[sdiy] Cheapest good sounding digital reverb?

Mon Mar 22 14:16:25 CET 2021

Teensy 4.1 with a multi-channel I/O (6 in / 8 out) using Cirrus Logic
CS42448 codec:
https://blog.oshpark.com/2017/05/01/tdm-support-for-many-channel-audio-io/

For basic Schroeder type reverberator you will need quite a lot RAM for the
delay lines though...

https://ccrma.stanford.edu/~jos/pasp/Freeverb.html

On Mon, Mar 22, 2021 at 9:42 AM Vladimir Pantelic <vladoman at gmail.com>
wrote:

> check the reverb that's part of Mutable Instruments Clouds. IIRC it uses
> very
> little CPU and memory and can be easily adapted to run standalone.
>
> On 3/22/21 12:31 AM, cheater cheater 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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