[sdiy] Midiverb reverse engineer project?

[Tim Ressel]

Yep, its all the the algorithm. There is no compression or anything in 
the hardware.

To switch between midiverb and midifex: I wonder if you could solder one 
eeprom on top of the other and simply break out the chip select and 
output enable pins?

On the algorithm: I know there are the FV-1 algorithms out there, but 
I'd be interested in seeing the midiverb code.

On the hardware: yes I know we don't actually need the hardware to 
figure out the algorithm. But Mr. Barr's accomplishment is amazing 
enough to warrant the effort.

Personal note: I worked at Alesis for a short period during the midiverb 
days. So this is a bit of a nostalgia trip for me.

--tr


On 10/18/2016 8:46 AM, Kenji Garland wrote:
> On the hardware side, I'd be interested to learn whether there's 
> anything very special about the Midiverb line's A/D converters. I love 
> sampling synths through a Midiverb II with its input sensitivity 
> cranked, and I've never been sure if the Midiverb did any distinctive 
> clipping to make that arrangement sound so good, or if it was just the 
> magic algorithms as others have suggested.
>
> Kenji
>
>
> On Tue, Oct 18, 2016 at 9:33 AM Richie Burnett 
> <rburnett at richieburnett.co.uk <mailto:rburnett at richieburnett.co.uk>> 
> wrote:
>
>     As far as I know it's all in the reverb algorithms.  Some of the later
>     Midiverb used the general purpose micro (that handles MIDI and the
>     UI) to
>     poke new coefficient values into the DSP part on the fly to do
>     modulation
>     effects like flange and chorus, and also to add a bit of movement
>     to break
>     up the metallic ringing in long reverb tails.  Keith Barr has been
>     quite
>     open about the design and algorithms of the Midiverb in various online
>     forums.
>
>     As I understand it, the FV-1 is Keith's result of distilling down
>     the bare
>     essentials of what makes a good reverb, and then designing a "DSP"
>     chip
>     optimised for this task.  For instance it has hardware sine/cosine
>     LFO's,
>     and can implement things like linear interpolation and allpass
>     filters using
>     just a pair of special instructions tailored to chorus/reverb
>     generation.
>
>     -Richie,
>
>
>     -----Original Message-----
>     From: Tom Wiltshire
>     Sent: Tuesday, October 18, 2016 2:02 PM
>     To: Mikko Helin
>     Cc: Synth-Diy
>     Subject: Re: [sdiy] Midiverb reverse engineer project?
>
>
>     On 18 Oct 2016, at 11:56, Mikko Helin <maohelin at gmail.com
>     <mailto:maohelin at gmail.com>> wrote:
>
>     > You don't need to reverse engineer the hardware, the sound is in the
>     > algorithms I guess.
>
>     Is that right? Did any of the early units do anything special on
>     the analog
>     side? Compander or tone filters or anything? I don't know anything
>     about the
>     Alesis reverb units, and I never owned one.
>
>     Aside from that sort of pre/post processing, I agree - you should
>     be able to
>     take a recent basic DSP and recreate it exactly. Doing it on an
>     FV-1 would
>     be a nice touch, since Keith Barr designed that chip.
>
>     Tom
>
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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