Mixing
Why are patterns repeated in the frequency-power graph of a periodic signal?
$begingroup$
I have a signal, which I'd like to treat as a non-continuous function now, let it be $signal(t)$. It looks like this:
Zoomed in a bit:
I create a Lomb-Scargle Periodogram using $signal(t)$, which I understand to be very similar to non-uniform FFT (that is to say, the $t$s for which $signal(t)$ is defined, are not always separated by equal distance - as it is the case now).
The computed plot, frequency vs power:
I am happy with the large peak on the left side of the plot, but I am confused about the peaks centered around 48. Zoomed in on those:
They seem to be a reflection of the peaks on the left. I suspect that it is something to do with the Nyquist frequency. The difference between largest and smallest $t$ is around $27.8$, and I have around $1280$ values of $t$ (nearly but not exactly equidistance from each other), so the sampling rate is $1280/27.8 approx 46$. This is closed to the previously observed $48$, but also clearly distinct from it (ie the previously observed 48 was an approximation, not an exact value, but it was definitely not $46$).
How can I explain this peculiarity of the frequency-power plot of this function?
This question was also posted here.
fourier-analysis fourier-transform signal-processing
asked Feb 2 at 18:47
zabopzabop
2029
$endgroup$
add a comment |
$begingroup$
I have a signal, which I'd like to treat as a non-continuous function now, let it be $signal(t)$. It looks like this:
Zoomed in a bit:
I create a Lomb-Scargle Periodogram using $signal(t)$, which I understand to be very similar to non-uniform FFT (that is to say, the $t$s for which $signal(t)$ is defined, are not always separated by equal distance - as it is the case now).
The computed plot, frequency vs power:
I am happy with the large peak on the left side of the plot, but I am confused about the peaks centered around 48. Zoomed in on those:
They seem to be a reflection of the peaks on the left. I suspect that it is something to do with the Nyquist frequency. The difference between largest and smallest $t$ is around $27.8$, and I have around $1280$ values of $t$ (nearly but not exactly equidistance from each other), so the sampling rate is $1280/27.8 approx 46$. This is closed to the previously observed $48$, but also clearly distinct from it (ie the previously observed 48 was an approximation, not an exact value, but it was definitely not $46$).
How can I explain this peculiarity of the frequency-power plot of this function?
This question was also posted here.
fourier-analysis fourier-transform signal-processing
asked Feb 2 at 18:47
zabopzabop
2029
$endgroup$
2
$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00
add a comment |
$begingroup$
I have a signal, which I'd like to treat as a non-continuous function now, let it be $signal(t)$. It looks like this:
Zoomed in a bit:
I create a Lomb-Scargle Periodogram using $signal(t)$, which I understand to be very similar to non-uniform FFT (that is to say, the $t$s for which $signal(t)$ is defined, are not always separated by equal distance - as it is the case now).
The computed plot, frequency vs power:
I am happy with the large peak on the left side of the plot, but I am confused about the peaks centered around 48. Zoomed in on those:
They seem to be a reflection of the peaks on the left. I suspect that it is something to do with the Nyquist frequency. The difference between largest and smallest $t$ is around $27.8$, and I have around $1280$ values of $t$ (nearly but not exactly equidistance from each other), so the sampling rate is $1280/27.8 approx 46$. This is closed to the previously observed $48$, but also clearly distinct from it (ie the previously observed 48 was an approximation, not an exact value, but it was definitely not $46$).
How can I explain this peculiarity of the frequency-power plot of this function?
This question was also posted here.
fourier-analysis fourier-transform signal-processing
asked Feb 2 at 18:47
zabopzabop
2029
$endgroup$
I have a signal, which I'd like to treat as a non-continuous function now, let it be $signal(t)$. It looks like this:
Zoomed in a bit:
I create a Lomb-Scargle Periodogram using $signal(t)$, which I understand to be very similar to non-uniform FFT (that is to say, the $t$s for which $signal(t)$ is defined, are not always separated by equal distance - as it is the case now).
The computed plot, frequency vs power:
I am happy with the large peak on the left side of the plot, but I am confused about the peaks centered around 48. Zoomed in on those:
They seem to be a reflection of the peaks on the left. I suspect that it is something to do with the Nyquist frequency. The difference between largest and smallest $t$ is around $27.8$, and I have around $1280$ values of $t$ (nearly but not exactly equidistance from each other), so the sampling rate is $1280/27.8 approx 46$. This is closed to the previously observed $48$, but also clearly distinct from it (ie the previously observed 48 was an approximation, not an exact value, but it was definitely not $46$).
How can I explain this peculiarity of the frequency-power plot of this function?
This question was also posted here.
fourier-analysis fourier-transform signal-processing
fourier-analysis fourier-transform signal-processing
asked Feb 2 at 18:47
zabopzabop
2029
asked Feb 2 at 18:47
zabopzabop
2029
asked Feb 2 at 18:47
zabopzabop
2029
asked Feb 2 at 18:47
zabopzabop
2029
asked Feb 2 at 18:47
zabopzabop
2029
2029
2
$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00
add a comment |
2
$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00
2
2
$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00
$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00
add a comment |
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$begingroup$
Probably have you had a look at this document : arxiv.org/pdf/1703.09824.pdf Besides, you don't mention the software you use...
$endgroup$
– Jean Marie
Feb 2 at 19:00