Phasing and phase correction
Doctor:I’ve recently become aware of phasing and attempts to correct it. It’s a bit tricky. An out of phase track or instrument really disappears when you listen to the final product.First of all, is it good to have some amount of phase differential in a song. It seems like phasing can add a bit of perceived depth to a track.
Also, can virtual instruments get out of phase? It seems they can. It also seems that an individual track can be in phase (when you meter it) but when you listen to that particular track or instrument in the final mix by soloing the track it can be less in phase. Why might that be?
As far as correcting the problem do you have any tips? I have Ozone3 which I like. T
It also has a phase meter and correction tools within the program. Those have been helpful.
Any explanations or tips are always appreciated.
On many mixers (software and hardware) and microphone pre-amps, you’ll often find a “polarity” switch, which is often mislabeled as a “phase” switch. In correct terms it is a polarity switch as it simply swaps the positive and negative. It would be the same thing as switching the positive and negative wires on your speakers… you aren’t really switching the “phase”, you are just switching polarity. However, if you flip the polarity of a signal and then add it back to the original version at an equal amount, you’ll get perfect cancellation. People often say that this is “out of phase” when more correctly the polarity is just reversed. Phase also relates to time, and a 180 degree phase shift would also imply a time shift and would not necessarily totally cancel out a signal if added back to the original signal, unless it was a steady state signal (such as a pure sine wave) that didn’t change in amplitude or frequency over time.
You mentioned that phasing can add a bit of perceived depth to a track…. well, yes… in a way. Many of those stereo widening type plug-ins basically use “phase” or polarity tricks to make audio seem wider. The most basic ones simply reverse the polarity of one of the two channels of a stereo signal and then add that back in at different amounts depending on how wide of an effect you want. The problem with those is that if you sum those two channels back to mono (such as on AM radio or a mono TV, or even FM radio where the reception is poor and the receiver switches to mono), then the signal that’s been widened with the simple polarity switch method will be greatly lowered in volume or even disappear completely, depending on how much of the reversed polarity signal was used. More advanced stereo widening tools will use other methods to make it more mono compatible.
You also ask if it’s good to have some amount of phase differential in a song. That question by itself really doesn’t make sense. What phase difference are you talking about? The phase difference between the left and right channel of a stereo mix? Or between a couple of different microphones used to record one instrument? Or using a stereo widening program on the whole mix?
Unless you pan every signal dead center in the mix, i.e., make every thing mono (no stereo signals), then you will always have a phase difference between the left and right channels of your stereo mix (if you are looking at a phase meter) by the simple fact that the two channels are different. If you want a nice sounding and wide stereo mix, you’ll typically pan different instruments to different sides of the stereo mix, or you may have some stereo signals that were recorded with two microphones, or that have stereo effects applied to them, or whatever. So, for a typical stereo mix, there is really no such thing as having the whole mix “in phase” or “out of phase”… the two channels are simply different. However, there will be some signals that will be mono, or mono to some degree, such as a dry vocal recorded with one microphone and panned right in the center, or the bass guitar, or kick and snare (if from a mono drum sample, or a single microphone without any overhead microphones or room microphones panned out). But, if your whole mix was mono, that would be pretty boring for someone listening in stereo and used to wide sounding stereo mixes.
Then, the next time you worry about phase is when you are mixing. Once you start doing a lot of EQ adjustments to tracks, then you are also messing with the phase of the signal. If it just a single track for an instrument, then it really doesn’t matter as much since that track isn’t being mixed in with another track of the same instrument, so there is nothing for it to have a phase difference with. Again, mixing a live drummer that was recorded with multiple microphones to multiple tracks is generally where you start to run into trouble… EQ or other processing on one track of the drum tracks can change the phase relationship of that track with regards to the other tracks, and you have to listen to how they all sound together, possibly even using that polarity reverse switch again to see which sounds best… or trying alternate types of EQs to see which one sounds the best.