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Tapping in Sonic Visualiser

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lacasse:
Hi Chris,

I was wondering if there were any development concerning the sunchronisation problems I experience when tapping in sonci visualiser?

Cheers
Serge

cannam:
Sorry for not replying sooner.  [Note to other readers: Serge sent me an email about substantial problems with the accuracy of the tapped timings when tapping in SV.]  To be honest, I don't really have an answer.

Tapping is implemented using a generic toolkit-level shortcut to a menu function, so it is very much at the mercy of the toolkit, windowing system, general system load, etc.  There is no real-time guarantee or system timestamping for tapping event delivery, or anything like that.  I don't understand why your results were so particularly bad, but even so I fear there may not be much that can be done within the constraints of your system to improve them, or at least I wouldn't know what.

Craig Sapp also did some measurements (on Windows -- I'm not sure whether you mentioned which platform you were using) of tapping performance and found that "long-term accuracy" was good but local quantization not so good (see http://www.charm.rhul.ac.uk/content/svtraining/svtour-20060630.ppt).  It's clear that he was seeing much better results than you are, although I consider the results he reports as "in need of improvement" as well.

To do substantially better than SV does currently, it may be necessary to bypass the GUI toolkit (Qt) for tapping events, but I'm not quite sure how best to approach that at present, at least in a cross-platform manner.

A more sophisticated and reliable method would be to use MIDI events for tapping.  Of course this would require a MIDI input device (e.g. cheap USB MIDI keyboard) but would have the advantage that MIDI library code is available on all platforms that is designed to handle rapid delivery with timestamping where appropriate.

Needless to say, patches are welcome!


Chris

lacasse:
thanks Chris,

I have tried many things and finally came with a (possible) solution. However, this means using another software for doing the actual tapping. One could use Audacity: however, there is always a delay (in my case around 250 ms), and we thus have to re-calculate all the data (with Excel for e.g.): long process.

My solution so far is to use Wavelab. Excellent sound editor, but very expensive. However, timing is perfect. In Wavelab we add markers on the spot by hitting the [insert] key. It's possible (in version 6) to export these markers directly into a txt file. Unfortunately, I only have version 5, and it exports the markers in a strange kind of file (in samples, not in ms, with a lot of extra anotations). One of my students has developed a short VB macro for adapting the Wavelab markers file into a one easy to read by SV (just the numbers). The results are perfect. I can even tap 16th notes (say at 120bpm) and they come out exactly as I played them. I don't know how Wavelab manages to have the markers perfectly in synch with the soundwave, but it works. If you're interested, I can send you the original WAV file, the Wavelab marker file, the transformed file (once compiled by the macro), the VB macro, and finally, the same WAV file tapped directly in SV and the same one tapped with Wavelab (and imported in SV).

Cheers
s

cannam:
Hm, that is a bit laborious!  I wonder whether there is anything else we could do.

Yes, if you wouldn't mind sending me those files, that might perhaps be helpful.

As a matter of interest, if SV did gain the ability to accept taps from a MIDI device, would you be in a position to take advantage of that?  Do you have a USB MIDI keyboard for example?  It would be a non-trivial addition, but might be worth doing if users would substantially benefit.


Chris

lacasse:
Dear Chris,

thanks for your reply. Yes, I use MIDI devices (M-Audio Ozosonic for ex.), so yes, it would be great. I'll send you all the files by email soon.

Cheers
Serge

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