[sdiy] Ideal polyphonic digital reverb

ColinMuirDorward colindorward at gmail.com
Wed Mar 24 01:43:47 CET 2021


Enjoying these digressions, but getting back to the OT, I think the DM12
sets a good precedent for integrating reverb/FX into a polysynth, namely
because of its ability to include FX parameters in the modulation matrix.
But this is vanilla, "paraphonic" FX processing. I mentioned it before, but
the only synth I know with polyphonic FX is the EX5/r, and they are pretty
limited in scope. My ideal system (to start!) would be nothing more than a
single filter+delay line embedded after each VCA, with variables that could
be mapped in a mod matrix such as in dm12. Zipper-free time variability
would be a must-have, and I'd want a range of something like zero to 500ms.
The filter would have fixed highpass at around 80hz, plus variable high and
low shelving. The filter would be inside the feedback loop.

I  doubt there will be any consensus on the "best" reverb system. I think
it's all about what resources you have available, and what kind of user
you're targeting.

On Tue, Mar 23, 2021 at 11:10 PM David Manley <dlmanley at sonic.net> wrote:

> I don't see any free 3300 schematics online, but the block diagram here:
>
>
> http://www.analoguediehard.com/studio/effects/korg_sdd-3300/korgsdd3300-block-diagram.jpg
>
> shows an architecture that is consistent with just the sample storage
> being digital as in the SDD-3000 (the A/D and D/A or shown at the memory
> IO and not at the unit's IOs).
>
>
> On 3/23/21 7:35 PM, cheater cheater wrote:
> > Thanks, that makes more sense. How similar is the circuit for the 3000
> > to the 3300? There are no schematics for the 3300 online.
> >
> > On Wed, Mar 24, 2021 at 3:19 AM David Manley <dlmanley at sonic.net> wrote:
> >> Colin is correct - this box is filled with analog.  The delay is
> 'digital' in that samples are stored in a ram instead of some sort of
> charge storing device (like a BBD).  Beyond that and the patch storage, not
> much is digital.
> >>
> >> Check out the service manual for the schematics:
> https://www.synthxl.com/korg-sdd-3000/
> >>
> >> And to get back to the OP's question: do you mean just reverb or any
> delay effect?  An ideal reverb (and/or delay) should have a flexible
> feedback path and not just flat attenuation.  Filtering (and other
> modifiers) are very useful in the feedback path.
> >>
> >> -Dave
> >>
> >>
> >> On 3/23/21 3:54 PM, ColinMuirDorward wrote:
> >>
> >> Thanks for sharing these, Michael! I love listening to synth demos and
> music in that field.
> >>
> >> Re vintage digital delays and modern implementations, I think the
> challenge would be to recreate the analog signal paths. Many of these older
> units used analog feedback paths with filtering done in that domain. As
> well, it's likely you'd see analog companding. So for a modern remake, one
> would want to consider those aspects. I think it's low hanging fruit,
> though. There is lots to explore. I usually create my own exotic delay
> lines around a console and some budget FX units. Shelving filters work
> especially well in the feedback path, along with compressors to reign in
> unruly escalation. I'd love to try something with an above/below type
> control so I could expand below a certain threshold, and limit above a
> higher one.
> >>
> >> On Tue, Mar 23, 2021 at 9:17 PM cheater cheater <
> cheater00social at gmail.com> wrote:
> >>> Could even add more delay lines and additional I/O for eg inserting an
> >>> analog filter into feedback loops... nothing's stopping you with
> >>> today's hardware...
> >>>
> >>> What sort of feedback processing is there on the SDD-3300? No one
> >>> mentions anything like a filter, or ducking, or compression.
> >>>
> >>> On Wed, Mar 24, 2021 at 2:10 AM cheater cheater
> >>> <cheater00social at gmail.com> wrote:
> >>>> Since the SDD-3300 is all digital, it really does not sound like a
> >>>> very sophisticated algorithm - what's stopping someone from making a
> >>>> competent clone on an arduino or a small microcontroller with a few
> >>>> megs of ram?
> >>>>
> >>>> On Tue, Mar 23, 2021 at 6:02 AM Michael E Caloroso
> >>>> <mec.forumreader at gmail.com> wrote:
> >>>>> SDD-3000 is a single digital delay, no MIDI
> >>>>>
> >>>>> SDD-3300 is three digital delays with MIDI.  Complete description on
> my webpage:
> >>>>> http://analoguediehard.com/studio/effects/korg_sdd-3300/index.html
> >>>>>
> >>>>> Both are programmable.  Another difference is the LFO: four
> waveshapes
> >>>>> are available on the SDD-3000, while the SDD-3300 is triangle
> >>>>> waveshape only but each delay unit has two LFOs and the LFOs between
> >>>>> delay units can be phase offset.  That last feature is important for
> >>>>> stereo modulated delays that do not cancel in mono.
> >>>>>
> >>>>> MC
> >>>>>
> >>>>> On 3/23/21, cheater cheater <cheater00social at gmail.com> wrote:
> >>>>>> can you both tell me the difference between an sdd 3300 and an sdd
> 3000?
> >>>>>> thanks.
> >>>>>>
> >>>>>> On Tue, Mar 23, 2021 at 3:41 AM Michael E Caloroso
> >>>>>> <mec.forumreader at gmail.com> wrote:
> >>>>>>> Want more intriguing?
> >>>>>>>
> >>>>>>> MC
> >>>>>>>
> >>>>>>> On 3/22/21, James Coplin <james at ticalun.net> wrote:
> >>>>>>>> As someone with 3x SDD-3300s sitting here this intrigues me
> mightily.
> >>>>>>>>
> >>>>>>>> James R Coplin
> >>>>>>>>
> >>>>>>>> On Mar 22, 2021, 8:56 PM, at 8:56 PM, Michael E Caloroso
> >>>>>>>> <mec.forumreader at gmail.com> wrote:
> >>>>>>>>> After years of experimentation I have concluded that a polyphonic
> >>>>>>>>> synth needs both reverb and at least a pair of delays that can be
> >>>>>>>>> modulated.
> >>>>>>>>>
> >>>>>>>>> Reverb alone was never enough.
> >>>>>>>>> Modulated delays alone was never enough.
> >>>>>>>>>
> >>>>>>>>> I had really liked my Korg SDD-3300 triple digital delay for
> synths,
> >>>>>>>>> which can be configured in any series/parallel/cross-coupled
> >>>>>>>>> architecture you can dream of.  This gets better modulated
> delays than
> >>>>>>>>> multi-effect boxes.  Then I saw a spare output and two spare
> inputs on
> >>>>>>>>> the 3300, so I hooked my Lexicon PCM60 digital reverb up to it
> and
> >>>>>>>>> that was the magic combination I wanted.
> >>>>>>>>>
> >>>>>>>>> Using the 3300 I can route direct signal to reverb, then process
> the
> >>>>>>>>> reverb tales with the 3300.  Or reverb in parallel with delays.
> Or
> >>>>>>>>> series.  Add predelay to the reverb send.  Or multiple predelay
> each
> >>>>>>>>> to different delay times.  World of sounds with this combination.
> >>>>>>>>> Enough that I built seven sets of these for my synths for
> independent
> >>>>>>>>> processing.
> >>>>>>>>>
> >>>>>>>>> MC
> >>>>>>>>>
> >>>>>>>>> On 3/22/21, cheater cheater <cheater00social at gmail.com> wrote:
> >>>>>>>>>> let's enumerate some of the possibilities:
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> voice 1: vco1 -> (a1) -> vcf1 -> (b1) -> vca1 -> (c1)
> >>>>>>>>>> voice 2: vco2 -> (a2) -> vcf2 -> (b2) -> vca2 -> (c2)
> >>>>>>>>>> ...
> >>>>>>>>>> voice n: vcon -> (an) -> vcfn -> (bn) -> vcan -> (cn)
> >>>>>>>>>>
> >>>>>>>>>> at a1, you want to have one of a few things:
> >>>>>>>>>>
> >>>>>>>>>> (i) a convolution engine that takes the output of vco1, applies
> an
> >>>>>>>>> IR,
> >>>>>>>>>> and puts it into the input of vcf1
> >>>>>>>>>> (ii) same as (i) but the input is all vcos (1..n) and the
> output is
> >>>>>>>>> vcf1
> >>>>>>>>>> (iii) same as (i) but the output is all vcfs (1..n)
> >>>>>>>>>> (iv) same as (i) but the input is the last few notes you played
> in
> >>>>>>>>>> decreasing order: 1/2 * the vco from the most current note +
> 1/4 *
> >>>>>>>>> the
> >>>>>>>>>> vco from the previous note + 1/8 * the vco from the note
> previous to
> >>>>>>>>>> that etc
> >>>>>>>>>> (v) same as (iv) but you do that with the outputs
> >>>>>>>>>> (vi) same as (i) but there's also input from b1 or c1
> >>>>>>>>>>
> >>>>>>>>>> then you want the same topology at b and c
> >>>>>>>>>>
> >>>>>>>>>> They're all obviously going to have different results and
> different
> >>>>>>>>>> applications.
> >>>>>>>>>>
> >>>>>>>>>> And obviously you can think about all sorts of dsp in here, not
> just
> >>>>>>>>>> convolution, and when it comes to convolution, then not just
> reverb.
> >>>>>>>>>>
> >>>>>>>>>> On Mon, Mar 22, 2021 at 7:03 PM Mike Bryant
> >>>>>>>>> <mbryant at futurehorizons.com>
> >>>>>>>>>> wrote:
> >>>>>>>>>>> Thought I'd change the topic name as we're definitely moving
> away
> >>>>>>>>> from
> >>>>>>>>>>> cheap.
> >>>>>>>>>>>
> >>>>>>>>>>> So given a polyphonic synth with unlimited voices and unlimited
> >>>>>>>>> budget,
> >>>>>>>>>>> what should the structure of an ideal reverb system look like ?
> >>>>>>>>>>>
> >>>>>>>>>>> Once there's a consensus I'll try coding it into my digital
> synth.
> >>>>>>>>>>>
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> >>
> >>
> >> --
> >> https://www.instagram.com/colinmuirdorward/
> >> -
> >> https://www.instagram.com/ssdp_synthesis/
> >>
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