jargon

What's the difference between reverb, echo, and feedback?

-- Rich

Reply to
RichD
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Reverberation is the persistence of sound in a particular space after the original sound is removed.[1] A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air.

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A reflected sound that is heard again by its initial observer.

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Sound created when a transducer such as a microphone or electric guitar picks up sound from a speaker connected to an amplifier and regenerates it back through the amplifier.

--
JF
Reply to
John Fields

"Rich Dope"

** Depends on the context.

Digital delays and tape echo machines have controls with these names.

... Phil

Reply to
Phil Allison

Or, in an electrical circuit, when the voltage or current at a point in the circuit is "fed back" to a point earlier in the circuit. Depending on its phase, this can be either negative or positive feedback.

--
Virg Wall
Reply to
VWWall

Delay

Reply to
krw

Aren't they all delay?

-- Rich

Reply to
RichD

Different delay (and decay). If the delay is on the order of a wavelength and shorter than the decay, it's feedback. Greater than that it's reverb until you can distinguish the individual images. Then it's echo. ...at least that's how I see it.

Reply to
krw

Echo is a single reflection of a sound - the kind you hear when you shout "Hello" near a cliff.

If you put together many echoes, arriving from different distances into a jumble that you can't distinguish - that is reverb. You get that in, say, a large church.

Feedback is a situation you only get when you have an amplifier and a speaker. The sound arriving from the speaker is a little louder than the one that originally hit the microphone, so that comes out of the speaker a little louder still. This loop will build until the system howls. You cure it by turning down the amplifier so the sound from the speaker is always a little softer than the original when it hits the microphone.

d
Reply to
Don Pearce

Multiple reflections are also common in such instances.

That would be *acoustic feedback* only, There are MANY other types of course.

Or any other method that reduces the loop gain at the feedback frequency, notch filtering being a common example.

Trevor.

Reply to
Trevor

No they are not. One cliff, one echo. No choice.

In the context of the question it would simply be confusing to discuss

- or even mention - other kinds.

Again, given the question, no need to complicate the answer.

d
Reply to
Don Pearce

Perhaps we might ask the original poster what is meant by "reverb" and "echo" and "feedback."

By "echo" and "reverb," do you mean the acoustical phenomenon of echo and reverberation? Or do you mean the analog or digital effects (simulations, if you will) often labelled "echo" and "reverb"?

"Feedback" is, in some ways, an effect that's in a different class. But all systems with a connection between the output and the input are capable of having feedback, By "feedback," are you talking about when a system, breaks into self-oscillation, which means positiive, regenerative feedback?

h and

Wrong. Feedback requires two conditions: first, the delay must be an integral multiple of a wavelength (or complete phase rotations: essentially equivalent) and second, the system must have a power gain equal to or greater than one. Feedback cannot occur unless both conditions are present. The requirement of gain in the system is what makes feedback very different than either echo or reverb.

The notion that feedback requires a delay on the order of a wavelength is easily shown to be false when one observes acoustical feedback in amplified PA systems happening at middle frequencies (several hundred to several thousand Hertz) where the amplifier and speaker are quite some distance apart, many dozens of feet, where the corresponding delay between the two corresponds to many wavelengths.

In such a situation, one very quick cure is to turn the volume down: this reduces the overall gain of the system to less than 1, and the regnerative feedback then stops. There's still feedback, but without the necessary gain, the system no longer oscillates.

So, is there some specific delay value in which you claim that an echo becomes reverb?

--

+--------------------------------+
  • Dick Pierce |
  • Professional Audio Development |
+--------------------------------+
Reply to
Dick Pierce

The original post sounded like a homework question.

Reply to
sgordon

I'm not so sure. The feedback part was too far out of kilter with the rest for any real physics teacher to have set it.

d
Reply to
Don Pearce

I was thinking of a recording class in a music department.

In rec.audio.tech Don Pearce wrote: : On 19 Nov 2011 16:40:38 GMT, snipped-for-privacy@changethisparttohardbat.com : wrote: : >The original post sounded like a homework question. : I'm not so sure. The feedback part was too far out of kilter with the : rest for any real physics teacher to have set it. : d

Reply to
sgordon

Ah. That probably makes it worse, not better.

d
Reply to
Don Pearce

That is positive feedback. Feedback is not always positive.

If there is a lot of distance between the speaker and microphone, you can hear echos rather than howls.

Feedback can be (but does not have to be) used for generating echos and reverbs in effect units or software.

In digital effects units, feedback is used to make it look like there is more RAM. Rather than computing all echoes from the original input function (which requires enough RAM to store a window of sound representing the longest echo time) the echos are faked by taking the output and feeding a fraction of it back to the input. The same is done for faking long reverbs.

I have an old Yamaha unit here from 1989 which has only a 700 ms delay, but the reverb can be cranked to 40 seconds, haha. Any sample you hear beyond

700 ms, related to the original signal, has already been through the digital mill and is reappearing via feedback. Accordingly, the reverb starts to sound like crap beyond 2 seconds.

A honestly modeled 40 second reverb would actually have an impulse response sample of 40 seconds from a nice sounding hall, and use a 40 second window of the input to do the convolution.

Reply to
Kaz Kylheku

Disagree.

No, it can be sub-wavelength. Half wavelength would essentially be negative feedback. There is no reason why feedback must be exactly in phase.

To regenerate, sure. There was nothing here about regeneration.

Oscillation cannot occur unless the gain at 360degrees is greater >1. Feedback certainly can.

You're conflating "feedback" and "oscillation" (regenerative feedback).

Ok, I'll buy that regeneration can occur at > 1 wavelength.

^^^^^^^^^^^^^^^^^^^^ Oscillation stops but feedback continues

Ok, you've admitted that you're confusing feedback and oscillation.

When you can hear it, but not discern the individual images (echo). There is obviously a gray area there.

Reply to
krw

Two walls of said cliff; multiple echoes. If you're on the edge of the cliff with no opposing wall there will be zero echo.

But you found it necessary to bring up loop gain. Interesting. You wouldn't be an audiophool, by chance?

Reply to
krw

Since when does one cliff have two walls? The cliff IS the wall.

Loop gain greater than unity is what causes feedback howl. There is no way of avoiding it if you want to explain what causes the feedback. And make no mistake, the feedback the OP was asking about was the loud howl you get when you turn the PA up too far.

d
Reply to
Don Pearce

Zero intelligence.

Wrong. *Regenerative* feedback needs a gain > unity.

You can't even keep *your* terms straight. You *must* be an audiophool (lack of an answer speaks volumes).

Reply to
krw

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