Short-time Fourier Transform
"STFT" computes a time-frequency distribution of an input
signal x within a given frequency interval as a sequence of
short-time spectra of windowed signal segments with constant
This function returns a 2D signal of the adaptive time-frequency
spectrum. It is displayed as time (x-axis) versus frequency (y-axis) with the
power or amplitude spectral values given on the z-axis.
Parameters of "STFT" are
- lower frequency f0 in reciprocal x-axis units,
- upper frequency f1 in reciprocal x-axis units,
- fres, which is the output resolution of the frequency
axis (number of points),
- tres, which is the output resolution of the time axis (number of points)
- window size N (length of a signal segment) in samples,
- spectrum type (spectype), which is either
- "Power" (0) or
- "Amplitude" (1)
- type of normalization (normtype), which is either
- "Absolute Power/Amplitude" (0),
- "Spectral Density" (1) or
- "Maximum Norm" (2).
There is always an inherent tradeoff between time resolution and frequency resolution with being the sampling period (scale) of the signal. It can be expressed by the uncertainty relationship . Thus, the appropriate choice of N strongly depends on the scale (i.e. the sampling period) and the characteristics of the signal to be analysed.
signal x, y;
float f0, f1;
int fres, tres, N;
option spectype, normtype;
Note that y is a 2D signal.
Momentary ARMA spectrum, Multiscale TFD.