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**Owning Palette:** Time Frequency Spectrogram VIs

**Requires:** Advanced Signal Processing Toolkit

Computes the short-time Fourier transform (STFT)-based spectrogram of **signal**. Wire data to the **signal** input to determine the polymorphic instance to use or manually select the instance.

STFT spectrogram is the most effective and widely used quadratic time-frequency analysis method. However, the time-frequency resolution is relatively lower because of the window effect.

Use the pull-down menu to select an instance of this VI.

reassigned? specifies whether to reassign the spectrogram by moving dispersed energy to the local center of gravity in the joint time-frequency domain. The reassignment can improve the readability of the spectrogram. The default is FALSE. | |||||||

extension specifies the method to use to pad data at the borders of the input signal to lessen discontinuity. The extension length is half the window length.
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signal specifies the input signal. | |||||||

time-frequency sampling info specifies the density to use to sample the signal in the joint time-frequency domain and defines the size of the resulting 2D time-frequency array.
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window info specifies the sliding window to use to compute the STFT and defines the resolution of the resulting time-frequency representation. Use the user defined window input to specify a customized window.
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error in describes error conditions that occur before this node runs. This input provides standard error in functionality. | |||||||

user defined window specifies the coefficients of the sliding window to use to compute the STFT. If you specify a value for user defined window, this VI ignores the settings in the window info input. Use window info to specify a commonly used sliding window, such as the hanning window or the hamming window.
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spectrogram returns the quadratic time-frequency representation of the signal. Each row corresponds to the instantaneous power spectrum at a certain time. Use the TFA Spectrogram Indicator to display the spectrogram on an intensity graph. You can save the time-dependent 2D array to a text file for use in another software environment. The resulting text file contains only Z values and does not retain the time axis information or the frequency axis information. You can use the TFA Get Time and Freq Scale Info VI to compute the time scale information and the frequency scale information of the time-frequency representation.
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scale info returns the time scale and the frequency scale information of the time-frequency representation, including the time offset, the time interval between every two contiguous rows, the frequency offset, and the frequency interval between every two contiguous columns of spectrogram. Use the TFA Get Time and Freq Scale Info VI to return detailed information about the time scale and the frequency scale. | |||||||

error out contains error information. This output provides standard error out functionality. |

reassigned? specifies whether to reassign the spectrogram by moving dispersed energy to the local center of gravity in the joint time-frequency domain. The reassignment can improve the readability of the spectrogram. The default is FALSE. | |||||||

extension specifies the method to use to pad data at the borders of the input signal to lessen discontinuity. The extension length is half the window length.
| |||||||

signal specifies the input signal. | |||||||

time-frequency sampling info specifies the density to use to sample the signal in the joint time-frequency domain and defines the size of the resulting 2D time-frequency array.
| |||||||

window info specifies the sliding window to use to compute the STFT and defines the resolution of the resulting time-frequency representation. Use the user defined window input to specify a customized window.
| |||||||

error in describes error conditions that occur before this node runs. This input provides standard error in functionality. | |||||||

user defined window specifies the coefficients of the sliding window to use to compute the STFT. If you specify a value for user defined window, this VI ignores the settings in the window info input. Use window info to specify a commonly used sliding window, such as the hanning window or the hamming window.
| |||||||

sampling rate specifies the sampling rate of signal in hertz. sampling rate must be greater than 0, or this VI sets sampling rate to 1 automatically. The default is 1. | |||||||

spectrogram returns the quadratic time-frequency representation of the signal. Each row corresponds to the instantaneous power spectrum at a certain time. Use the TFA Spectrogram Indicator to display the spectrogram on an intensity graph. You can save the time-dependent 2D array to a text file for use in another software environment. The resulting text file contains only Z values and does not retain the time axis information or the frequency axis information. You can use the TFA Get Time and Freq Scale Info VI to compute the time scale information and the frequency scale information of the time-frequency representation.
| |||||||

scale info returns the time scale and the frequency scale information of the time-frequency representation, including the time offset, the time interval between every two contiguous rows, the frequency offset, and the frequency interval between every two contiguous columns of spectrogram. Use the TFA Get Time and Freq Scale Info VI to return detailed information about the time scale and the frequency scale. | |||||||

error out contains error information. This output provides standard error out functionality. |

reassigned? specifies whether to reassign the spectrogram by moving dispersed energy to the local center of gravity in the joint time-frequency domain. The reassignment can improve the readability of the spectrogram. The default is FALSE. | |||||||

extension specifies the method to use to pad data at the borders of the input signal to lessen discontinuity. The extension length is half the window length.
| |||||||

signal specifies the input signal. | |||||||

time-frequency sampling info specifies the density to use to sample the signal in the joint time-frequency domain and defines the size of the resulting 2D time-frequency array.
| |||||||

window info specifies the sliding window to use to compute the STFT and defines the resolution of the resulting time-frequency representation. Use the user defined window input to specify a customized window.
| |||||||

error in describes error conditions that occur before this node runs. This input provides standard error in functionality. | |||||||

user defined window specifies the coefficients of the sliding window to use to compute the STFT. If you specify a value for user defined window, this VI ignores the settings in the window info input. Use window info to specify a commonly used sliding window, such as the hanning window or the hamming window.
| |||||||

sampling rate specifies the sampling rate of signal in hertz. sampling rate must be greater than 0, or this VI sets sampling rate to 1 automatically. The default is 1. | |||||||

spectrogram returns the quadratic time-frequency representation of the signal. Each row corresponds to the instantaneous power spectrum at a certain time. Use the TFA Spectrogram Indicator to display the spectrogram on an intensity graph. You can save the time-dependent 2D array to a text file for use in another software environment. The resulting text file contains only Z values and does not retain the time axis information or the frequency axis information. You can use the TFA Get Time and Freq Scale Info VI to compute the time scale information and the frequency scale information of the time-frequency representation.
| |||||||

scale info returns the time scale and the frequency scale information of the time-frequency representation, including the time offset, the time interval between every two contiguous rows, the frequency offset, and the frequency interval between every two contiguous columns of spectrogram. Use the TFA Get Time and Freq Scale Info VI to return detailed information about the time scale and the frequency scale. | |||||||

error out contains error information. This output provides standard error out functionality. |

The STFT spectrogram is the square of the magnitude of the resulting coefficients from the STFT. The STFT spectrogram is non-negative. All the values of the STFT spectrogram are positive. The other time-frequency representations, such as the Wigner-Ville Distribution, the Choi-Williams Distribution, the Cone-Shaped Distribution, and the Gabor spectrogram, can be negative.

Refer to the book Introduction to Time-Frequency and Wavelet Transforms for more information about reassignment.

Refer to the following VIs for examples of using the TFA STFT Spectrogram VI:

- Color Tables for Displaying the Spectrogram VI: labview\examples\Time Frequency Analysis\TFAGettingStarted
- Group Delay VI: labview\examples\Time Frequency Analysis\TFAFunctions
- Mean Instantaneous Frequency or Bandwidth (MIF or MIB) VI: labview\examples\Time Frequency Analysis\TFAFunctions
- Time-Frequency Resolution VI: labview\examples\Time Frequency Analysis\TFAGettingStarted

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