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FourSerCosCoeff


Unit:SDL_fourier
Class:TFastFourier
Declaration:property FourSerCosCoeff[n: integer]: double;

The readonly array property FourSerCosCoeff returns the coefficients An of the cosine terms of the Fourier series (cf. to equation below). The index n may assume values between 0 and SpectrumSize div 2. Accessing any value of the array below 0 and above SpectrumSize will result in a zero value on read, or in no action on write.

By using the above equation and the properties FourSerSinCoeff and FourSerCosCoeff the original curve can be reconstructed after a Fourier transform has been performed (of course, an inverse transform would do the same).

Hint 1: In order to obtain "valid" results the property WeightingWindow has to be set to fwRectangle.

Hint 2: Mind the subtle difference between the Magnitude and the Fourier series coefficients. The Magnitude does not preserve the signs, while the properties FourSerSinCoeff and FourSerCosCoeff do.

Hint 3: FourSerCosCoeff could be easily calculated from RealSpec by adding the coefficients of the corresponding negative and positive frequencies.

Hint 4: The index n into the property starts from zero (as opposed to the other array properties)

Example: This property is used in the following example program (see http://www.lohninger.com/examples.html for downloading the code): fft



Last Update: 2012-Oct-20