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90 degree phase offset in CoolEdit
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Randy Yates
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(Mike Rivers) writes:
I believe that when someone says "I've shifted
the left channel 90 degrees from the right channel" nearly all the
time, they'll mean that they've created that phase shift at a single
frequency, typically near mid-band, with some sort of a delay.
I disagree. What I think they mean is that they have passed the stereo
input signal through the following system:
Xr --------------------------- Yr
--------
Xl --------| H(w) |---------- Yl
--------
where H(w) is a practical Hilbert transformer. Note the ideal Hilbert
transformer has H(w) = -j * sgn(w), where w = 2*pi*f, and sgn(x)
denotes the signum function,
sgn(x) = +1, x 0,
0, x = 0,
-1, x 0.
See, e.g., Stefan Hahn's "Hilbert Transforms in Signal Processing."
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124
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