In article writes:

1. How do you define "phase shift" for complex waveforms?

You don't. That's why we talk about 'group delay' instead.

2. How do you create "phase shift" for complex waveforms?

Pass it through an all-pass filer. Different frequencies that all go
in starting at the same time will come out at different times. This is
why things with "phase shift" (note the quotes) are sometimes
described as "smeary."


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In article writes:

Not quite correct, group delay just defines about the same as time shift.
For a sine wave of a specific frequency this time shift results in a phase
shift, for other frequencies the same time shift result in different phase
shifts. If this time shift or group delay depends on frequency, the effect
is called 'dispersion'. A dispersion such that all frequencies have the
same phase shift is quite a strange phenomen, for this the time shift for
20Hz should be 1000 times the time shift for 20kHz

Don't you realize how bogus this discussion is? Phase is always
relative, but you have to define what the reference is. Let's make
this as simple as we can. You have a complex waveform that's periodic
and contains a fundamental and its second and third harmonic. If they
all start at the same time, we can say they're in phase. If we apply a
delay to this waveform, it's shifted in time, so it's phase relative
to something else hasn't changed, but the frequencies comprising the
waveform are still in phase.

Now, if we pass it through a phase shift network (an all-pass filter),
each of the harmonics will be delayed by a different amount. There are
no longer in phase. Something about the complex waveform will change.

Now if we have a stereo pair of complex waveforms that are different
on each channel but have some relationship none the less - they both
came from the same source - if we delay one with respect to the other,
we'll have a whole bunch of different phase shifts, more than we can
reasonably measure, because they're going to change before we can
write the numbers down. 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.

So first we have to agree on a language,


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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

In article writes:

(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.


I can show you any number of practical (and calibrated) delays that
are likely to be lying around the studio ready to patch in. What's
a practical (and calibrated) Hilbert transformer, who has one, and how
much do they cost?

I stand by my original statement. I don't suggest that this is ALWAYS
the case, because in the lab (and on paper or computer) it's indeed
possible to construct such a device. But considering how many people
say "phase shift" and don't know what it really means, I think I'm
right, at least for those who know enough to convert between frequency
and time and know that 90 degrees is 1/4 of a cycle.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
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(Mike Rivers) writes:

In article writes:

(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.


I can show you any number of practical (and calibrated) delays that
are likely to be lying around the studio ready to patch in. What's
a practical (and calibrated) Hilbert transformer, who has one, and how
much do they cost?

I stand by my original statement. I don't suggest that this is ALWAYS
the case, because in the lab (and on paper or computer) it's indeed
possible to construct such a device. But considering how many people
say "phase shift" and don't know what it really means, I think I'm
right, at least for those who know enough to convert between frequency
and time and know that 90 degrees is 1/4 of a cycle.

Tell you what, Mike - you just believe that and don't bother your
little head about this other nonsense, OK?
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124

In article writes:

Tell you what, Mike - you just believe that and don't bother your
little head about this other nonsense, OK?

I think that's an insult, but I'm not sure. Would you try a little
harder next time?


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
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In article znr1111022720k@trad (that's me) writes:

You have a complex waveform that's periodic
and contains a fundamental and its second and third harmonic. If they
all start at the same time, we can say they're in phase. If we apply a
delay to this waveform, it's shifted in time, so it's phase relative
to something else hasn't changed,

Oops! Do-Over!

It's phase relative to something else HAS changed. Typo, but I
know someone else will catch it before this message gets posted.


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I'm really Mike Rivers )
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In article writes:

If I understand the work of Baptiste Joseph Fourier correctly, any wave
with a finite duration (has beginning and/or end) does require an infinite
number of different harmonics.

OK, but if you actually want to get anything done, you have to ignore
the impractically small ones.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
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