feb 03, 2010 5:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
Great music, Scott, I put it on the playlist for my shows.

Les


Thank you Les!

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JovianPyx



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PostPosted: Wed Feb 03, 2010 5:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

v-un-v wrote:
Beautiful track! Reminded me of little droplets of water forming into ice crystals. Like a little soundtrack to an alternative world Very Happy

More!


And thank you too v-un-v!

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PostPosted: Fri Feb 05, 2010 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
Ok, here's the source code....

What isn't included is the VB.NET source for the programming user interface. ... But at least interested persons can look at the Verilog code for the synth internals and get an idea of what I did.


Thanks very much, Scott. I'm just starting out with FPGAs and with DSP in general (though I have a background in the math from 60 degrees off to the left -- I'm a time-series economist by day).

I'm sure I'll have fun taking apart your code. My first job is going to be playing around with filters (FIR, IIR, and your state-variables). It's going to be hard to keep me from adding some VGA code and going for the cheap audio-visuals, but I'll try to stay focused...

BTW, there's a handful of us here (HacDC, a hackerspace in Washington DC) who've been participating in an FPGA workshop. We're now all at the stage of being just-barely-dangerous with the Spartan3E starter kit, so the mini-projects are flowing. I think we've all used some of your code from FPGAsynth.

So thanks again for sharing. If I get anything cooler than "hello world" going, I'll post it up here.

Elliot.
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JovianPyx



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PostPosted: Fri Feb 05, 2010 11:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Elliot,

VGA - heh, I've wanted to mess with that, but I've been pre-occupied... I'd be very interested in seeing some VGA code added to a synth. I've got several VGA monitors in good working order that I'm not currently using, so it would be fun to see something happen while a synth is playing sounds.

Or a video synth...

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PostPosted: Fri Feb 05, 2010 8:01 pm    Post subject: You inspired me Reply with quote  Mark this post and the followings unread

I think the Polydrum concept is so cool that I decided to try the technique on my Aries synth.

http://electro-music.com/forum/post-282892.html

Well... it is a little different because the Aries is a mono-synth. Instead of a bank of tuned filters I just vary the cutoff frequency to get different notes.

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v-un-v
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PostPosted: Sat Feb 06, 2010 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
v-un-v wrote:
Beautiful track! Reminded me of little droplets of water forming into ice crystals. Like a little soundtrack to an alternative world Very Happy

More!


And thank you too v-un-v!


My pleasure Smile

If you've got a Nord Modular to hand.... try my "KlingKlang" noodle patch. This was also (almost) entirely made using the vocal filter within the modular. I've never heard the patch on a fully expanded machine, but it sounded great on the unexpanded modular. Think 'Zen garden with many chimes blowing softly in the warm breeze' Exclamation Very Happy

The simplicity of your piece, was its power. Very Happy

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DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
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JovianPyx



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PostPosted: Fri Apr 08, 2011 4:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've been reworking some of my designs, the PolyDrum is now expanded to 55 voices from 32. The hardware is capable of 64, but the state variable filters misbehave when Fc is a bit too high, so I restricted it to 55. The highest pitch 3 or so notes are kind of plinky, but they are tonal and in tune so still useful.

Perhaps more banging and swearing can bring it all the way up to 64. Part of the problem is Q enhancement which creates a higher effective Q as Fc increases. I've found that there is a nonlinear curve associated with what the Q should be for a given note. I spent some time today hand adjusting the resonator Q values and got nice resonant (not plinky) sounds for all 55 notes. I think I may be able to get a few more this way. Then perhaps another piece of music from it since it's got quite a bit more range now.

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