On Apr 30, 7:21 am, Rune Allnor <all...@tele.ntnu.no> wrote:
> On 28 Apr, 18:20, Andy <andya...@gmail.com> wrote:
>
> > I'm doing some DSP for radar applications.  My background in DSP is
> > limited, so I'm trying to get up to speed.
>
> > Performing a circular rotation to move the beginning of data to the
> > center of the dataset before a FFT and then rotating back after seems
> > to be routine (almost taken for granted).  Can anyone explain the
> > benefit of this when compared to just a straight FFT of the data?
>
> As others already indicated, a lot of this is a matter
> of personal taste or established convension in particular
> fields.
>
.> However, in the case of radar and sonar, it might
.> make a certain sense to organize the spectrum with
.> DC near the middle. Human users might find it easier
.> to spot and interpret Doppler shifts in such plots.
.>
.> Rune

That's a good example. but not because it is radar and sonar but
because it is a case where the processed band has been complex
demodulated to baseband and contains frequencies both higher and lower
than what is now represented by DC. That is almost always true in
radar and active sonar. In passive sonar, audio and music the signal
is often real with no different information on one side of DC than the
other. Even in the bandpass cases, where you want to put DC may depend
on whether or not the sidebands are symmetric.

Dale B. Dalrymple

On Apr 30, 10:21&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
> On 28 Apr, 18:20, Andy <andya...@gmail.com> wrote:
>
> > I'm doing some DSP for radar applications. &#4294967295;My background in DSP is
> > limited, so I'm trying to get up to speed.
>
> > Performing a circular rotation to move the beginning of data to the
> > center of the dataset before a FFT and then rotating back after seems
> > to be routine (almost taken for granted). &#4294967295;Can anyone explain the
> > benefit of this when compared to just a straight FFT of the data?
>
> As others already indicated, a lot of this is a matter
> of personal taste or established convension in particular
> fields.
>
> However, in the case of radar and sonar, it might
> make a certain sense to organize the spectrum with
> DC near the middle. Human users might find it easier
> to spot and interpret Doppler shifts in such plots.
>
> Rune

Thank you Dale and Rune for the suggestions.  I think that canceling
the Doppler shifts may just be the key here.

On 28 Apr, 18:20, Andy <andya...@gmail.com> wrote:
> I'm doing some DSP for radar applications. &#4294967295;My background in DSP is
> limited, so I'm trying to get up to speed.
>
> Performing a circular rotation to move the beginning of data to the
> center of the dataset before a FFT and then rotating back after seems
> to be routine (almost taken for granted). &#4294967295;Can anyone explain the
> benefit of this when compared to just a straight FFT of the data?

As others already indicated, a lot of this is a matter
of personal taste or established convension in particular
fields.

However, in the case of radar and sonar, it might
make a certain sense to organize the spectrum with
DC near the middle. Human users might find it easier
to spot and interpret Doppler shifts in such plots.

Rune

On Apr 28, 9:20 am, Andy <andya...@gmail.com> wrote:
> I'm doing some DSP for radar applications.  My background in DSP is
> limited, so I'm trying to get up to speed.
>
> Performing a circular rotation to move the beginning of data to the
> center of the dataset before a FFT and then rotating back after seems
> to be routine (almost taken for granted).  Can anyone explain the
> benefit of this when compared to just a straight FFT of the data?
>
> Thank you
>
> Andy

Writing in terms of time series at the input:

Do you prefer to view t=0 at the start of the array or in the middle?
Do you prefer to get DC out at the start of the array or in the
middle?
How does your fft function behave?

Rotate as necessary.

Dale B. Dalrymple

I'm doing some DSP for radar applications.  My background in DSP is
limited, so I'm trying to get up to speed.

Performing a circular rotation to move the beginning of data to the
center of the dataset before a FFT and then rotating back after seems
to be routine (almost taken for granted).  Can anyone explain the
benefit of this when compared to just a straight FFT of the data?


Thank you

Andy