On 5/6/2015 2:03 PM, Ron Roscoe wrote:
> I don't see how polarity reversal is at the same time, John. When the polarity is reversed, the two signals are 180 degrees out of phase. The negative peak in one channel is taking place at the same time as the positive peak in the other channel. That's why they cancel, given that the sine wave signals are equal in amplitude. In a polarity reversed two-channel comparison, say using 1 kHz sine wave, one channel is 0.5 msec delayed from the other channel [half the period].
Except it isn't. Think about a groove with a 1kHz signal, followed by at
10kHz signal. If it were true that the 1kHz signal, when polarity
reversed, shows an 0.5ms delay, then logically the 10kHz signal must
also be delayed by 0.5ms, which would be 5 cycles. Or, alternatively,
the delay might be different for the two frequencies. But it isn't,
because polarity reversal isn't a delay phenomenon -- it cancels
regardless of the frequency. A polarity-reversed signal *looks* like
it's delayed half a period if you look at it on an oscilloscope, but
that's an artifact of the way you choose to display it. In fact a
polarity-reversed signal is an identical, simultaneous signal which goes
up when the original goes down, and vice versa.
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