[Arny Krueger]

"geoff" wrote in message


Don Pearce wrote:

Using Audition, I created two seconds of white noise. I
selected half of it and imposed a first order lowpass
filter that hit -1.8dB at 20kHz (what an amplifier would
be, more or less). Then I played it as a repeating loop,
and could hear the cyclic change of tone.

No way could I have heard it with music, of course.

Sure you weren't hearing the envelope of average power
content dropping ?


Good point. My simulations suggest that this effect is on the order of 2 dB.

Another point is that a filter that is about 2 dB down at 20 KHz is 1 dB
down at 15 KHz, and maybe 0.5 dB down at 10 KHz.

The effects of first order filters are so broad as to be about useless in an
evaluation like this.

[Don Pearce]

On Sun, 10 Feb 2008 17:51:20 -0500, "Arny Krueger"
wrote:

"geoff" wrote in message
m

Don Pearce wrote:

Using Audition, I created two seconds of white noise. I
selected half of it and imposed a first order lowpass
filter that hit -1.8dB at 20kHz (what an amplifier would
be, more or less). Then I played it as a repeating loop,
and could hear the cyclic change of tone.

No way could I have heard it with music, of course.

Sure you weren't hearing the envelope of average power
content dropping ?


Good point. My simulations suggest that this effect is on the order of 2 dB.

Another point is that a filter that is about 2 dB down at 20 KHz is 1 dB
down at 15 KHz, and maybe 0.5 dB down at 10 KHz.

The effects of first order filters are so broad as to be about useless in an
evaluation like this.


We're forgetting where this came from. I used a first order filter
because that is what the top end of a power amplifier response tends
towards - this wasn't an exercise to see what drop I could hear at
20kHz.

If somebody can plot the actual response of the Behringer amp, and it
turns out to be other than first order, I will give that a go.

d

--
Pearce Consulting
http://www.pearce.uk.com