[1000mp] ARRL REVIEW ROOFING FILTER

[Kok Chen]

On Dec 23, 2004, at 11:01 AM, Ron wrote:
> Come on now  I have been there.   There  is no  way that anyone can 
> tell the difference between -69 and -79 .  The ear is just not that 
> good.  Sorry.

Your ear might or might not detect a 10 dB difference, although 
scientific tests say that you really should.  See 
http://www.ptpart.co.uk/noise.htm.  A 10 dB change in a signal should 
sound as if it were "twice as loud."

Moreover, what we have here is even different from discerning if a 
signal itself has changed in loudness -- the case where a roofing 
filter is need is one where your brains is trying to measure the 
difference between a reference (the desired signal) and a signal you 
are comparing against (the intermod).

We are talking here of attempting to copy a signal that is +4 dB above 
the QRM versus one that -6 dB compared to the QRM.  The signal itself 
does not change, but the QRM has changed by 10 dB.  The usual accepted 
figure in the scientific world is that you can just perceive a 1 dB 
difference when there is a reference.  A 10 dB difference is huge.

73
Chen, W7AY