Computes the signal energy distribution in the joint time-frequency domain by using the short-time Fourier transform (STFT) algorithm.
Configuration of the FFT size of the STFT. This input determines the number of columns in the output STFT spectrogram.
This input is available only if you wire a waveform or a 1D array of double-precision, floating-point numbers to x.
A Boolean that determines whether to coerce the frequency bins to a power of 2. If this input is True and the frequency bins is not a power of 2, this node sets the frequency bins to the nearest power of 2.
True | Coerces the frequency bins to a power of 2. |
False | Does not coerce the frequency bins to a power of 2. |
Default: True
A Boolean that determines whether to exclude the energy at the Nyquist frequency from the output STFT.
True | If the FFT size of the STFT is even and this input is True, the output STFT does not include the energy at the Nyquist frequency. |
False | Includes the energy at the Nyquist frequency. |
If the FFT size of the STFT is odd, this node ignores this input.
Default: True
The density to use to sample the signal in the joint time-frequency domain and to define the size of the resulting 2D time-frequency array.
This input changes to time steps if you wire a double-precision, floating-point number to x.
Number of samples to shift the sliding window. When this input is less than or equal to zero, this node adjusts this input automatically so that no more than 512 rows exist in output STFT.
Performance Considerations
If you specify a small value for time steps, the node might return a large spectrogram, which requires a long computation time and more memory. NI recommends you set time steps so that the number of rows in STFT spectrogram does not exceed 512. If you need a small sampling rate to observe more details and the signal length is large, divide the signal into smaller segments and compute the spectrogram for each segment.
Default: -1
FFT size of the STFT. If this input is less than or equal to zero, this node sets the input to 512. If this input is 1, this node coerces the input to 2.
Default: 512
Number of samples to shift the sliding window. time steps must be greater than 0.
This input changes to time-frequency sampling information if you wire a waveform or a 1D array of double-precision, floating-point numbers to x.
Performance Considerations
Increasing time steps decreases the computation time and reduces memory requirements but also reduces time-domain resolution. Decreasing time steps improves time-domain resolution but increases the computation time and memory requirements.
Default: 1
Information about the window to use to compute the STFT.
Type of window to use to compute the STFT.
Name | Value | Description |
---|---|---|
Rectangle | 0 | Applies a rectangle window. |
Hanning | 1 | Applies a Hanning window. |
Hamming | 2 | Applies a Hamming window. |
Blackman-Harris | 3 | Applies a Blackman-Harris window. |
Exact Blackman | 4 | Applies an Exact Blackman window. |
Blackman | 5 | Applies a Blackman window. |
Flat Top | 6 | Applies a Flat Top window. |
4 Term B-Harris | 7 | Applies a 4 Term B-Harris window. |
7 Term B-Harris | 8 | Applies a 7 Term B-Harris window. |
Low Sidelobe | 9 | Applies a Low Sidelobe window. |
Blackman Nuttall | 11 | Applies a Blackman Nutall window. |
Triangle | 30 | Applies a Triangle window. |
Bartlett-Hanning | 31 | Applies a Bartlett-Hanning window. |
Bohman | 32 | Applies a Bohman window. |
Parzen | 33 | Applies a Parzen window. |
Welch | 34 | Applies a Welch window. |
Kaiser | 60 | Applies a Kaiser window. |
Dolph-Chebyshev | 61 | Applies a Dolph-Chebyshev window. |
Gaussian | 62 | Applies a Gaussian window. |
Force | 64 | Applies a Force window. |
Exponential | 65 | Applies an Exponential window. |
Default: Hanning
Length of the window in samples. When you wire a waveform or a 1D array of double-precision, floating-point numbers to x, this node sets the input to 64 if length is less than or equal to zero. When you wire a double-precision, floating-point number to x, length must be greater than 0 and less than or equal to the sample length.
Default: 64
Length of each set of data. The node performs computation for each set of data.
sample length must be greater than zero.
This input is available only if you wire a double-precision, floating-point number to x.
Default: 100
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Standard Error Behavior
Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.
Default: No error
A value that affects the output coefficients when window type is Kaiser, Gaussian, or Dolph-Chebyshev.
If window type is any other type of window, this node ignores this input.
This input represents the following information for each type of window:
This input is available only if you wire a waveform or a 1D array of double-precision, floating-point numbers to x.
Default: NaN—Causes this node to set beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window
A Boolean that determines whether to scale the STFT spectrogram so that the energy in the joint time-frequency domain equals the energy in the time domain.
True | Scales the STFT spectrogram so that the energy in the joint time-frequency domain equals the energy in the time domain. |
False | Does not scale the STFT spectrogram so that the energy in the joint time-frequency domain equals the energy in the time domain. |
Default: True
A 2D array that describes the time waveform energy distribution in the joint time-frequency domain.
Error information.
The node produces this output according to standard error behavior.
Standard Error Behavior
Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.
To compute the output STFT Spectrogram, this node completes the following process.
The following figure shows the procedure this node uses to compute the STFT.
If the input force freq bins to power of 2? is True and the input frequency bins is not a power of 2, then the following equation holds true:
where $\left[\right]$ is the nearest operation.
Otherwise, K is equal to frequency bins.
If the result of the STFT is the matrix $\text{STFT}\left\{X\right\}$, then the size of $\text{STFT}\left\{X\right\}$ is M-by-K, where the following are true:
You can use the $\text{STFT}\left\{X\right\}$ to approximate the energy in the joint time-frequency domain using the following expression:
This result almost equals the energy in the time domain, as shown in the following expression:
After computing the STFT of X, this node computes the STFT spectrogram of X. This node calculates the STFT spectrogram as the magnitude square of the elements in $\text{STFT}\left\{X\right\}$. Because the FFT returns symmetric results, this node calculates the STFT spectrogram only on the left half of $\text{STFT}\left\{X\right\}$, as shown in the following equation:
where the following are true:
Where This Node Can Run:
Desktop OS: Windows
FPGA: This product does not support FPGA devices
Web Server: Not supported in VIs that run in a web application