I've been learning about how to use phase cancelling to reveal vocals in a song using the original version combined with its instrumental. I've seen this done very well on YouTube. My problem is I have yet to succeed with this. I know this can be a very finnicky process and doesn't work with all songs. But why? That's all I've ever read, but no one actually stated the reason for it.
My actual problem, however, is that I can align the original song and its instrumental to the sample in Audacity and invert the instrumental, but I always get a constant phase offset as the song plays. Are the two versions that different? I don't understand why the waveforms wouldn't be aligned to the sample.
Is this a flaw with the song? Am I doing something wrong? Is this what everyone means by "it doesn't work with everything"? Some clarification would be helpful, as I'm still learning about general audio properties.
it doesn't work with everything.. plain and simple.. "phase cancellation" depends purely on how the original was recorded.. and all you will cancel are things which are out of the centre anyway.. hopefully leaving anything in the "middle" of the image intact.. but not always.. ANY phase shift between the paired channels will cancel everything there.. try it with a mono recording.. reverse the phase on one channel.. and end up with silence except for any crackles (if taken from a stereo signal source) .. This is most often used to make "klaraoke" tracks.. by dropping out the centre panned vocals.. but again.. not always.. some tracks will work, others not.. and anything with any phase shift between channels at all will give wild results. You didn't have control of the original recordings.. so if something doesn't work as expected it's out of your capabilities to do anything about.. because once recorded the signals are only one complex waveform, and to solve phase matters you need access to the pure multitrack master recordings... which if you had that obviously makes all this topic pointless.
look at it like this.. your ears are 2 separate signal sources for the brain.. they work on a combination of volume and phase to decide how loud and how close something is.. you can move a vocal track around from left to right in 2 ways.. by altering the volume of one channel.. or by delaying the phase slightly in one channel.. making that side seem "further away" even though the volume is exactly unchanged... this effectively "moves" the position of the source in the stereo "image" .. it's a subtle difference in method which achieves the same overall result... It was used a lot for the "mono remastered stereo" lp's of the mid and late 60's .. and those don't work if you try this method to strip or isolate vocals (or anything else in the "mix" for that matter) on them.. ever.
As to why some work and some don't.. I think it's obvious from the above.. anything that is not a pure acoustic precise phased stereo pair recording will have phase errors.. so using a cancellation method won't work as expected on anything but the pure right-left left-right which should leave the "in phase" centre information intact.. but as ears aren't that fussed about phase.. volume is the primary trigger for position, phase is very secondary (pro sound engineers train their brains to hear this subtle difference) in reality and some people just can't tell at all..
I can't think of any way to "solve" the not "broken" ones which don't work for you.. except with a hugely expensive piece of analog technology.. a realtime analog phase shifter with a steep cutoff passband parametric eq .. and even then.. all you do is succeed in shifting the phase of one channel.. defeating the object as the cancellation will fail..
You might do better using eq first to crop everything outside the vocal range.. say 200Hz to 4KHz.. then doing the opposite and adding the discarded "rest of it" back at a lower level.. then run your phase canceling stuff..
that's why some don't work.. it's complicated ;)
No doubt Mez will confirm all that sooner or later.. he's learning from me all the time ;) and I like to share my know how and skills with audio. I only spent 10 years as a professional live sound engineer.....
No, you haven't taught me that one yet. I have yet to find Crystal? sound cards yet. I tried a few select places that might hoard old treasures. None had them so I gave up. If they didn't have them no store would.
I am pretty much a lazy POS. The only time I get off my ass is to insure that I hear good clean HiFi sound. I would have REALLY like to have checked out a better fidelity audio capture. I just like to enjoy my music. I have enough challenges in my life not to make new ones.
I will say Paula X has as much in-depth audio knowledge as anyone on AD.
