ShortTime FFT
Nonparametric estimate of spectrum using shorttime, fast Fourier transform (FFT) method
Library
Transforms
dspxfrm3
Description
The ShortTime FFT block computes a nonparametric estimate of the spectrum. The block buffers, applies a window, and zero pads the input signal. The block then takes the FFT of the signal, transforming it into the frequency domain.
Connect your singlechannel analysis window to the w(n) port. For the Analysis window length parameter, enter the length of the analysis window, W. The block buffers the input signal such that it has a frame length of W
Connect your singlechannel or multichannel input signal to the x(n) port. After the block buffers and windows this signal, it zeropads the signal before computing the FFT. For the FFT length parameter, enter the length to which the block pads the input signal. For the Overlap between consecutive windows (in samples) parameter, enter the number of samples to overlap each frame of the input signal.
The block outputs the complexvalued, singlechannel or multichannel shorttime FFT at port X(n,k).
FixedPoint Data Types
The following diagram shows the data types used within the ShortTime FFT subsystem block for fixedpoint signals.
The settings for the fixedpoint parameters of the ArrayVector Multiply block in the diagram above are as follows:
Rounding Mode —
Floor
Saturate on integer overflow —
Wrap
Product output —
Inherit via internal rule
Accumulator —
Inherit via internal rule
Output —
Same as first input
The settings for the fixedpoint parameters of the FFT block in the diagram above are as follows:
Rounding Mode —
Floor
Saturate on integer overflow —
Wrap
Sine table —
Same word length as input
Product output —
Inherit via internal rule
Accumulator —
Inherit via internal rule
Output —
Inherit via internal rule
See the FFT and ArrayVector Multiply block reference pages for more information.
Examples
The dspstsa
example
illustrates how to use the ShortTime FFT and Inverse ShortTime FFT blocks to remove
the background noise from a speech signal. To open the dspstsa
model,
type dspstsa
in the MATLAB^{®} command prompt.
Parameters
 Analysis window length
Specify the frame length of the analysis window. The Analysis window length must be a positive integer value greater than one.
 Overlap between consecutive windows (in samples)
Enter the number of samples of overlap for each frame of the input signal.
 FFT length
Enter the length to which the block pads the input signal.
Supported Data Types
Port  Supported Data Types 

x(n) 

w(n) 

X(n,k) 

References
[1] Quatieri, Thomas E. DiscreteTime Speech Signal Processing. Englewood Cliffs, NJ: PrenticeHall, 2001.
Extended Capabilities
Version History
See Also
Objects
Blocks
 Spectrum Estimator  Inverse ShortTime FFT  Magnitude FFT  Periodogram  Spectrum Analyzer  Window Function  YuleWalker Method