Identifying phase problems with direct in and microphones

[rgraves]

Hi all,

I'm recording guitar tracks with both direct in and mic'd recording at the same time, and when I go in to make corrections under the extreme close up views I can see the two tracks don't match up very well. I mean everything sounds fine, but it just looks like the wave forms start at slighty different times.

My question is simply I don't understand how to identify a phase problem...can you just see it in the audio wave form, should the wave all match up, or is another progrsm needed to identify this?

Thanks

 

[bennychico11]

yes, you have phasing going on with your signal...however, this is not necessarily bad. Phase is a totally natural occurence with sound waves, it happens all the time. Phase gives us new and interesting sounds. Think about it, if the mic'ed guitar and the direct guitar where both in complete phase with each other and at equal amplitudes, you would just have the same sound on both channels...just louder. But you're recording two different things, so the periods of the waveforms aren't always going to line up perfectly....and that's okay.

But, when the phasing of the two tracks is so far off that it starts to make us cringe...that's when you have a problem. When the sound starts to swirl around and not sound like the original guitar we recorded, you need to investigate the problem. Believe me, you'll be able to hear that.
Move the file that's later in time (probably the mic signal) back in time so it lines up at a transient and listen to see if it sounds better. If it does, then you probably had a phase problem. If it doesn't or even sounds worse...then it was probably fine where it was. Phase problems usually are detected by ear first...then after that, to correct it I like to zoom way in and find out where the offending track is at.

Like I said, though....phasing isn't necessarily bad so don't worry if the tracks don't look lined up perfect enough. It takes a little delay in our signal before the human ear starts to hear a phasing problem...until that moment, the phasing going on with the track is actually helping the sound of the instrument sound the way we want it (because isn't that the whole reason you're mixing DI and mic together?). After we start to hear "bad phase" is when the ear starts to pick it up as a delay...and then you know you've gone too far.


HTH

 

[Farview]

Another quick way to tell if you have a problem:
1. pan both tracks center.
2. mute one of the track and listen
3. mute the other track(un-mute the first one) and listen
4. turn them both on. If the sound is stronger/louder, you don't have a phase problem. If the sound gets weaker/quieter, you have a problem.

 

[littledog]

As has been said - let your ears be the final determination, not your eyes.

But when looking at the two tracks you may notice that phase becomes a particularly bad problem when one track's waveforms are going up while the other one is going down, and visa versa. This means that there is a good chance some cancellation is going on. An example that may be even more out of phase may not sound nearly as bad, if in the second example the waveforms are at least moving up and down at the same time.

 

[bennychico11]

littledog's explanation on a "bad" phasing problem is right on. Generally speaking you'll see the cycle of one waveform go up while the other one is going down....this is when you'll hear something is up with the sound.

I posted an aural and visual explanation of phase here. The first page gets into a very technical discussion with cpl_crud, but page two is where I offered some examples.

of course use your ears, but there is no problem with using the eyes every once in awhile....especially if you don't have a ton of experience. A lot of us are visual beings and it's easier to see how things are done than to just hear it...it'd be like sitting in a class listening to the teacher about using a 96 channel Neve console. Wouldn't you rather be in front of one seeing how it all works? There has been years of work that has gone into metering and digital workstations to help with us with mixing, there's no harm in using those tools. Besides, the ears can lie to you every once in awhile