[sdiy] FPGA based Synth....

[Scott Gravenhorst]

James Patchell <patchell at cox.net> wrote:
>Hey...got some more done on the FPGA based synth...(well, synth might be 
>exaggerating a bit),,,
>
>
>I now have 16 oscillators, 16 VCA's and 16 simple ASR type envelope 
>generators (with RC type shape to the envelope...ie... 1 - exp(t/T) )....It 
>is pretty cool...
>
>I ordered a proto board from Digilent for my Spartan 3E Starter Kit...On 
>it, I will put an anti-alias filter, a midi interface, an interface 
>connector for the AVR STK501/500 board, some LEDs...and I will have a 
>simple Midi digital synth.
>
>As soon as I can I will post the Verilog code, schematics, etc...it looks 
>like it uses up about 30,000 gates worth in a Spartan III....and right 
>now...It does all sixteen voices in 21 clocks.

Very interesting.  I've also been working on an FPGA synth.  MIDI controller works
(PicoBlaze) and controls a 2 NCO FatMan emulator (monosynth for now).  It's almost
finished, I'm bumping it up to 4 NCOs.  The NCOs are microtunable via a shared
interpolating tuning LUT.  The filter is a single stage IIR type and is tunable as in
sweepable and is controlled by an ADSR as is the NCA.  Portamento is implemented using
another IIR filter that employs no multipliers.  Sample clock is 1 MHz so no anti alias
filter is required.  The synth currently uses about 10% of the FPGA on the Spartan-3E
Starter Kit.  I've also gotten pitch noise modulation to work.  Modulation paths can be
connected to any MIDI CC.  Oh and Jim, I'm using your UART code for MIDI, attribution is
in the source.


-- ScottG

---------------------------------------------------------
-- Scott Gravenhorst
-- Xilinx Spartan-3E Based Music Synthesizers
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/