[sdiy] Cheapest good sounding digital reverb?

[Tom Wiltshire]

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 <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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