[sdiy] Midiverb reverse engineer project?

[Kenji Garland]

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>
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> 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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