Dear Steve,
in general you cannot have 1 Hz resolution by analyzing only 100 ms
worth of signal. A simple way of looking at it is that you are only
fitting one tenth of a 1 Hz waveform in your window. So by only looking
at the waveform through your narrow window you cannot know whether the
waveform repeats, say, every 1 s or every 200 ms.
If you want to have a FFT with 1 Hz resolution every 100 ms what you can
do is to have 1 s long sliding window (e.g. first FFT is 0.0 - 1.0 s,
second FFT is 0.1 - 1.1 s, etc.) This obviously requires changing the
FFT size (and 1 M sample FFT is quite large).
I think the correlation approach you propose is similar to doing FFT on
a 100 ms window that has been zero-padded to 1 s. Indeed you get 1 Hz
frequency bins, but their content is effectively only an interpolation
between 10 Hz bins. You gain no new information.
However, if you can make some assumptions about the signal you are
analyzing (for example, you know that there is only a single tone
between 1 and 10 Hz), then some kind of correlation or curve-fitting
approach might work better than FFT.
Best regards
Tomaž
On 06. 11. 2017 16:42, Steve Gough wrote:
Hi all,
Could you please help answer a quick signal processing question ? I
apologize if this is the wrong mailing list.
I have a sampling rate of 1M samples/second, and I perform an FFT every
100ms. This gives me a frequency resolution of 10Hz (i.e. each bin size
is 10Hz). Is there any way I can increase my frequency resolution (say
from 10Hz to 1Hz) without changing the FFT size ?
If I "manually" correlate different frequency sinusoids (1Hz sinusoid,
2Hz sinusoid etc) with the samples acquired in the 100ms duration, can
this give me a higher frequency resolution (1Hz in the above case) ?
Thanks in advance!
Steve
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