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You can use the Octave Extended Measurements VIs to perform the following measurements:

• Limit testing
• Octave weighting
• Octave band power value
• Octave subset
• Result table building

Weighting Filters

Use the SVT Weighting Filter (octave) VI to apply A-, B-, or C-weighting filters to a previously computed octave spectrum or spectra.

Octave Band Power Value

When you have a specific frequency band of interest in the octave spectrum and you want to measure the band power of the frequency band, you can use the SVT Get Octave Value VI. The SVT Get Octave Value VI returns the band power value of the octave spectrum for the specified input frequency band. If the input frequency does not exactly coincide with a nominal frequency, the VI finds the octave band that includes the input frequency. You can use the band power value that the SVT Get Octave Value VI returns to verify or perform limit testing on the power of that specified frequency band.

Octave Subset

If you have a range of frequency bands of interest and you want to analyze a subset of the octave spectrum, you can use the SVT Get Octave Subset VI. The SVT Get Octave Subset VI extracts the subset of the octave spectrum specified by a frequency range and limits subsequent spectrum operations to the frequency range of interest. This VI also computes the total band power of the returned frequency bands.

You can use the results that the SVT Get Octave Subset VI returns to compare how the total band power varies at different frequency ranges and to see the effect of a frequency range on the whole signal. You also can apply different weighting factors to different frequency ranges. Use the SVT Get Octave Subset VI in applications where you need to combine fractional octave bands, for example in loudness measurements.

The following example shows an application in which you divide the full octave spectrum into three different frequency ranges and determine the total band power for each range of frequencies. The following front panel shows the full octave spectrum and the three different frequency ranges.

Using the SVT Get Octave Subset VI, you can divide the octave spectrum into three ranges—low, middle, and high frequency ranges. The following block diagram defines the low range from 20 Hz to 200 Hz, the middle range from 200 Hz to 2000 Hz, and the high range from 2000 Hz to 20,000 HZ.

The total band powers indicator returns the band power value for each range of frequencies. The band power values for the low, middle, and high frequency ranges are 50.6 dB, 88.3 dB, and 49.1 dB, respectively. If you add the band power value for each range together, the result is the total band power value, 88.3 dB, for the full octave spectrum.

Octave Spectrum Conversion

Acoustic applications typically display octave graphs with the band powers in decibels. When displaying octave spectrum results for vibration measurements, you usually view the octave spectrum in a linear magnitude scale. The following block diagram shows an example of octave spectrum unit conversion.

The SVT Octave Spectrum Conversion VI converts the units of the weighted octave spectrum from power to magnitude.

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