How to interpret phase in REW? - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-26-11, 04:17 AM Thread Starter
Shackster
jbjb

Join Date: Jun 2009
Posts: 35
How to interpret phase in REW?

Below is the REW graph for my subs. I'm interested in knowing how to read the phase graph in particular, especially what do those few vertical lines mean?

Can anyone shed some light on this?
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Old 02-26-11, 05:37 AM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,303
Re: How to interpret phase in REW?

Phase is cyclic, due to the periodicity of the sine function. When it is increasing and reaches 180 degrees it wraps around to -180 and continues with -179, -178 etc. When it is decreasing and reaches -180 degrees it wraps around to 180. The vertical lines show those wrap points. If you look in the graph controls you will see a button to "unwrap" the phase, which allows it to go to 181, 182 etc rather than wrapping, but you can end up with extremely large value ranges in unwrapped phase, partly because any time delays create a frequency-dependent phase shift that gets ever larger as frequency increases.
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Old 02-26-11, 10:04 PM Thread Starter
Shackster
jbjb

Join Date: Jun 2009
Posts: 35
Re: How to interpret phase in REW?

Thanks for the info John. I'm still trying to "wrap" my head around phase.

My graph above is for 2 subs combined. So at the wrap points does it means the frequencies cancel each other?
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Old 02-27-11, 04:48 AM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,303
Re: How to interpret phase in REW?

No, all that changes at the wrap points is the way the graph is drawn. Think of it more like reading the second hand of a clock, after 59 secs it starts again at 0 and counts up again, but time has not jumped or done anything other than progress as usual. The part of phase that gets plotted when wrapping is used is like showing only the seconds of a time.
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