Jim wrote:
Instantaneous frequency does have a theoretical meaning, even if not
measureable..
If I'm processing a linear frequency chirp, I can say that the
frequency at time t is some (f0 + t*slope). the frequency at time
t+epsilon is different, as is the frequency at time t-epsilon.
Strictly speaking, the chirp does not have a frequency, at any time --
it has a *spectrum*. We use the mathematical fiction of "instantaneous
frequency" to express the limit as we differentiate. This is the same
as the use of the term in connection with FM modulation, and it is an
abstraction -- not something real in the world (which is why it is not
measurable, not only as a practical matter, but even in principle.)
Best regards,
Charles
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