[Arny Krueger]

"Ian Iveson" wrote in
message k
Phil wrote:

Well, remember, the maximum slew rate found in audio
signals is much
greater than what a theoretical 20 KHz signal is going
to supply,

Yes and no, Phil.

Take 20kHz at full amplitude to define the required slew
rate.
Add another identical signal, in phase.

You now have twice the slew rate, as you think.

But the signal is also twice full amplitude, so it is not
comparable.
To make it comparable, you must reduce it to full
amplitude.
In so doing, you halve the slew rate, returning it to its
original value.

Hence adding these signals together doesn't alter the
slew rate, as long as the total signal remains within the
defined full amplitude.

Agreed.

Does this logic hold for the sum of a full amplitude
20kHz and some other, lower frequency? Intuitively yes,
to me. A bit of simple trig would confirm.

The math supports your intuition.

What about smaller signals? Well, they will never have a
higher slew rate than the 20kHz at full amplitude, surely?

As long as they are band-limited to 20 KHz.

The agenda that seems to be hidden from Phil relates to the vast improvement
in the bandwidth of power transistors over the years. In the 60s and early,
large power devices used in power amps usually ran out of gas below 1 MHz.
Today for about the last 20 years, parts that beat that by a factor of 10 or
more are plentiful and inexpensive.