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Old 30th January 2006, 06:25 PM   #1
Wizard of Kelts
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Default Reverb Controls-Can You Filter Out Original Signal Entirely?

My question is about reverb, usually a pro item, even though the application is for a home system.

I would like a cheap delay system for speakers. I see plenty of used reverb units on the market.

Reverb is what happens when the original signal is delayed a certain amount, and the delayed signal then rejoins the original signal.

I see controls for ms of delay on the reverb, but my question is this: is it common for these reverb units to allow you to eliminate the original signal entirely, so that only the delayed signal comes through?

I would think that a control that varies the relative amount of original signal versus delayed signal might do this-if the original signal knob has a zero setting. Similar to a balance signal on an amp.

Is that pretty much a normal feature?
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Old 30th January 2006, 07:01 PM   #2
dnsey is offline dnsey  United Kingdom
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It's certainly quite easy to do that, and most decent delay units have the facility. It's commonly used for time domain compensation in big PA rigs, etc.
However, is it really what you really want? Reverb re-introduces a portion of the 'wet' signal into the delay line to give the familiar effect. If you filter the input signal from the output, you will just have a delayed signal, with no 'interesting' characteristics.
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Old 30th January 2006, 07:06 PM   #3
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I think you want a delay unit rather than a reverb. reverb has many delay times which are mashed together. a delay only has 1 or a lownumber (and u can disable the other ones) most modern effects units can do both anyways. and they have a dry/wet control which mixes between the original and processed signal.
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Old 30th January 2006, 07:08 PM   #4
dnsey is offline dnsey  United Kingdom
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Sorry - just re-read your post, and I see that IS what you want!
The frequency response and signal to noise level of cheap units is pretty poor - not hi-fi by any means!
I suggest that you contact your local pro audio dealer and discuss second-hand delay units (rather than reverbs). As I mentioned, these are used for time compensation - very similar to your application - but it depends how much you want to spend, and whether you want to pay that much.
You could always DIY, of course - it's a relatively simple matter to make up a shift register based delay unit.
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Old 30th January 2006, 08:43 PM   #5
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Default Re: Reverb Controls-Can You Filter Out Original Signal Entirely?

Quote:
Originally posted by kelticwizard
I see controls for ms of delay on the reverb, but my question is this: is it common for these reverb units to allow you to eliminate the original signal entirely, so that only the delayed signal comes through?
It is common as far as I know. It's not uncommon for (unpoor) guitarists to run one amp dry and one amp wet to get a bigger sound.
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Old 31st January 2006, 12:54 AM   #6
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Quote:
Originally posted by neutron7
reverb has many delay times which are mashed together. a delay only has 1 or a lownumber (and u can disable the other ones)....
So you're saying that if I cut the original signal, my delayed signal will not be pure, but a reverb of of several delays mixed together?
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Old 31st January 2006, 01:13 AM   #7
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Hi Pete

Ok, brief rundown of reverb. The process works by continually feeding back a decreasing amount of signal into the delay circuit, via various EQ and volume settings. The delay setting you see, is properly called predelay, and allows the reverb to be made more realistic by delaying the sound of the reverb effect an appropriate amount of time to suit the space being simulated, i.e. a big hall will have greater predelay than a small room, because it takes the sound a certain amount of time to reach the walls and be reflected.

Does that make sense?
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Old 31st January 2006, 01:54 AM   #8
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Al:

Yes. The reverbs are built to recreate the experience of hearing the sound first ounce off the floor, then off one wall, then off the other, then off the ceiling, then off the back wall, etc etc.

So reverbs are out for simple delay purposes.

dnsey wrote:
Quote:
It's certainly quite easy to do that, and most decent delay units have the facility. It's commonly used for time domain compensation in big PA rigs, etc.
Al recommended these units as well. After a few day's checking on Ebay, however, I have yet to come across one-at least that I know.

Online stores which sell pro gear pretty much know what they have and charge accordingly. The prices are sharply reduced-but reduced from an original price of $1000 or more. Pro gear is expensive, partly because it has to be extremely durable and reliable, partly because when you're living relies on a piece of equipment, you don't quibble about price nearly as much as a consumer would.

I am seeing home delay units for quite reasonable on Ebay-people getting rid of their old stuff from the eighties and even earlier. That wouldn't bother me much, but the problems are:

A) They work only for two channels-the project requires four.

B) The delays don't seem to be separately adjustable for each channel. Left and right channel gets the same delay.

Problem A) can be resolved by buying two delay units.

Problem B) can possibly be due to the fact that, since delay mechanisms seem to be voltage controlled, the unit simply feeds the same voltage to each channel's delay mechanism. A few minutes disconnecting the stock voltage feed and installing two opamp circuits might be all that is required.

While I haven't built a full size amp or preamp, I have built signal generators, etc. I can set up and solder in a small opamp into a piece of existing equipment for a voltage feed-that much I can do.

Still, I would like to buy a ready-made unit before modifying anything. That's why I thought I would ask about the reverb units, which seem to be easy to come by. Apparently, however, not a good idea.
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Old 31st January 2006, 02:06 AM   #9
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You might be better off just getting a new Behringer DCX.
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Old 31st January 2006, 02:37 AM   #10
Brion55 is offline Brion55  United States
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I own two DigiTech Studio S-100s which allow the "dry" signal to be turned off. It has mulitple pre-set reverbs and controls to customize them to your own taste. The S-100 has two engines which can be configured in several ways, including true stereo. A very nice unit for about $150.
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