multiple-type Digisound VCDO thing?

[David Halliday (Volt Computer)]

> -----Original Message-----
> From:	WeAreAs1 at aol.com [SMTP:WeAreAs1 at aol.com]
> Sent:	Monday, April 28, 1997 6:47 PM
> To:	synth-diy at horus.sara.nl
> Subject:	multiple-type Digisound VCDO thing?
> 
> a-davidh at microsoft.com (David Halliday) wrote:
> 
> << I am asuming that you are taking a VC oscillator, running it
> through some
> kind of address generator and clocking address lines of an EPROM - you
> have
> waveshapes loaded in EPROM which are D/A'd and sent out. >>
> 
> Yes, that is correct.
> 
> << Just off the top of my head, you could probably run an adder
> circuit
> between the address lines - cycle the other adder input with a slowly
> varying
> input from a VC Digital Low Freq Osc...  This would give you a varying
> phase
> shift between the two ( or more ) signals. >>
> 
> Yeah, you could, but at that point you would be spending more money
> and
> effort than you would have by simply using another 3340 as a second
> voltage-controlled clock, don't you think?  Besides, it's the
> flexibility and
> elasticity of voltage control that gives the VCDO its main appeal.
> The adder
> circuit idea wouldn't be nearly as flexible as plain ol' voltage
> control,
> IMO.
> 
> 
> BUT... <grin>  Your two outputs would be locked together.  You would
> enter one CV for the frequency and one CV for the phase difference
> between the two outputs.  Using two seperate CV's for two seperate
> oscillators would mean that they would not track "perfectly" and that
> you couldn't precicley control the phase relationship between the two
> outputs...  Wether this is desirable musically or not...  <g>
> Another idea would be to build this as a two-oscillator board with two
> 3340's but to be able to switch it from two seperate DVCO's to one
> DVCO with DVC-Phase
> 
> 
> << You could carry this even further by having the DLFO clock another
> EPROM
> with various vaveshapes in it... >>
> 
> DLFO?  You've lost me here.  Do you mean VC clock?  The clock runs at
> a
> fairly high frequency (probably the sampling rate of the EPROM data),
> and is
> what's used to clock the address generator.  Are you talking about
> using an
> LFO to switch thru different wave addresses, as can be done on a Wave
> PPG?
>  This, under voltage control, would be fun..  If this is what you
> mean, how
> would you accomplish this?
> 
> 
> Digital Low Frequency Oscillator - you would want control extending
> down to the 0.01Hz range and probably anything beyond the 1,000Hz
> range wouldn't be really useful for anything ( talking pahse control
> here... ) except ring-mod and percussive noises...
> 
> 
> 
> << Another thing is that you could use a much bigger EPROM and
> manually
> switch the upper address bits to select different waveshapes. >>
> 
> Yep.  If the basic wave data length is short enough, you could fit
> quite a
> few of these waves in a *big* EPROM.  Each wave would have its own
> manually
> selected "meta-address".  Furthermore, I think it would be very
> interesting
> if you could devise some kind of clocked/toggled meta-address, which
> would
> switch between two user-selected meta-addresses at the wave half-cycle
> point.
>  (Yes, I really do think this would sound good, or at least weird.  In
> a good
> way.)  Kind of like a digital half-wave rectfier, except that the
> "rectified
> half of the wave could be another completely different wave.
> 
> 
> 
> This is interesting too!!!  It would be simple to implement since the
> high-order bit toggles exactly halfway through the waveform...  Use
> that to select another "table"
> 
> Say if you have 12 address lines, eight of them ( 0 through 7 ) are
> used for wave clocking and the remaining four are used to select one
> of 16 different waveshapes...  You could then use a simple flip-flop
> on the high-order bit to toggle between two of the 16 banks for the
> top and the bottom waveshape.
> 
> There has been mention here last week about doing the same thing with
> Analog oscillators and the comment was that it was good...  Hmmm....
> 
> 
> 
> 
>