If it quacks like a duck…

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Daniel von Recklinghausen, the renowned audio engineer at EAD and KLH is famous for this old chestnut:

“If it measures good and sounds bad, — it is bad. If it sounds good and measures bad, — you’ve measured the wrong thing.”

Hard to argue with the man’s logic.

One of the ways I like to think about problems is to turn them on their head. If we agree we can hear things we cannot measure, what are the things we can measure and hear?

One of the easiest is how an amplifier responds to square waves. Take a look at the two square wave responses of power amplifiers from Stereophile. (the amp names have been suppressed to protect the innocent).

The first image shows pretty severe ringing or overshoot on the leading edge of the 10kHz square wave. The second image is nearly perfect.

What can we tell from this simple measurement? Amplifier number one will likely have a brightness to music where amplifier two will not.

What’s interesting is that classic measurements of these two amplifiers, like THD and IM, would tell us next to nothing about how they sound. Yet this scope view tells a great deal of what to expect.

I’ve put together a little video on what we can hear through measurements here.