[sdiy] Cheapest good sounding digital reverb?

Sun Mar 21 22:32:45 CET 2021

 Polyphonic effects is something I've been waiting for the synth industry
to pick up. The closest I have is the so-called FDSP on Yahaha's EX5.

I'm not sure axoloti has enough power to run 8 independent reverbs but I
believe you can add additional A/Ds above the 2 already present. Also AFAIK
euro smith has a newer DSP engine that might be worth checking.

Personally, I would begin with a simple delay/voice. My instinct is that
this would be more interesting than full blown reverb algo, and easier to
implement.
I've been dreaming of a simple VC-pt2399 but have never tested the idea
yet. A cleaner delay with wider range delay time, right down to flanging
times, would be ideal.

Keep us posted!
Colin

On Sun, Mar 21, 2021 at 7:35 PM cheater cheater <cheater00social at gmail.com>
wrote:

> Yeah, I'm mostly looking for that sort of information about
> algorithms. Something that'll run on a small mcu while also having a
> pretty good sound.
>
> On Mon, Mar 22, 2021 at 12:09 AM Tom Wiltshire <tom at electricdruid.net>
> wrote:
> >
> > The cost isn’t the memory, so the decay time isn’t a big deal.
> >
> > The cost/quality trade-off mostly comes from the ADC/DAC, I'd say. Cheap
> convertors gives a cheap result, quality convertors gives a more expensive
> result. Mike B proposes one way of doing the conversions at very low cost.
> >
> > However, I have to say that I think a simple delay line won’t satisfy as
> a reverb. Keith Barr’s impressively simple reverbs all used other tricks
> beyond delay to make the reverb tail smoother and denser - combinations of
> allpass and delay, mostly.
> >
> > > On 21 Mar 2021, at 20:45, cheater cheater <cheater00social at gmail.com>
> wrote:
> > >
> > > Right, but what can be done regarding reverb in a small inexpensive
> > > microcontroller? Remember, we're not talking about decays of several
> > > seconds here.
> > >
> > > On Sun, Mar 21, 2021 at 6:13 PM Tom Wiltshire <tom at electricdruid.net>
> wrote:
> > >>
> > >> There isn’t much at the low-end of the DSP market, so your options
> are limited.
> > >>
> > >> There’s the FXCore, which can deal with 4 ins/4 outs, but needs
> external codecs (but that lets you choose for best quality or lowest price)
> > >>
> > >> http://www.experimentalnoize.com/product_FXCore.php
> > >>
> > >> Otherwise, you might be best moving to a bigger, faster chip and then
> expecting the one device to process 16 channels of audio for you. You’d
> still need a multi-channel codec, and the hardware is going to be all
> throughly modern and SMD-tiny!
> > >>
> > >>
> > >> On 21 Mar 2021, at 14:34, cheater cheater <cheater00social at gmail.com>
> wrote:
> > >>
> > >> It's 2-4x too expensive, but I'll check the youtube demos anyways -
> > >> thanks a lot.
> > >>
> > >> On Sun, Mar 21, 2021 at 3:23 PM Tom Wiltshire <tom at electricdruid.net>
> wrote:
> > >>
> > >>
> > >> I don’t know that it fits your definition of cheap in small volumes,
> but the Spin FV-1 chip is about your best option, I’d say. It’s a
> simple-to-use almost all-in-one option and there are loads of good reverb
> algorithms for it freely available.
> > >>
> > >> The standard application uses a cheap watch crystal (so 32KHz
> sampling) but you can run the chip faster if you need a little bit more
> hi-fi. Honestly, I doubt this is necessary for reverb. The high end is
> absorbed most quickly and hardly appears in any reverb signal. But it’s
> easy to do if required. I think the chip is specced up to 50KHz or so, and
> people have overclocked them faster than that - Spin left themselves a good
> safety margin.
> > >>
> > >> The algorithms are stored on an external EEPROM, but there are also 8
> internal programs, including several reverbs, so if you use those you can
> do without the external EEPROM, at which point it really is a one-chip
> solution.
> > >>
> > >> Check out a few FV-1 effects pedals on Youtube and see what you think.
> > >>
> > >> HTH,
> > >> Tom
> > >>
> > >> On 21 Mar 2021, at 13:19, cheater cheater <cheater00social at gmail.com>
> wrote:
> > >>
> > >> I have been thinking recently about whether it would be feasible to
> > >> have a simple reverb of some sort per voice, and so I wonder if anyone
> > >> had any suggestions on a cheap algorithm that could be executed on
> > >> inexpensive chips.
> > >>
> > >> what I need from the reverb: exponential decay of ~0.5 second, flat
> > >> frequency spectrum @ 22 Hz...22 kHz
> > >>
> > >> instrument: 16-voice
> > >>
> > >> architecture: vcos -> filters -> vca1 -> possibly vca2 (all stages
> analog)
> > >>
> > >> I'd like to be able to insert reverb after the filter but before the
> last vca:
> > >>
> > >> vcos -> filters -> vca1 -> rev -> vca2
> > >>
> > >> or possibly after the vco:
> > >>
> > >> vcos -> rev -> filters -> vca
> > >>
> > >> or after the filter:
> > >>
> > >> vcos -> filters -> rev -> vca
> > >>
> > >> or even:
> > >>
> > >> vcos -> rev1 -> filters -> rev2 -> vca -> rev3 -> vca2 -> rev4
> > >>
> > >> The reverb is meant to only "sweeten up" the sound by giving filter
> > >> sweeps, transients, and vco sweeps some more substance in the time
> > >> domain. I think this sort of thing could easily add a unique sound to
> > >> the synthesizer. I know some of you will mention the DSI Evolver, but
> > >> honestly I did not think that the digital part in that synth was of
> > >> high enough quality. So what I'm looking for is an inexpensive "hi fi"
> > >> reverb.
> > >>
> > >> The considerations are either:
> > >> A) a single chip per voice/stage which only processes one stage in one
> > >> voice. this chip would have to have high audio quality AD/DA, work
> > >> without a lot of additional circuitry, just enough processing power to
> > >> perform the reverb, and be relatively inexpensive (up to ~5 per chip
> > >> at low volumes)
> > >> B) one global chip with a bunch of AD/DA. this chip would need to be
> > >> able to read from 64 AD and write to 64 DA, each at 16 bit.
> > >>
> > >> personally I prefer A because 1. it does not carry a bunch of digital
> > >> stuff around an otherwise analog board which can be a royal pain and
> > >> 2. drifting clocks (or ones shifted on purpose) will add variety to
> > >> the sound. So those two kind of kill B for me.
> > >>
> > >> What sort of chip would you all suggest for version A?
> > >>
> > >> What algorithm would you suggest to run on it?
> > >>
> > >> Thanks.
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> > >>
> > >>
> >
>
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