[time-nuts] Tbolt issues

Charles Steinmetz csteinmetz at yandex.com
Fri Sep 2 02:12:08 EDT 2016

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,


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