dolby decoding?

to bring files onto the machine, i pull the sd card from the little camera and copy 'em over. this works nicely, but the problem (once i get kdenlive to find my audio card) is that the camera won't let me switch off the two-channel dolby encoding, so the files come in encoded, which is to say compressed terribly and with a loud hiss.

is there a filter for kdenlive that decodes dolby-encoded audio? if not, has anyone come up with a way to do this before processing/editing/assembling the clips in kdenlive?

thanks very much.

If your file has more than one audio track, in the Clip Properties dialog, you can change the audio track to use.

thing is, there's no non-dolby-encoded track. dolby is a compression algorithm -- may be some equalization in there, too, but i believe it's mostly compression. this isn't compression in the digital sense, but in reduction of the dynamic range, with the range between the loudest and softest sounds reduced. the iea is noise reduction, but a non-decoded dolby trck is actually much noisier, because the floor hiss is amplified in the encoding. essentially the noise floor is raised -- a lot -- so while the track is dolby encoded the signal-to-noise ratio is just awful. it might be possible to "eardrum" it with an expander, but the right way is to use dolby's formula for decoding it.

hence my question. is there a plugin or filter or effect -- or even a free-standing application -- that will decode dolby-encoded tracks?

(actually, these tracks are kinda weird -- avidemux, for instance, doesn't recognize the audio format at all, which is puzzling.)

Ah thanks for that high level explanation, but I am confused... you keep writing "dolby encoded" but Dolby is a company with many technologies. If you can identify the technology, I would like to read more about it and see if some open source code already exists to integrate.

as far as i know, there's only one dolby stereo encoding. it's been around for a couple decades and is purely for noise reduction, not surround sound. it's employed in many inexpensive digital video recorders and is typically called dolby 2.0; also dolby digital and ac-3. it's encoded on recording and decoded on playback, but in that i'm not playing it back on the machine that encoded it, it doesn't get decoded -- hence, too bright a sound and a very noticeable hiss.

It sounds like the sox deemph effect might do what you want. See 'man sox' and search for deemph. You can test it out by extracting the audio from a clip and testing it with sox at the command line. If it works, then you can easily add a Kdenlive effect XML file to integrate it. I just did a test in MLT, and that effect requires the audio sample rate to be in 44100, but MLT tends to upsample everything to 48000. This frequency can be changed easily in Kdenlive Render's profiles, but not for playback in the UI. So, to integrate deemph fully into Kdenlive would require the addition of the MLT "resample" filter with a property "frequency" set to 44100.