Hi,
I'm trying to create an aliasing free multiplication of two signals.
As far as I remember from my days at the university (long time gone) a
multiplication in the time domain can be replaced by / is the same as a
convolution in the frequency domain.
And the convolution can help to avoid aliasing.
So for testing I create 2 band limited signals in the frequency domain
that don't lead to aliasing when multiplied and converted them to the
time domain wit an fft and multiplied them to have a reference.
Then my program does a convolution of the two buffers in the frequency
domain with the very raw C++ code below. And everything works fine until
one of the buffers contains a signal at the first frequency bin (freq=0).
Probably I've got a big misunderstanding of "convolution in the
frequency domain" or even worse - theres just a bug in my convolution code.
Thanks in advance for any help,
Thomas
float * CConvTest::ConvolutionInF(float * pfA, float * pfB, long lSize)
{
memset(m_pFConvDest, 0, lSize * sizeof(float));
for(long ixa = -lSize + 1; ixa < lSize; ixa ++)
{
float fA = pfA[abs(ixa)];
for(long ixb = -lSize + 1; ixb < lSize; ixb ++)
{
long ixDest = ixa + ixb;
if(ixDest >= 0 && ixDest < lSize)
m_pFConvDest[ixDest] += fA * pfB[abs(ixb)];
}
}
return m_pFConvDest;
}
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