Question about polarity/phase flip

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MoonSage
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Question about polarity/phase flip

Post by MoonSage » Thu Jun 06, 2019 3:39 am

Hi! Noob question here:

I was watching a friend work on a Pro Tools project and I noticed that when he zoomed in far enough to see the polarity of his tracks, when he flipped the phase you could actually see it in the waveform. But when I use the utility plug-in to flip phase in Ableton, I can hear a difference, but the waveform doesn’t seem to visually change. I guess it’s not a massive problem, but it’s a little annoying. I know I should trust my ears above all else but a little visual reinforcement helps me feel organized. Am I doing something wrong? Are my eyes playing tricks on me? Is there a way around this? Thanks a ton in advance for any help 😊

fishmonkey
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Re: Question about polarity/phase flip

Post by fishmonkey » Thu Jun 06, 2019 3:54 am

the Utility device inverts the polarity on the fly during playback, so the stored/displayed waveform doesn't change. if you recorded the signal post-Utility then that waveform would look different.

also, while we are on the subject, although the terms are often used interchangeably (and incorrectly), you can't really "flip the phase" of a signal, as phase is a time-dependent thing. you can shift the phase backwards and forwards in time, but you can't "flip it". flipping the polarity doesn't shift the signal in time, it flips the sign of the data, i.e. the negative parts of the waveform become positive, and vice-versa.
badbrainz wrote: I'm a drummer, so I'm already at an intellectual disadvantage here

MoonSage
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Re: Question about polarity/phase flip

Post by MoonSage » Thu Jun 06, 2019 6:48 am

fishmonkey wrote:
Thu Jun 06, 2019 3:54 am
the Utility device inverts the polarity on the fly during playback, so the stored/displayed waveform doesn't change. if you recorded the signal post-Utility then that waveform would look different.

also, while we are on the subject, although the terms are often used interchangeably (and incorrectly), you can't really "flip the phase" of a signal, as phase is a time-dependent thing. you can shift the phase backwards and forwards in time, but you can't "flip it". flipping the polarity doesn't shift the signal in time, it flips the sign of the data, i.e. the negative parts of the waveform become positive, and vice-versa.
Thank you for the insight!

I wasn’t really aware I could record post-utility. Is that something you could give me a rundown on or is it a more expansive topic to look deeper into? I didn’t really know I could apply stuff like that pre-Recording.

I also ran into the topic of destructive vs non-destructive editing while looking into this. I realize it’s a bigger topic I’ll need to study for a bit, but is there any advice you could give me on how to accomplish “destructive” polarity flip in Ableton? My google searching led me to all this stuff about resampling and freezing/flattening, which is going completely over my head at the moment but I’m sure I’ll figure it out over time. My computer is at my bandmate’s house an hour away from me so I only get to actually use Ableton and practice all this stuff when I’m there unfortunately

TLW
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Re: Question about polarity/phase flip

Post by TLW » Thu Jun 06, 2019 2:23 pm

If you really want to destructively change the phase (or anything else) on a track you can do it by putting utility on it, switching the phase change then resampling the track to another track or record the output of the flipped track to another track - just set the input on a new audio track to the track you want to record from, arm the new track's record button and record to it.

Or just put utility on the track, switch the phase and freeze the track using the "freeze" command from the right-click track menu. Freezing has the advantage you can un-freeze if you need to for any reason.

Though I'm not sure why you would want to do an irreversible ("destructive") phase change. A big advantage of DAWs over tape is that DAWs can edit audio without doing it destructively.
Live 10.1 Suite, M4L, 2014/15 MacBook Pro 15.3” Retina i7, OS Mojave 10.14.5. RME UFX, assorted synths, guitars and stuff.

MoonSage
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Re: Question about polarity/phase flip

Post by MoonSage » Thu Jun 06, 2019 2:38 pm

I think with almost all editing I would like to go a non-destructive route, but phase is just something in my mind where I would like to just deal with it and have my tracks in phase to where I could visually see it in the waveform and not have the utility or any plugins laying around cluttering things up. I’d rather just have all my phase issues dealt with and then clean it all up so it looks like I never had to do anything in the first place, and have this nice neat project with no phase issues before I really get started editing & mixing. Idk if any of that makes sense, it’s just how my brain works 😅 plus it must save some CPU usage right? And I can’t imagine why I’d really want to reverse my phase changes, assuming I got them right in the first place. It’s not so much like other edits or mixing where taste comes into play, its just “is my kick in phase with my overheads, yes or no?”

[jur]
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Re: Question about polarity/phase flip

Post by [jur] » Thu Jun 06, 2019 4:28 pm

Then, instead of using Utility or doing any destructive editing, you can simply offset your audio file a tiny bit so the waveforms of your 2 tracks are going in an opposite direction.
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MoonSage
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Re: Question about polarity/phase flip

Post by MoonSage » Thu Jun 06, 2019 7:48 pm

[jur] wrote:
Thu Jun 06, 2019 4:28 pm
Then, instead of using Utility or doing any destructive editing, you can simply offset your audio file a tiny bit so the waveforms of your 2 tracks are going in an opposite direction.
I’m kind of confused what you mean, and the point is to have them in the same direction

TLW
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Re: Question about polarity/phase flip

Post by TLW » Thu Jun 06, 2019 8:02 pm

MoonSage wrote:
Thu Jun 06, 2019 7:48 pm
I’m kind of confused what you mean, and the point is to have them in the same direction
Matching phase is about more than simply taking two wave forms and inverting one of them. Often that amount of phase change can still have enough issues to be a noticeable problem. Sometimes zooming in on a wave and moving it a tiny amount (as in milliseconds) until it better matches the wave you are trying to match phase with is a better solution.

There are plugins which can help a lot with phasing issues - I like Waves Inphase, but there are others, it’s just the one I’m most used to using - never pay full price for Waves plugins unless you need it urgently by the way, pretty much everything goes on sale sometimes.

As for the destructive editing, it may look “tidier” but there’s no assurance that e.g. changing the eq on the track won’t introduce new phasing issues that may need to be sorted out. Or things sound different if reverb is applies. Or lots of other things are done to the audio.
Live 10.1 Suite, M4L, 2014/15 MacBook Pro 15.3” Retina i7, OS Mojave 10.14.5. RME UFX, assorted synths, guitars and stuff.

fishmonkey
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Re: Question about polarity/phase flip

Post by fishmonkey » Thu Jun 06, 2019 10:35 pm

MoonSage wrote:
Thu Jun 06, 2019 7:48 pm
[jur] wrote:
Thu Jun 06, 2019 4:28 pm
Then, instead of using Utility or doing any destructive editing, you can simply offset your audio file a tiny bit so the waveforms of your 2 tracks are going in an opposite direction.
I’m kind of confused what you mean, and the point is to have them in the same direction
it's partly confusing because it seems that almost everybody confuses inverting the polarity of a signal with inverting the phase of a signal. as i said earlier, you don't/can't invert phase. even the Live user manual incorrectly talks about Utility inverting the phase, which is not what it does. Utility inverts the polarity of the signal.

if you have two audio signals, both shifting the phase or inverting the polarity of one signal will affect how those two signals add to and/or subtract from each other.

a classic example of a simple polarity issue is when recording a snare drum with two microphones, with one mic pointing down at the batter head, and the other pointing up at the snare head. when the snare drum is struck, the sound pressure wave is doing opposite things to the mic diaphragms: when one diaphragm is being pushed, the other is being pulled, and vice versa. in this situation you would usually flip the polarity on one of the mics on the mixing desk to minimise phase cancellation.

many phase cancellation issues are more subtle, however. for example, they can be caused by two microphones pointing in the same direction, but mounted at slightly different distances to the sound source. in this case, the sound reaches one mic slightly before the other (like with your kick and overhead mics). another example is comb filtering which occurs when two similar signals are slightly out of phase with each other. if you are lucky, these kind of phase cancellation issues can sometimes be improved by inverting the polarity. but other times shifting one or more of the tracks in time is required to get the sound you are after. as mentioned above, this can be done by shifting tracks in your DAW, or by using a plugin designed to tweak phase relationships between tracks.

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Last edited by fishmonkey on Thu Jun 06, 2019 10:47 pm, edited 4 times in total.
badbrainz wrote: I'm a drummer, so I'm already at an intellectual disadvantage here

[jur]
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Re: Question about polarity/phase flip

Post by [jur] » Thu Jun 06, 2019 10:36 pm

TLW wrote:
Thu Jun 06, 2019 8:02 pm
MoonSage wrote:
Thu Jun 06, 2019 7:48 pm
I’m kind of confused what you mean, and the point is to have them in the same direction
Matching phase is about more than simply taking two wave forms and inverting one of them. Often that amount of phase change can still have enough issues to be a noticeable problem. Sometimes zooming in on a wave and moving it a tiny amount (as in milliseconds) until it better matches the wave you are trying to match phase with is a better solution.

There are plugins which can help a lot with phasing issues - I like Waves Inphase, but there are others, it’s just the one I’m most used to using - never pay full price for Waves plugins unless you need it urgently by the way, pretty much everything goes on sale sometimes.

As for the destructive editing, it may look “tidier” but there’s no assurance that e.g. changing the eq on the track won’t introduce new phasing issues that may need to be sorted out. Or things sound different if reverb is applies. Or lots of other things are done to the audio.
Yeah sure, but here MoonSage is talking about "kick being or not in phase with the overheads". So I suppose (s)he has to deal with a drum kit recording and in this situation it's perfectly fine to slightly delay tracks and actually sometimes even makes more sense than pressing a phase-flip button...
But I have the feeling that MoonSage is fiddling with something that doesn't make total sense yet for him/her... and if I'm right then the real answer is learn what is phase and what you are doing because it's not the really in the "Mixing 101" ballpark... and forget about that shiny trick your friend show you until then.
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fishmonkey
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Re: Question about polarity/phase flip

Post by fishmonkey » Thu Jun 06, 2019 10:36 pm

whoops! double-post redacted!
badbrainz wrote: I'm a drummer, so I'm already at an intellectual disadvantage here

Fanu
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Re: Question about polarity/phase flip

Post by Fanu » Fri Jun 07, 2019 6:17 am

fishmonkey wrote:
Thu Jun 06, 2019 3:54 am
also, while we are on the subject, although the terms are often used interchangeably (and incorrectly), you can't really "flip the phase" of a signal
I raised some convo on this on the beta forum: Utility says it gives you control over "phase" of each channel, and I suggested that be changed to "polarity" to promote correct terminology…it's still wrong though.
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MoonSage
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Re: Question about polarity/phase flip

Post by MoonSage » Fri Jun 07, 2019 12:48 pm

[jur] wrote:
Thu Jun 06, 2019 10:36 pm
TLW wrote:
Thu Jun 06, 2019 8:02 pm
MoonSage wrote:
Thu Jun 06, 2019 7:48 pm
I’m kind of confused what you mean, and the point is to have them in the same direction
Matching phase is about more than simply taking two wave forms and inverting one of them. Often that amount of phase change can still have enough issues to be a noticeable problem. Sometimes zooming in on a wave and moving it a tiny amount (as in milliseconds) until it better matches the wave you are trying to match phase with is a better solution.

There are plugins which can help a lot with phasing issues - I like Waves Inphase, but there are others, it’s just the one I’m most used to using - never pay full price for Waves plugins unless you need it urgently by the way, pretty much everything goes on sale sometimes.

As for the destructive editing, it may look “tidier” but there’s no assurance that e.g. changing the eq on the track won’t introduce new phasing issues that may need to be sorted out. Or things sound different if reverb is applies. Or lots of other things are done to the audio.
Yeah sure, but here MoonSage is talking about "kick being or not in phase with the overheads". So I suppose (s)he has to deal with a drum kit recording and in this situation it's perfectly fine to slightly delay tracks and actually sometimes even makes more sense than pressing a phase-flip button...
But I have the feeling that MoonSage is fiddling with something that doesn't make total sense yet for him/her... and if I'm right then the real answer is learn what is phase and what you are doing because it's not the really in the "Mixing 101" ballpark... and forget about that shiny trick your friend show you until then.
I'm pretty aware (I think...) of the differences between phase and polarity, I just keep using the word phase and causing more confusion lol. I completely mean to be talking about polarity, sorry for the confusion. As for phase I hope that I can prevent the vast majority of phase issues just by good mic placement. I have read about how a lot of people move their transients around so that (for example) the snare in the close mic and the snare in the overheads hit at the exact same time, and I've been told it's "punchier" that way, but I've also heard the advantages of NOT doing that, and letting their be that very tiny time distance between the close mic and the overhead, aiding in the impression of the space that the drum kit inhabits. I will probably experiment with both of these methods and also be using a phase plug-in. But my first concern is just polarity. Particularly, I want to make sure my kick drum transients are positive and that the other mics picking it up match. But maybe I'm being naïve and missing the role that actual phase plays here? Like should I be working on both phase and polarity simultaneously, due to their relationship to each other? Or am I right to just flip polarities as necessary first, and then worry about phase/scoot the tracks around/use a phase plug-in etc?
Btw when my friend flipped polarity on a track, it wasn't a "shiny trick" as much as I just happened to be watching him work in Pro Tools and notice it lol. It seemed pretty mundane but it just feels odd when I flip polarity in Ableton and don't physically see it, zoom in and the waveforms of two tracks are still visually opposite of each other...you've all made plenty fair enough points as to why I shouldn't be bothered by it, but it just does bother my eyes for some reason xD I guess I don't have to lose hair over it though.

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