Octave Analysis Express VI

Sound and Vibration Measurement Suite

Edition Date: June 2013

Part Number: 372416G-01

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Owning Palette: Frequency-Domain Measurements Express VIs

Requires: Sound and Vibration Measurement Suite

Performs fractional-octave analysis, including 1/1, 1/3, 1/6, 1/12, and 1/24 Octave for either a single channel or N channels. You also can apply A-, B-, or C-weighting to the octave spectrum.

The type of fractional-octave measurement you perform determines the number of filters to apply and the passband of those filters. You can use octave analysis to analyze audio and acoustic signals. These analyses exhibit characteristics similar to the response of the human ear.

A-weighting filters simulate the loudness of low-level tones and de-emphasizes frequencies below 500 Hz. B-weighting filters simulate the loudness of medium-level tones and are used infrequently. C-weighting filters simulate the sound of high-level tones and remove sounds outside the audio range of 20 Hz to 20 kHz

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Octave SpectrumDisplays the octave spectrum for a single channel or N channels.
Filter settledReturns TRUE when all octave filters are settled.
InputSpecifies if the measurement operates on a single channel or on N channels.
  • Input signal—Configures the measurement for a single channel or N channels. Changing this selection changes the data types of the input signals and computed measurements.
ConfigurationSpecifies the configuration settings.
  • Bandwidth—Specifies the bandwidth and has the following options:
    • 1 Octave
    • 1/3 Octave (Default)
    • 1/6 Octave
    • 1/12 Octave
    • 1/24 Octave
  • Weighting—Specifies one of the following weighting types to apply to the octave spectra:
    • Linear (Default)—Applies no weighting to the octave spectrum.
    • A Weighting—Applies A-weighting to the octave spectrum.
    • B Weighting—Applies B-weighting to the octave spectrum.
    • C Weighting—Applies C-weighting to the octave spectrum.
  • Frequency Range—Specifies the frequency range parameters for the octave analysis:
    • Frequency list—Allows you to select from a list of values.
    • Arbitrary values—Allows you to specify an arbitrary frequency range.
    • Low Frequency (Hz) Ring—Specifies the frequency of the lowest octave band. The default low frequency is 20 Hz. Only several discrete frequency values can be edited.
    • High Frequency (Hz) Ring—Specifies the frequency of the highest octave band. The default high frequency is 20k Hz. Only several discrete frequency values can be edited.
    • Low Frequency (Hz)—Specifies the frequency of the lowest octave band. The default low frequency is 20 Hz. You can set arbitrary frequency values in the range of Nyquist frequency.
    • High Frequency (Hz)—Specifies the frequency of the highest octave band. The default high frequency is 20k Hz. You can set arbitrary frequency values in the range of Nyquist frequency.
  • Total band power (dB)—Displays the total band power of the octave spectrum.
AveragingSpecifies the averaging parameters.
  • Averaging type—Specifies the averaging type.
    • Weighting mode—Specifies the weighting mode from the following options:
      • Linear—Applies equal weighting to all the data.
      • Exponential (Default)—Applies more weight to the most recent data.
      • Equal Confidence—Applies more weight to the most recent data, using a specific time constant for each band.
      • Peak—Maintains the peak level for each band.
  • Exponential Averaging—Specifies the exponential averaging parameters.
    • Response mode—Specifies the exponential averaging mode from the following options. This option is available only when you set Weighting mode to Exponential.
      • Slow—Uses a time constant of 1,000 ms. Slow averaging is useful for tracking the sound pressure levels of signals with sound pressure levels that vary slowly.
      • Fast (default)—Uses a time constant of 125 ms. Fast averaging is useful for tracking the sound pressure of signals with sound pressure levels that vary quickly.
      • Impulse—Uses a time constant of 35 ms if the signal is rising and 1,500 ms if the signal is falling. Impulse averaging is useful for tracking sudden increases in the sound pressure level and recording the increases so that you have a record of the changes.
      • Custom—Enables you to specify any strictly positive Time constant (s) suitable for your particular application.
    • Time constant (s)—Specifies the time constant, in seconds, for exponential averaging if you set Response mode to Custom.
  • Equal Confidence Averaging—Specifies the equal confidence averaging parameters.
    • Level (dB)—Specifies the confidence value in decibels to use if you set the Weighting mode to Equal confidence.

Block Diagram Inputs

ParameterDescription
input signalSpecifies the input signals.
error inDescribes error conditions that occur before this node runs.
restart averagingSpecifies whether to restart the selected averaging process. The default is FALSE. When you call this Express VI for the first time, the averaging process restarts automatically.

Block Diagram Outputs

ParameterDescription
octaveReturns the octave spectrum.
total band powerReturns the total band power in the octave spectrum.
unit labelReturns the unit label for the input signal.
error outContains error information. This output provides standard error out functionality.
filter settledReturns TRUE when all octave filters are settled.
octave infoReturns information about the octave spectrum.
Note  You must wire octave info when performing extended measurements. Do not modify the octave info values. If you want to view the information, you can right-click the octave info wire and select Custom Probe»Octave Info from the shortcut menu.

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