Magnitude FFT (DSP Blockset)

DSP Blockset

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Magnitude FFT

See Also

Compute a nonparametric estimate of the spectrum using the periodogram method.

Library

Power Spectrum Estimation, in Estimation

Description

The Magnitude FFT block computes a nonparametric estimate of the spectrum using the periodogram method. For input u,

y = abs(fft(u,nfft)).^2      % equivalent MATLAB code

where N_fft is specified as a power of 2 by the FFT size parameter. A value of -1 for FFT size instructs the block to use the input frame size as the FFT size. Otherwise, the block zero pads or truncates the input to N_fft.

The input is an M-by-N frame matrix, with each of the N frames containing M sequential time samples from an independent signal. The Number of channels parameter specifies the number of independent signals, N, in the matrix.

The block computes a separate periodogram for each of the N independent channels in the input, generating an N_fft-by-N matrix output. Each column of the output matrix contains the estimate of the corresponding input column's power spectral density at N_fft equally spaced frequency points in the range [0,F_s), where F_s is the signal's sample frequency.

Dialog Box

FFT size: The number of data points on which to perform the FFT, N_fft. If N_fft exceeds the input frame size, the frame is zero-padded as needed.
Number of channels: The number of channels (columns) in the input matrix, N.

References

Oppenheim, A. V. and R. W. Schafer. Discrete-Time Signal Processing. Englewood Cliffs, NJ: Prentice Hall, 1989.

Proakis, J. and D. Manolakis. Digital Signal Processing. 3rd ed. Englewood Cliffs, NJ: Prentice-Hall, 1996.