Spectrogram display

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Moderator: Derek

Spectrogram display

Postby h4yn0nnym0u5e » Sat Oct 20, 2007 10:44 pm

Hi Derek

Just got back to using Wave Corrector after a bit of a gap, on a shiny new computer (woo hoo! On re-installing, I also discovered I first registered in April 2000...)

Anyway, to the point. Where WC fails to spot a click, but I can hear it, I found a trusty copy of Cool Edit 96 would often show it very clearly in its "Spectral" display. This is AKA a spectrogram, you probably know all about them but for the interested forum viewer, you can see an example here: http://en.wikipedia.org/wiki/Image:Spectrogram_of_violin.png . I find a click very often shows up as a narrow wide-frequency (i.e. bright from top to bottom) feature, only masked if there's a lot of other wide-frequency stuff happening at that precise instant.

As you obviously have the FFT code in there already, I wonder if it would be possible to add a spectrogram display option. In CE96 it replaces the waveform view, which works well - you simply centre the click in spectrogram mode, switch to waveform and zoom in a bit. Care is needed, as the spectral display is usually about 20ms wide, whereas the click is of course often only a few samples.

Hope this sounds useful and easy to do!

Best regards

Jonathan
h4yn0nnym0u5e
 
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Joined: Sat Oct 20, 2007 9:50 pm

Postby Derek » Mon Oct 22, 2007 7:22 am

Hi Jonathan

Yes, this is a good suggestion. Thanks for making it.

There is already a 'spectrum view' in Wave Corrector (selected via the View menu). This shows the spectrum of a small section from the centre of the main window. If you're trying to track down the click, you can scroll the main window and observe the changes to the spectrum. When you're centred on the click, the spectrum normally becomes flatter and higher.

Although this is a reasonable technique, I think your spectrogram suggestion would be a very useful additional option and I'll try to incorporate it in the next release.

To finish on a note of caution however, I have found in practice that this technique of identifying clicks is normally only effective with the relatively severe ones. And in these cases, they are nearly always detected automatically anyway. So, the technique may be of limited value.

best regards
Derek Higgins
Wave Corrector Developer
http://www.wavecor.co.uk
Derek
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Location: Coleshill, United Kingdom

Postby h4yn0nnym0u5e » Mon Oct 22, 2007 9:33 pm

Hi Derek

Thanks for taking my suggestion on board. I did indeed note the spectrum view, but didn't really find it as helpful as the spectrogram - the eye can pick out a vertical bar of colour very quickly indeed, far faster than it can spot a flicker of the spectrum as it goes flatter.

Historically I've probably tended to be a bit conservative on my click threshold settings, so it's likely I've manually corrected quite a few that Wave Corrector could have done either automatically or by a subsequent super scan. Some of that's native caution, and some down to original source material which has wanted sounds that look like clicks to Wave Corrector!

One thing I did find useful was to be able to adjust the "gain" on the spectrogram, especially if it's using a "false colour" display - when set right, the transition from, say, blue to magenta is quite striking.

best regards

Jonathan
h4yn0nnym0u5e
 
Posts: 5
Joined: Sat Oct 20, 2007 9:50 pm

Postby Derek » Tue Oct 23, 2007 1:32 pm

Hi again

Yes, I can see the advantages of the spectrogram display and I look forward to coding it. And yes, I'll try to include a gain control of some sort.

I'll let you know when a beta is available as you may be able to give me some tips.

all the best
Derek Higgins
Wave Corrector Developer
http://www.wavecor.co.uk
Derek
Site Admin
 
Posts: 476
Joined: Sat Jan 01, 2005 7:57 pm
Location: Coleshill, United Kingdom


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