What do "phase" errors sound like?

[Doug Young]

Hey Barry, a picture (I mean soundclip...) is worth a thousand words. Here's a quick demo for you. In general it's usually hard to "hear" phase, unless the issue is extreme. Better to check with tools (meters). And any stereo signal will have some phase differences - it's just the nature of stereo, tho you can have minimal-approaching-zero with coincident setups (XY or MS). Spaced pairs and ORTF have phase differences by design. The most obvious time you "hear" phase issues is when mixing two or more mics, like to mono, tho extreme cases can be recognized in stereo if you're used to listening for it.

Here's 4 short clips for you.



1) is spaced pairs, relatively in phase (as close as spaced pairs gets)
Here's what a correlation meter shows - not 100% in phase (the only way to get 100% is mono), but pretty well in phase for spaced pairs:

Stereo_in_phase.jpg

2) Same recording, but in mono. Notice the muddier sound. Because this is spaced pairs, the signals inherently have *some* phase differences at some frequencies (phase is frequency-dependent). So some frequencies reinforce each other when mixed together, others cancel out. Resulting sound is somewhat unpredictable, but this more muffled sound is typical of mixing a spaced pair recording to mono.

3) Now I'm playing games. I inverted one channel, simulating 180 degrees out of phase. Hear the unnaturally-wide sound? Once you hear this a few times, you can usually recognize it. Kind of makes your head spin. Some people discover this sound and like it at first, since it's kind of dramatic and ultra-wide. But it's not a good thing. Here's what the correlation meter shows for this:

stereo_phase_flipped.jpg

4) and finally, here's what this 180 out of phase example sounds like in mono. If the 2 signals were perfectly 180 out of phase at all frequencies, we'd have silence - total cancellation, but since the original signal was already partially out of phase and varied by frequency, flipping 180 still leaves some frequencies in phase. But the result is clearly much worse.

[TBman]

Originally Posted by Doug Young

Hey Barry, a picture (I mean soundclip...) is worth a thousand words. Here's a quick demo for you. In general it's usually hard to "hear" phase, unless the issue is extreme. Better to check with tools (meters). And any stereo signal will have some phase differences - it's just the nature of stereo, tho you can have minimal-approaching-zero with coincident setups (XY or MS). Spaced pairs and ORTF have phase differences by design. The most obvious time you "hear" phase issues is when mixing two or more mics, like to mono, tho extreme cases can be recognized in stereo if you're used to listening for it.

Here's 4 short clips for you.



1) is spaced pairs, relatively in phase (as close as spaced pairs gets)
Here's what a correlation meter shows - not 100% in phase (the only way to get 100% is mono), but pretty well in phase for spaced pairs:

Attachment 65654

2) Same recording, but in mono. Notice the muddier sound. Because this is spaced pairs, the signals inherently have *some* phase differences at some frequencies (phase is frequency-dependent). So some frequencies reinforce each other when mixed together, others cancel out. Resulting sound is somewhat unpredictable, but this more muffled sound is typical of mixing a spaced pair recording to mono.

3) Now I'm playing games. I inverted one channel, simulating 180 degrees out of phase. Hear the unnaturally-wide sound? Once you hear this a few times, you can usually recognize it. Kind of makes your head spin. Some people discover this sound and like it at first, since it's kind of dramatic and ultra-wide. But it's not a good thing. Here's what the correlation meter shows for this:

Attachment 65655

4) and finally, here's what this 180 out of phase example sounds like in mono. If the 2 signals were perfectly 180 out of phase at all frequencies, we'd have silence - total cancellation, but since the original signal was already partially out of phase and varied by frequency, flipping 180 still leaves some frequencies in phase. But the result is clearly much worse.

Thanks Doug!

[j3ffr0]

Originally Posted by Rudy4

If your stereo recording (with phasing issues) ever gets transmitted on an AM radio station you definitely don't want to be on the receiving end!

If I ever reach the point where there is outcry from my overlooked mono fanbase about how crap my recordings sound, I will know that I have arrived!


But I do always check my stuff with the correlation meter and make sure I'm in the green and make adjustments if not (thanks to a previous post of Doug's). While AM play is not very likely, I do want to make sure my stuff could be played on a single smart speaker and sound half decent at least.

[KevWind]

And just to clarify Barry are you were asking only about possible phase issues from two mics ? Because often it is a room reflection issue instead or as well..

But in simplistic terms the less obvious symptoms of either mics placements or room issues are the sound tends to be more 2D-ish than 3D-ish flatter and with less presence (air and spaciousness ) And it vary from obvious to subtle like say the difference between hanging a heavy blanket (between you and sound source) or like a cotton sheet

[Brent Hahn]

Originally Posted by j3ffr0

While AM play is not very likely, I do want to make sure my stuff could be played on a single smart speaker and sound half decent at least.

And if you make the kind of recordings where there are things to actually "mix," such as various instruments and especially a vocal, you may find that a balance you arrive at while listening in mono translates best to the real (stereo) world.

[shufflebeat]

This is quite an old vid but remains for me the best illustration of the problem of comb filtering, how it happens, how it changes with the environment and mic placement and, most importantly, what it sounds like.

Comb filtering is a specific type of phase mis-match problem but the mechanics and the characteristics of the audio distortion are common to all instances of phase mis-match.

https://youtu.be/4qgmY8jIGi0

The first half of the vid is most obviously informative to this thread.

[KevWind]

I posted this link in some other discussion on phase a while back But it's worth posting agin As I noted before Phase Errors can occur from using two mics on a single source , using two on multiple sources. OR it can come from room reflections creating comb filtering

If You scroll down to "What comb filtering sounds like " you get some pretty good examples

https://www.dpamicrophones.com/mic-u...ow-to-avoid-it

[Brent Hutto]

Originally Posted by KevWind

I posted this link in some other discussion on phase a while back But it's worth posting agin As I noted before Phase Errors can occur from using two mics on a single source , using two on multiple sources. OR it can come from room reflections creating comb filtering

There are some really funky artifacts you can get when using the microphones on an iPad that's sitting near a corner of the room to record a guitar. None of the mics actually point forward so the iPad firmware is combining a backward-facing mic with a side-facing one and the two microphones are each getting reflected sound from a different wall (on either side of the corner).

When playing single notes it doesn't sound quite right but not awful. But when you strum or play a chord there's this warble effect. I think that's related to comb filtering, the different frequencies of the various notes combined with the two microphones having different arrival times (one wall is closer than the other) it's just awful.