Or, now that I think about it, it's similar to what we do when
measuring ADEV.. you can do a crude "how many zero crossings in the
time window" or you can do a "fit a sinusoid to a series of ADC
samples". One has an uncertainty of "one count/epoch", the other
can be substantially better.
How could it be substantially better for the same analysis period?
Unless the frequency under test is an integral number of periods
during the analysis period, you will have a variation in the sine
fitting due to starting phase.
OTOH, as admonished in Horowitz & Hill, if the frequency to be
counted is substantially below your counter timebase, then you should
count zero crossings of the higher timebase frequency in the period
of the lower frequency under test.
Dr. David McClain
Chief Technical Officer
Refined Audiometrics Laboratory
4391 N. Camino Ferreo
Tucson, AZ 85750
email: [email protected]
phone: 1.520.390.3995
web: http://refined-audiometrics.com
On Oct 13, 2010, at 22:30, jimlux wrote:
Jim Lux wrote:
That's not precisely true. You can get a frequency estimate that
is substantially more precise than 1/T if the snr is high.
Consider super-resolution in an interferometer which is
mathematically similar. What you give up is ambiguity. Probably
one of the oldest techniques is that of Prony, but there are lots
of others
Or, now that I think about it, it's similar to what we do when
measuring ADEV.. you can do a crude "how many zero crossings in the
time window" or you can do a "fit a sinusoid to a series of ADC
samples". One has an uncertainty of "one count/epoch", the other
can be substantially better.
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