Daniel, I'm not in the slightest arguing with you there, but it has been commented on in older measurement reviews that it's perhaps a bit silly to have amps with wide open responses much over 100kHz (hopefully an engineer can chip in and comment please), but with so much ultrasonic 'stuff' around in some digital sources (my Philips based CD player has 'stuff' at around the 70kHz region), any filtering has to be done very carefully, as Naim found in the mid 80's when their better preamp design had better filters put in during a model/upgrade change to replace the simpler ones they used before 'digital' sources began taking over. Ideally, a CD source should have nothing over half the sampling frequency, but I'm sure I've seen noise and 'stuff' over say, 40kHz from dacs and so on (I need clarification here though). SA-CD players had plenty of noise going on over 20kHz I remember. Couple this with metal or worse, 'diamond style' tweeters which take off at 25 - 40kHz (one seems to be +30dB at 40k compared to the mid 5 - 7kHz as we hear it level unless I'm mistaken...
DSJR, I agree with you in what you say.
What I said in #508 was just a supplement, beyond the HiFi world. Op-amps have many uses where some with high bandwidth can be good in certain, non-HiFi contexts, while the difference in bandwidth eg NE5532 vs LM4562 for audio does not matter.
Regarding sufficient bandwidth in measurements of class D amplifiers, observe measurements of, is nothing strange. You need that if you are to be able to interpret the results. If I understand that correctly that is.
Too low measurement bandwidth can result in a different result vs high measurement bandwidth as far down as 6 kHz. I think Amir uses 45 kHz when measuring class D amps.
The Nyquist frequency, if I understand it correctly, because the CD format would have a straight FR to 20 kHz, a cut off filter was needed higher up in frequency. Nyquist's theoretical ideas were then applied, which became part of the solution for the CD format, the CD technology.Which became the standard solution that all manufacturers used.
Don't ask me to elaborate. I'm out on thin ice now with a lack of my technical knowledge on this subject. Might be worth a new thread to sort it out.
(if there aren't already such threads)