5bee2351   
   XPost: sci.electronics.basics   
      
   On Sat, 19 Nov 2011 03:11:23 -0800 (PST), Dick Pierce   
    wrote:   
      
   >On Nov 19, 12:12 am, "k...@att.bizzzzzzzzzzzz"   
   > wrote:   
   >> RichD    
   >> wrote:   
   >>   
   >>> On Nov 18, "k...@att.bizzzzzzzzzzzz"  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.   
      
   --- SoupGate-Win32 v1.05   
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