jargon
On Sat, 19 Nov 2011 03:11:23 -0800 (PST), Dick Pierce
wrote:
On Nov 19, 12:12*am, "
wrote:
RichD
wrote:
On Nov 18, " wrote:
What's the difference between reverb, echo, and feedback?
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?
Aren't they all delay?
Different delay (and decay). If the delay is on the order of a wavelength and
shorter than the decay, it's feedback.
Wrong.
Disagree.
Feedback requires two conditions: first, the delay
must be an integral multiple of a wavelength (or complete
phase rotations: essentially equivalent)
No, it can be sub-wavelength. Half wavelength would essentially be negative
feedback. There is no reason why feedback must be exactly in phase.
and second, the
system must have a power gain equal to or greater than one.
To regenerate, sure. There was nothing here about regeneration.
Feedback cannot occur unless both conditions are present.
Oscillation cannot occur unless the gain at 360degrees is greater 1. Feedback
certainly can.
The requirement of gain in the system is what makes feedback
very different than either echo or reverb.
You're conflating "feedback" and "oscillation" (regenerative feedback).
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.
Ok, I'll buy that regeneration can occur at 1 wavelength.
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.
^^^^^^^^^^^^^^^^^^^^
Oscillation stops but feedback continues
There's still feedback, but without the necessary gain,
the system no longer oscillates.
Ok, you've admitted that you're confusing feedback and oscillation.
Greater than that it's reverb
So, is there some specific delay value in which you claim
that an echo becomes reverb?
When you can hear it, but not discern the individual images (echo). There is
obviously a gray area there.
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