How do I test if the PreOuts of my AVR or the power amplifiers are clipping?

[anphex]

Hello everyone!
I was watching The Hobbit yesterday and there were short clipping sounds in some places. These were parts where there was actually little bass. But it could also be that there were already frequencies in the range of 20 Hz, which I just did not notice.

My current assumption is that the preouts of the Denon have caved in, since the level was already at -7dB and there were large volume jumps during the film. My power amps are two 425 watt Audiphonics Purifi monoblocks on 85db/1W speakers. The speakers also handle the bass.

 

[Tony_in_PA]

What is the input to the Denon? Are you saying the volume of the Denon was set to -7 dB? It seems odd to me that the Denon would clip its preouts if the input signal is something standard coming from the source. The Denon should be engineered to output any "standard" signal that's input to it. So unless you are amplifying an analog signal before feeding it into the Denon analog inputs it should be able to reproduce the signal on the preouts with some margin.

There may be other tricks that I don't know, but you could pass a known frequency into the Denon and measure distortion on the preouts or visually check the signal with an oscilloscope. I assume you are much more likely able to measure distortion with the sound card of a computer (using the line in jack) and REW than you are to have a scope.

If the preouts are clipping there should be very obvious distortion. The more the smooth tops of the sine wave get chopped off the worse the distortion will be. The extreme case is a square wave which will produce the largest magnitude harmonics of the fundamental frequency. Using REW's RTA function to look at the signal in the frequency domain should show this. See below.

How to - Distortion Measurements with REW

I have been using the excellent and free software package called REW and a sound interface card (or DAC/ADC) to measure my amps for years now. It’s fast, easy and really costs nothing if you have a sound interface already. REW is normally used for measurement of speakers with microphones...

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