I am trying to take FFT of a real signal and also the output should be a real signal. Thus, I useone of these functions :
ippsFFTFwd_RToCCS_32fHowever the output signal doesn't match with the Matlab output of fft function. Any idea?
Thanks in advance
Matlab output for a length of 8 array
And by using these ippsfunctions,
ippsFFTInitAlloc_R_32f( &pSpec, 3, IPP_FFT_DIV_INV_BY_N, ippAlgHintNone );
ippsFFTFwd_RToCCS_32f(pX, pY, pSpec, pBuf);
I got these outputs:
Look at the IPP definition of CCP, you'll see it there:
As far as I know the Matlab does calculations usingDouble-Precision variables. The set of IPPSfunctions
you're using are Single-Precision ( ..._32f ). Could you submit a complete IPP Test-Case?
FFT and DFT uses different data domains (types) for efficiency purposes.
For instance, if you data is purely real, you can hold its complex version is a so-called packed domain. This is much smaller the the full complex version and thus faster (better cache utilization etc.).
However, if you print packed data, it looks not at all like normal complex data. You would have to convert packed to complex before printing it.
I don't really know useful purpose of the CCS format, but if you simply select normal complex output format, and then print that (possible first converting to real format), I'm sure your comparison would understandable.
Do you understand my text?
Not sure Matlab's out put format. But same suggestion as Thomas,
The format is as below
|Index||0||1||2||3||. . .||N-2||N-1||N||N+1|
|Pack||R0||R1||I1||R2||. . .||I(N-1)/2||RN/2|
|Perm||R0||RN/2||R1||I1||. . .||RN/2-1||IN/2-1|
|CCS||R0||0||R1||I1||. . .||RN/2-1||IN/2-1||RN/2||0|
|Index||0||1||2||3||. . .||N-2||N-1||N|
|Pack||R0||R1||I1||R2||. . .||R(N-1)/2||I(N-1)/2|
|Perm||R0||R1||I1||R2||. . .||R(N-1)/2||I(N-1)/2|
|CCS||R0||0||R1||I1||. . .||I(N-1)/2-1||R(N-1)/2||I(N-1)/2|
and you may use the Transform Functions to get real complex result.
|Function Base Name||Operation|
|ConjPack||Converts the data inPack format to complex data format.|
|ConjPerm||Converts the data in Perm format to complex data format.|
|ConjCcs||Converts the data in CCS format to complex|