Quasi-Reverb (NOT quasiverb!)

[The Dark force of dance]

Y-ellow Erik 'n' Y'all.
At 11:40 AM 10/2/97 +0200, Erik Schuijers wrote:
>Hi everyone,
>
>another idea sprang of my mind! I'm thinking of building a quasi-reverb by
>using the digital delay line on Batz's page. My main idea is:
>               +---+     +----+
>            +--| a |-----| RC |--------------+
>            |  +---+     +----+              |
>            |                                |
>            +--|\        ----------------    |
>               | \ ______| Dig. D. Line |----+-- Audio out
>               | /       ----------------   
> Audio in -----|/Summing
>                   Amp
>
>The idea is to use the output of the digital delay line again as an input
>signal. To get that 'real' verb effect you could use a simple RC-filter to
>filter out higher order components. The amplification 'a' could be adjusted
>to alter the amount of feedback.

This just gives a flanging effect. If the delay is long enough it will give
a sort of echo-flange. It will not produce reverb. To produce reverb you
need a multi-tap delay. The more taps the smoother the reverb. In the real
world, Reverb could be considered to be thousands of delays. Each one a
different time factor. Some so slightly different to the next that phasing
does occur. Which in most digital reverb units is accounted by an actual
flange/phase effect to cut down on the actual number of delay taps required.
Then to create the illusion of stereo the mono reverb effect is phase
inverted to one of the channels before bing mixed back with the original
signal. It isn't actually stereo but it does a good impersonation. Devises
such the cheaper alesis microverbs and nanoverbs do this. More expensive
reverb units do a mathematical calculation to produce a theoretical reverb.
It is possible therefore to inject a signal into a room which can be
analyzed such that the room's reverb can be sampled. I'm not sure if the new
CoolEdit does this yet but David Johnston was talking about including it.

It would be possible to take that digital delay circuit and modify it with
multiple taps but you would need to substantially change the logic to do so.
It's real purpose is to illustrate the principals of Sigma/Delta modulation.

Hope this helps.

Be absolutely Icebox.
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