[Fpga-synth] "TerrorMouse" progress

[Scott Gravenhorst]

I started playing with the ideas in the TerrorMouse synth document. 
Judging from my experiments, with my Spartan-3E SK FPGA, I should be able
to make a maximum of 10 waveguides using block RAM 18 bits wide.  However,
I need one block RAM for the MIDI controller and at least one multiplier,
so I'm hoping for 8 note polyphony.  If I understood access to the on board
SDRAM, I could easily make that more.  So I will have to learn how to do that.

The waveguide experiments I've done are with a 1024 element waveguide in a
C program that generates an output response given a pulse or other
waveshape excitation.  I use 'sox' to create a .wav from the raw file so I
can listen.  That's where the fun started.  I can change waveguide length,
filter bandwidth, exciter pulse width and shape and the position of the
"pickup" (which is the sum of a point on both arrays equidistant from the
bridge).  What I'm hearing says that several different kinds of sounds can
be made with this simple system.  I got drums (like bongo and conga), some
things similar to bells and gongs, and what sound very much like metalic
strings.  All in all, the sounds all have a "natural" sort of sound.  They
don't sound exactly like "something", but they can sound close.  IMO this
is good enough to see how this works in a synth.

The terrormouse document cites a 256 element waveguide and that the upper
register (3rd octave? I didn't do the math) had tuning problems.

If I use a 1024 element waveguide, I calculate I should get a minimum of 3
octaves of very good tuning, possibly 4.  Good enough for me.

So that's the _start_ of where I'm going with this.

-- ScottG

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-- Scott Gravenhorst
-- GateMan I - Xilinx Spartan-3E Based MIDI Synthesizer
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.