4. How Octaves Are Calculated
Octaves are calculated using a series of time-domain based, band-pass filters.
Time data is fed into a series of narrow-band filters as shown in Figure 7. Each filter band represents the frequency range of each octave. In Simcenter Testlab, the filter shapes conform to the ANSI and IEC standards.
Both octave maps (like in the figure above) and octave sections can be calculated.
For example, Figure 8 below shows how the 12.5 Hz, 20.0 Hz, and 25.0 Hz octave bands change with time.
Depending on the application, an average level of the octave may also be calculated, rather than displaying it against time.
5. Calculating Octaves in Simcenter Testlab
In Time Data Processing, open the “Acquisition parameters” settings button (“Change Settings”) as shown in Figure 10.
Select an averaging method: exponential or linear. The exponential average weights the acquisitions taken later in time more heavily than earlier acquisitions. The linear average calculates the arithmetic mean of all the values.
Select a sound level type: fast (0.125 sec), slow (1.000 sec), impulse (0.035 sec), or user (custom). This parameter changes the length of the averaging frame. The averaging frame is the length of time that is used to calculate an average at every increment. Check out the Simcenter Testlab Throughput Processing Tips article for more information about increment and frames.
In Time Data Processing, open the “Section” settings button by clicking “Change Settings” under “Section. To calculate an octave map, go to the “Octave Maps” tab. Check on the octave band type that needs to be calculated as shown in Figure 11.
A result of this calculation would look something similar to Figure 12 below.
To calculate a single octave section, go to the “Octave Sections” tab. Type in the center frequency of the octave section(s) that is desired to be calculated as shown in Figure 13.
The octave section calculation will calculate how an octave behaves vs. a tracking parameter. Figure 14 below gives an example of the result from this calculation.
NOTE: There are a few additional tabs with the RTO (Real Time Octaves) suffix. Anything with the suffix RTO will used filter-based octaves to do processing. For example, “Psychoacoustic Metrics RTO” uses time-based filters to calculate sound metrics.
6. Octave Displays in Simcenter Testlab
Direct YouTube link: https://youtu.be/2FB1QOoPdeM
Octave data can be displayed using two different methods in Simcenter Testlab: the Octave Display and the FrontBack display:
6.1 Octave Display
There is a special display in Testlab called the “Octave Display". Data dropped into the display will always be shown in octaves.
The icon use to open the display is enlarged and shown in Figure 15 below.
The octave display automatically puts the x-axis in octave format. It also automatically puts data into a “block display” format (as octaves are traditionally displayed in).
When data is dropped into an octave display, it will look similar to Figure 16 below:
Figure: 16: Octave Display
Even a narrowband spectrum will be converted to octave format when dropped in the display.
6.2 FrontBack Display
If data is already in octave format, the FrontBack display can be used to display it as shown in Figure 17:
Figure 17: The FrontBack display can be used to display octaves and the corresponding narrowband spectrum overlaid.
To display octave data in the FrontBack display, here are some common settings:
With the FrontBack display, both narrowband and octave data can be overlaid. This can yield useful insights. For example, the exact frequency of a tone that is causing an octave band to be higher than the rest can be identified.
Questions? Email Scott MacDonald (firstname.lastname@example.org), contact Siemens Support Center, or reply to this article.