Quote:
Originally Posted by GaryM
OK, I'll try to illustrate this.
Imagine the bottom two waves shown are the signals from two microphones.
In the left-hand example the two waves are in-phase and combine to create the wave at the top (the same sound twice as loud), and in the right-hand example the two waves are out-of-phase and combine to create silence.
In the right-hand example, the top wave of the pair at the bottom could be gotten by reversing the polarity one one of the microphones, in effect inverting the waveform. But imagine instead of turning the waveform upside-down, that you slid the original wave sideways, until the peaks on one wave lines up with the troughs on the other. You would end up with the same result as inverting the wave, except this time you would have shifted the wave by 180 degrees. This is why a 180 degree phase shift is regarded as the same as inverting the polarity of a wave. |
YES, i understood this already, yes...
my point "180 degrees out of phase" and "polarity reversed"
are not equivalent. if you have two microphones on a source reverse the polarity on one, it is going to sound drastically different from delaying the signal until it is 180 degrees out of phase, perhaps this will work with a constant frequency and amplitude. but if we're talking about a guitar amp, this doesn't work. if you gradually increase the gap between the two you get a sort of comb filtering effect, but the two will never cancel out in the same way reversing the polarity will, because 180 degrees out of phase at 50hz is different to 180 degrees at 1k.
I've just made sure i'm not mad and tried it on some guitars that i recorded today. I'm right, it sounds totally different. Yes you do get a certain amount of cancellation but its not the same, they sound different, very different.
But yes, i understand that if you had a constant 50hz sine wave and you put another one 180 degrees out of phase with it, they would cancel each other out.