[sdiy] Cheapest good sounding digital reverb?

Mon Mar 22 14:38:51 CET 2021

PCB's can be found here:
https://oshpark.com/shared_projects/gVFy0fWQ

Teensy 4.1 for an example has Cortex-M7 chip (Freescale) running at 600 MHz
and having 1MB of RAM (512 kB tightly coupled).
https://www.pjrc.com/store/teensy41.html

On Mon, Mar 22, 2021 at 3:31 PM Mikko Helin <maohelin at gmail.com> wrote:

> The latest Teensy 4.x version of the CS42448 board adds an extra A/D for
> total 8 channels of audio input:
>
> https://hackaday.io/project/2984/logs
>
>
> On Mon, Mar 22, 2021 at 3:16 PM Mikko Helin <maohelin at gmail.com> wrote:
>
>> 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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>>> >
>>>
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>>
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