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RE: Dynamics Measured....

Posted by tomservo on April 23, 2017 at 07:40:00:
Hi Jim
I am glad you posted here, you should have a good selection of toys.

I had not heard of the scissors test but I did find the peak levels indicated by the 2204 slm on impulse hold, were a lot louder than the subjective loudness would have suggested.

A problem is our sense of loudness is both frequency and time weighted and not strictly sound pressure like a microphone but if one wants to produce "the whole signal", one has to produce all of it.

Not knowing what / if any integration was in the meter on impulse hold, the cumbersome / failsafe way to judge instantaneous peak pressure is to capture the mic signal on a storage scope (or a repetitive signal is easy to capture on a regular scope) and use the mic sensitivity to calculate the peak pressure.

Lastly on the subjective audibility of very short things;
About 15 years ago, a well known amplifier company was going around with an abx box and their new amplifiers.
They came to the shop and from home I brought in my trusty Threshold stasis intended to be in the mix.

I set up a system I was familiar with and had a CD of wave files (of to me were revealing and difficult recordings). We had Crown's, a Chevin, the QSC's and a few others. Fast forward 6 hrs and the amps generally had two slightly different sounds, it was all very subtle behavior on the decay side of transients and only audible on a few tracks but repeatable. AND then there was the Threshold.
It sounded exactly the same as the better category amps but at a decent but not that loud level (on sensitive speakers) it sometimes was less dynamic.
Enough different that I grabbed an oscilloscope and looked at the amp outputs (as the front indicators said we were at peaks about -16dB) and saw that on the biggest peak, there was occasional instantaneous clipping.

It was these very short "limiting" events which were it, not at all audible as traditional "clipping" but instead were only detectable when you heard with and without as I was here, being able to switch to a much larger amplifier and back.
Since then I have urged people if they have a scope, to look at the amp signal (perhaps not with class D) and see if there is any clipping at listening levels.
Best
Tom