What’s Wrong with this Signal?

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At the Consumer Electronics Show in 2001, the display at this vendor’s booth stopped me cold. Apart from putting all that money into a booth display without bothering to spell-check it (Individual Multiple Stands?), there was the “Before” picture of a signal, degraded by the ill-judged use of some competitor’s signal cable.

Ixos says, “signal arcing between conductors giving the music a coarse characteristic” produces the trace of the graph. I say, “BS”. Ignore the clipping displayed and pay attention to the flatline periods at 0V. I admit that it took me several months and a discussion with an audio engineer at an Acoustical Society of America meeting to work out what could cause this sort of signal, but that it wasn’t the proffered “signal arcing” was immediately obvious. I’ve used just about every conceivable grade of multi-strand wire to hook up test equipment, including stuff so corroded as to be *almost* worthless, and I’ve never seen a signal of the sort they display as the “Before” graphic.

Maybe some of you folks won’t take so long as I did to work out what actually could produce the signal shown there given a sinusoidal input. Have a go at it.

Wesley R. Elsberry

Falconer. Interdisciplinary researcher: biology and computer science. Photographer. Husband. Christian. Activist.

2 thoughts on “What’s Wrong with this Signal?

  • 2006/10/27 at 9:25 pm

    It’s a class-b amplifier with bad crossover bias, and peak clipping. Used to be common in PNP-NPN transistor output stages. Now I think people use FETs that don’t have this problem.

  • 2006/10/28 at 12:04 am

    Excellent. I’d never had to work with those types of amps, which meant I had led a sheltered existence, at least so far as diagnosing what the heck the Ixos people were supposedly going on about. If your signal looks like what they show on their display, simply changing cables over to Aptimus brand stuff won’t do diddly to fix the problem.

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