Paul L wrote:Gale Andrews wrote:steve wrote:Videogamer555 wrote:I notice a problem in frequency selection in spectrogram in version 2.1.0. When you using the linear frequency display, for selecting the spectrum, it doesn't have the center frequency in the center. Instead it has it below the center.
That is correct. The spectral selection is a fixed order high, low or band pass filter, thus in the case of band pass the centre frequency is
proportionally in the centre, thus it will appear in the centre in Spectrogram (log f) view and below the centre in linear Spectrogram view. This is basic physics.
I certainly agree what "center frequency" means will need properly explaining in the Manual. We may wish to remember the likely skill/knowledge level of the majority of our users.
The question I have is what proportion and what centre are we talking about for the centre line in the Spectrogram views. Are we talking about centre frequencies of band* and notch filters? Anyone can see that the center frequency in either log or linear view for example between a range of 2000 to 8000 Hz is below what some might expect (5000 Hz). Neither is it the geometric mean which I understand would be 4000 Hz.
I guess many people will ask this, so I'll be first.
Gale
"Center frequency" meaning geometric mean is the usual technical jargon, is it not?
I am not a mathematician or physicist, like most users. I think many normal users may think centre of 2000 and 8000 Hz is 5000 Hz, like my mystery shoppers do.
The Manual did not say, but I "guessed" it was supposed to be geometric mean. But that is not where the spectrogram display puts the centre frequency.
Paul L wrote:If you select from 2000 Hz to 8000, surely 4000 should be the center. I just confirmed that this is so on my build, in log and linear views, and using the precise readouts of the spectral selection toolbar. If you don't see the same, there is a bug!
It looks like there is a bug sufficient to be confusing when you zoom in to the vertical scale in linear spectrogram view.
I wasn't using Spectral Selection Toolbar (most users won't because it is rightly off by default). However selecting upper and lower frequency limits by aligning with the ticks on the vertical scale I could see that the centre was not 4000 Hz.
So retesting selecting exactly 2000 and 8000 Hz in Spectral Selection Toolbar on Windows 8.1, I now see that the centre is indeed 4000 Hz according to that toolbar, but not in the spectrogram in linear view. The centre drifts above or below 4000 Hz according to the zoom level and position on the vertical scale.
- center_frequency.png (52.79 KiB) Viewed 1133 times
In Spectrogram log(f) view the vertical line seems to be much closer to or actually on 4000 Hz.
Also, the labelling on the vertical scale is not ideal. If I was not fully awake I might think I was selecting an upper frequency of about 8000 Hz here, but I am selecting about 7000 Hz.
- 7k_or_8k.png (15.42 KiB) Viewed 1133 times
And notice that where I have drawn the line for the upper frequency is above the 7000 Hz tick, but is actually below 7000 Hz according to the toolbar.
Gale
