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RealSpec


Unit:SDL_fourier
Class:TFastFourier
Declaration:property RealSpec[ix: integer]: double;

The array property RealSpec provides access to the real part of the spectrum. The index ix may assume values between 1 and SpectrumSize. Accessing any value of the array below 1 and above SpectrumSize will result in a zero value on read, or in no action on write.

Note: Since the index of the data buffer starts with 1 (and not 0), the index of the harmonics of the resulting Fourier spectrum is shifted by one. Thus the constant coefficient a0 is stored in RealSpec[1], the first harmonic in RealSpec[2], the second in RealSpec[3], and so on.

Hint: In order to obtain the coefficients of the cosine terms of the corresponding fourier series, one has to add up the positive and the negative frequency (see also FourSerCosCoeff).

The figure below shows the order of the frequency components as they are stored in RealSpec after performing a Fourier transform:

Example: This property is used in the following example programs (see http://www.lohninger.com/examples.html for downloading the code): fft60hz, fft, foursynt, ftfilter



Last Update: 2012-Oct-20