Signal Processing Blockset™

Short-Time FFT - Compute nonparametric estimate of spectrum using short-time, fast Fourier transform (FFT) method

Library

Transforms

dspxfrm3

Description

The Short-Time FFT block computes a nonparametric estimate of the spectrum. The block buffers, applies a window, and zero pads the input signal. Then, the block takes the FFT of the signal, transforming it into the frequency domain.

Connect your sample-based or frame-based, single-channel analysis window to the w(n) port. For the Analysis window length parameter, enter the length of the analysis window, W. When your analysis window is a sample-based signal, the block buffers it into a frame-based signal with frame length W. When your analysis window is a frame-based signal and its frame length is not W, the block buffers the signal so that its frame length is W.

Connect your sample-based or frame-based, single-channel or multichannel input signal to the x(n) port. After the block buffers and windows this signal, it zero-pads 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 complex-valued, sample-based, single-channel or multichannel short-time FFT is output at port X(n,k).

The Short-Time FFT block supports real and complex floating-point and fixed-point signals.

Fixed-Point Data Types

The following diagram shows the data types used within the Short-Time FFT subsystem block for fixed-point signals.

The settings for the fixed-point parameters of the Array-Vector Multiply block in the diagram above are as follows:

• Rounding Mode — Floor

• Overflow Mode — Wrap

• Product output — Inherit via internal rule

• Accumulator — Inherit via internal rule

• Output — Same as first input

The settings for the fixed-point parameters of the FFT block in the diagram above are as follows:

• Rounding Mode — Floor

• Overflow Mode — 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 Array-Vector Multiply block reference pages for more information.

Examples

The dspstsa_win32 demo illustrates how to use the Short-Time FFT and Inverse Short-Time FFT blocks to remove the background noise from a speech signal.

Dialog Box

Analysis window length

Enter the frame length of the analysis window.

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.

References

Quatieri, Thomas E. Discrete-Time Speech Signal Processing. Englewood Cliffs, NJ: Prentice-Hall, 2001.

Supported Data Types

See Also

See Power Spectrum Estimation for related information.

Selector

Signal From Workspace