[sdiy] Cheapest good sounding digital reverb?

[Tom Wiltshire]

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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