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 Kyma Forum
 Confabulation
 Negative Frequencies
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| Author | Topic: Negative Frequencies |
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Larry Simon Member |
posted 16 August 2005 13:26
 
This is a general signal processing question rather than a Kyma-specific one, but I thought I'd ask anyway if anyone wants to comment. It concerns the complex fourier transform vs. the real. Do they produce identical results (i.e. are the negative frequencies in the complex case irrelevant) if we assume that we don't have any aliasing going on, or do the negative frequencies still carry useful information of some kind? IP: Logged |
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SSC Administrator |
posted 16 August 2005 14:15
The negative frequency information is useful only if you are analyzing complex signals (that is, the signal is made up of a real and an imaginary part). If the signal is real (which is the ordinary case), the negative frequency spectral components are the complex conjugate of the positive frequency spectral components (this means that the real part is the same but the imaginary part is the negation -- another way to view it is that the negative frequency phase is the negative of the positive frequency phase information). Since the negative frequency spectral components can be easily computed from the positive frequency components, they add no extra information and can be ignored. Keep in mind that this is true for real signals only and that you definitely need to supply the negative frequency spectral components to the inverse transform in order to reconstruct a proper real signal. IP: Logged |
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Larry Simon Member |
posted 02 September 2005 10:11
Thanks for the quick, clear response. -Larry IP: Logged |
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