Is this something you're finding on a lot of soundtracks or just the odd few?

Well admittedly I haven't decoded enough to qualify as a "lot" or even have statistical significance. But let's say that out of 10 tracks I did, I saw it in 3 or 4. It might be coincidence, but a strange one for sure, especially since it was from different sources too - 35mm capture, 35mm capture from another scanner, LD. And then I found that article about some guy saying he noticed the same (linked in OP). Seemed like a pattern to me.

Out of curiosity, how much difference in dB we are talking about?

What I've seen seems to be around 3 dB, but I've seen one with closer to 1 dB as well. The way I "measured" it was to find a few places with dialogue (which should be centered) and adjusting one channel's volume until the decoded left and right waveforms were roughly the same size.

Wow, 3dB means it sounds twice as loud!

Actually twice as loud is 6 dB I believe.

From the web:

Quote:A 3 dB change yields a 100% increase in sound energy and just over a 23% increase in loudness.

Quote:Sound studies tell us time and again that a 3dBA increase in sound level is barely noticeable to the human ear. In fact, you have to raise a sound level by 5dBA before most listeners report a noticeable or significant change. Further, it takes a 10dBA increase before the average listener hears “double the sound”.

Interesting. Well what I meant (or thought I meant) by twice as loud is that the amplitude of the audio waveform roughly doubles at 6 dB. Of course the human ear doesn't react linearly to that, same as it doesn't with light.

When you start getting up to reference playback levels then +3dB is quite a lot

The other question is if 3dB difference in a stereo panorama are noticeable.

I could hear the difference on headphones pretty clearly, that's how I became aware of it the first time I think. But on normal loudspeakers there is too much crosstalk for me to still hear it, or at least I'd have to train myself to hear it probably. Since some of the left channel reaches your right ear and vice versa, so the differences are further minimized compared to headphone usage.