Archive of the former Yahoo!Groups mailing list: MOTM

Oooh, hadn't heard of this one before. Very cool.
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Well, for lack of a better term :)

The wavetable VCO has 2 'modes':

a) you put in a 1V/Oct CV, and audio comes out. So, it's a VCO, but the
output waveshape is from scanning through a wavetable. The hardware
digitizes the CV, looks up a number in a table, and programs a digital
oscillator to output the correct frequency. Internally, the oscillator is
running 1024 times the audio output. The wavetable has 1024 points per
'cycle', so that combo generates the proper tone (in reality, it's a bit
more complicated, but this will give you the basic idea).

b) there is quite a bit of "horsepower" in the AudioEngine HW: I'm sure
without much effort the HW can output 8 simultaneous, different waveforms.
It would not surprise me that we could output over ∗100∗ different waveforms
from the FPGA gate count, but we can't get the waveform data out of Flash
that fast. This can be done over MIDI. For CVs, I'll probably make the
basic unit monophonic, then have an expansion panel for say 4 more
CVs/Outputs. It will sort of depend on how 'messy' the UI gets (I suppose
folks will want to upload/download waveforms as well). Having 5 wavetable
VCOs for <$900 total sounds like a good deal to me :)

c) the "MaxiWave" mode emulates the Blacet MiniWave. There is a dedicated
input jack for inserting a +-5V audio waveform, which is digitized to
8-bits, then the amplitude data is used as an address to "look up" an output
voltage. Since the data is 8-bit, we are 'skipping' data in the table that
would normally be outputted by the CV ('VCO mode'). However, the A/D speed
in the 'Wave Mode' needs to run ∗really fast∗ (in our case, 1Mhz!) in order
to keep up with the rapidly changing audio input (in 'VCO Mode', we still
sample pretty fast but not THAT fast, maybe 200Khz or so). When a patchcord
is inserted in the WAVE SCAN jack, the 'VCO Mode' is disabled (no, you can't
do both at the same time).

Also, the wavetables are in banks like the Blacet, and you can scan through
them with a CV as well. The on-board serial Flash is big enough to hold
1024ea wavetables, each one is 16-bits wide and 1024 points long.

The WaveTable firmware is based on the CG firmware, with the fixed sine
table 'replaced' by indexing into the serial Flash part (and no chaos, of
course).

Paul S.