[sdiy] Ideal polyphonic digital reverb

David Manley dlmanley at sonic.net
Wed Mar 24 04:07:21 CET 2021


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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