The Frequency Bands View in NoiseTools
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Let's have a look at the frequency band options available to us in NoiseTools. From the summary screen you can click the one third octave band spectra graph here or you can click the frequency bands button on the right hand side. Let's click the button.
This will open up the frequency bands view and depending on what instrument you've got this will determine what information is available to you on the screen.
If you got the B version of the Trojan Noise Nuisance Recorder you'll get both Octave and one-third octave band data. Here we're looking at the un-weighted Leq values values for each one-third octave band calculated across the entire measurement period. The highest band is shown highlighted red in the table. In this case 6.3 Hertz.
We can also select the 1:1 octave bands and again the highest values show on top of the table in red. We can also see the NR and NC values calculated for the 1:1 octave band data. Lets go back to the one third octave spectra. We can also go apply an A-weighting and a C-weighting correction to the data, this is shown on the graph.
Here we We can see the A weighting correction has been applied with some values higher than the original data due to the A weighting correction in these frequency bands.
Your sound level meter will be logging the one third octave band spectra throughout the measurement period.
In this example we got 42 hours of data so there's a lot of information available. If we select the time history button at the top of the screen, we'll initially see the overall spectra for the whole measurement period. The Markers Selection window, below the third octave-spectra, shows us the selection that we're looking at.
If we click the Play button the software we'll start to play back to us the spectra at a rate of one per second. You can see how the Spectrum changes over the measurement. We won't go through the entire 42 hour measurement but as the cursor passes an audio recording, this will played back as well and you can listen to it in relation to frequency data.
We'll stop the playback by clicking the STOP button. And we'll go back to view the entire measurement by dragging the selector window over. We can zoom into particular sections of data that are of interest to us. We've got a section of our data we've highlighted previously using the marker functions and we'll drag and zoom into this particular area.
We'll drag our mouse over This section, right click and select zoom. And again, drag that selection over, right click, and zoom.
So what we're looking at now is a small section of the overall time history highlighted by this marker, and represented on the time history graph.
And we're looking again at the one third octave spectra averaged over that small period. This can be quite useful in helping to identify low frequency noise or tonal noise sources in the data.
We'll use the mouse wheel to zoom out. And as we do so, the selection window will get larger and as we zoom further out audio recording will start to become visible.
We'll select an audio recording and the software will zoom into the one third octave data for that specific period. We can go even further into a particular period to locate particular noises. So we'll highlight on the graph Where the audio recording is, right click and zoom and the software will zoom in further and further into the data to give us more and more detail.
What we're looking at now is a one third octave spectrum for a very very short period of time, but we can see on the time history chart where this sits in relation to the overall measurement data
Again we'll use a mouse wheel to zoom out and as we do so more and more data is available and this is using the calculations the one third octave spectra.
Again we're looking at the unweighted one third octave spectra for the specified measurement Period. There are other ways of accessing the frequency information but we do it from the time history view. We'll jump back to the time history display and we'll select a particular part of the graph.
We'll drag over with our mouse and we'll right click and zoom. Again we'll highlight this section up even further, right click and zoom, and one more time until it fills the entire screen. Right click and zoom. Now we can right click on the graph, select go to frequency view, and the software will load the one third octave spectra for that highlight the section of our graph.
Again we're looking at unweighted 1/3 octave band brand spectra, let's jump back to the time history graph and zoom out with our mouse wheel and select another section of data.
Again zoom, Select the data, right-click and go to frequency view. We can see quite clearly here that there was a 12.5Hz one third octave band that's higher than its surroundings. So we may want to look at this in some detail. What we can do is jump back to the time history view, select the Channel window, select the 12.5 Hertz one third octave band time history and view this in relation to the other data.
But we can quite clearly see here that at some point in the graph, the 12.5Hz one third octave band data is significantly higher than its surroundings. So again this will be the cause of our high level in our third octave spectra
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