Would it be possible to get a visualizer like the THD bar graph, but showing 1/3 octave bars?
Hi @Westerdahl, it’s definitely possible. I think the idea of octave made sense a long time ago before DSP was really practical and the spectrum displays was implemented with analog filter banks. But with DSP, we can get much better clarity. What specifically are you thinking about?
Hi matt,
The standard that I am testing against requires to do the measurement in 1/3 octave bands for some of the tests.
IEC 60645-1:2017 eg. clause 5.7.2
BR, Westerdahl
Hi @Westerdahl, yes, I see your point as talk of octaves is rampant throughout the standards. Would it be suitable to have a visualizer that could report the energy in each band? You specify the octaves and start freq (eq 1 octave starting at 20 Hz) and then the energy in each span is reported as a bar graph? Currently it would be very hard to get on the main display.
Hi Matt,
Yes I can live with a visualizer as long it can show each band in dB’s.
Is it possible to use cursors on the visualizer?
BR, Westerdahl
Hi @Westerdahl, I think it will look a bit like below. You have the ability to specify channel, octaves per bin, the start freq, number of bins, and then the end freq is calculated for you. If you right click on the graph, you can display values of each bin. You can see the energy in the bin hovered over in this case -100.1 dBV.
This currently shows “Energy (dBV)” but that’s a bug and will be fixed. The correct Y axis is Amplitude (dBV). For example, the first bin is 20-40 Hz (one octave). If you make an RMS measurement set from 20 to 40 Hz, it will report the same number as shown in the bar.
Maybe it would be useful to have the level of each bar shown and have that turned on/off by the user. If you pick L+R and 1/3 octave, it’s a lot of bins and hard to make sense of the level of each bar. But if the user can enable/disable the option, it might be OK? What do you think?
Hi Matt,
Looks good.
It would be very nice if we could say lock to one bin eg. 1 kHz and then when you hover over another bin it will show the energy and the delta to the 1 kHz bin. In that way I do not think I need to have the energy for each bin.
BR, Westerdahl
OK, so maybe a checkbox to normalize the peak to 0 dB. That’s a good idea.
I would also find this display useful. I am being asked to replicate prior testing from a Klark Teknik DN60 Spectrum Analyzer / Pink Noise Generator, and I’ve tried explaining why swept-sine is better but we need to demonstrate equivalence to original testing first. I already procured a GoldLine PN2 stand-alone analog pink noise source, which obviously does not display “flat” on the standard QA403 output.
If I may, would it be better if the 1/3 octaves were labeled by their center frequencies?
Hi @joe, the spectrum visualizer is in the current release if you want to try it and report back with your source.
I’ll check about getting bin centers shown.
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Hi @Joe, yes, this will get re-worked to conform to ISO 266:1977 band centers. Thanks!
Hi @joe, what do you think about this? This takes the 1 kHz as the reference (instead of starting at 20 Hz).
Okay @matt, I’ve had some time to experiment with the 1.204 pre-release. I really appreciate the help!
However, like the original poster, I am interested in (30x) 1/3 octave bins. As you can see, the labels get a little too tight for legibility. So perhaps an auto-sizing or tilting the labels at an angle would be helpful.
Regarding your latest post about including the band centers, I think that display style could be along the right lines. However, the labels shown in the lower end don’t seem quite right per ISO-266:1997, for example the first band should have a center of 31.623 Hz and labeled as “31.5” whereas you have “31.25”. I understand how this comes about from the powers-of-two, but aligning with the spec would ease use of the graph for following historical test procedures.
As an aside, after updating QA40x I noticed when using the file->“save bitmap as” tool, it resizes the window to have a square shape. Is this configurable? I would prefer more like 4:3. Also the default file format in the visualizer saveas dialog is now .emf, where it previously was .png if I recall.
Yes, the ISO stuff for some reason is log10 based. How about something like this?
Once this is posted, would you mind spot checking a few bins with a tone to make sure the bin frequencies are breaking where you expect?
I noticed when using the file->“save bitmap as” tool, it resizes the window to have a square shape. Is this configurable?
The window gets resized such that the graph has the width specified in the menu item you selected. You can adjust the height. For example, here I did Edit->Copy Bitmap at 1200 wide, then reduced the height of the app window. That gives you more of a landscape.
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