Question about phase reversal...

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IronFlippy said:
100% correct, listen to this guy. Please get out of the habit of saying "phase" reversal. It's polarity reversal, but manufacturers know that most people say phase, so rather than to confuse the majority of their customers, they purposely mis label it.

On a side note, playing with polarity reversal is fun! Pick a song, play it in mono with the polarity reversed on one of the channels. Anything center panned will get canceled out, leaving only the artificial reverb trails (or any other effects applied to it that were in stereo).
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Does it even make sense to "reverse" a phase? All you can do is shift a phase making it it lead or lag...



Stupid marketing making up concepts!! :mad::mad::mad:
 
vadoom said:
Does it even make sense to "reverse" a phase? All you can do is shift a phase making it it lead or lag...



Stupid marketing making up concepts!! :mad::mad::mad:
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No NO NO!

You guys are just wrong about this. Any common emitter amplifier circuit creates a phase inversion..... not a phase shift, not a polarity inversion...... a phase inversion. Phase, as in "what phase of the cycle is it in?" It's not a marketing mistake that engineers have accepted. The professors that teach electronics, that write the textbooks, didn't start calling it phase inversion or phase reversal because marketing people call it that. It is what it is. It is descriptive of the resultant action. That's why they call it that.
 
uh oh, another phase versus polarity battle!! :eek:

do a search. it's been covered a lot around here.

half the people argue that phase invert=polarity reverse
https://homerecording.com/bbs/showthread.php?t=200512

others argue that it's not the same
https://homerecording.com/bbs/showthread.php?t=229125

I'm in the middle now. Each argument is valid but we do worry too much about the semantics of it all. Everyone understands what you're talking about when mentioning phase or polarity switches. The science behind it all is pretty interesting though.
 
If I use Cubase to monitor levels in the mixer window of Cubase, If I hit the snare repeatedly and push the phase button (with monitor button highlighted ONLY, not record) would it reverse the polarity of the signal coming in? Or do I have to actually record a sound to be able to reverse it....if so that's gonna make my life a PITA....
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yes, you would be hearing the flipped sine wave by hitting the phase button in cubase, even before recording. we were just trying to make it clear that the track won't actually be recorded with the phase reversal, though...if you disengage the button after recording, it'll go back its "normal" polarity.
 
Ugh, here we go again....

Polarity inversion is a flipping of the signal around the 0 DC/centerline axis.

Phase inversion is a flipping of the waveform around itself.

The two are only the same - i.e have the same result - when there is waveform symmetry around the 0 DC centerline.

Any asymmetrical waveform (e.g. a snare hit) will be treated differently by true phase inversion than it will by true polarity inversion. Both will be "inverted" but the overall voltage envelope will be different.

See this post for a graphic illustration demonstrating an extreme example of the difference between phase and polarity..

G.
 
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Which am I, a Hatfield or a McCoy?

I tried to bite my tounge.....I really did. :D

I just can't, as an engineer, not respond to someone saying phase can only lead or lag, not invert.

Now Glen old buddy, I like your summation. Q - Is the phase switch on a balanced microphone properly or improperly named?
 
nice illustration there glen - it affirms my previous understanding that "phase reversal" is merely taking the existing waveform, and flipping it upside down, while also clearing up the difference between phase and polarity inversion
 
Robert D said:
Now Glen old buddy, I like your summation. Q - Is the phase switch on a balanced microphone properly or improperly named?
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Assuming that the switch is simply inverting the sign of the voltage (which is what I think the microphone is actually doing - correct me if I'm wrong there) I think the "proper" (so to speak) short answer is that it's truely a polarity inversion and not strictly JUST a phase inversion, because there is something more going on than if the phase were the only thing that was changing.

While the phase of the signal is also inverted, on an asymmetric waveform the values of the voltage envelope are also changing, which wouldn't happen on a pure phase shift only. The range of the envelope stays the same, but the actual values differ.

For a hypothetical example, let's say you're record a drum hit that, because of the actual action of the drum skin, peaks at (after preamping to normalize around 0VU) +16VU and -12VU. Flip the phase *only*, and those peaks remain the same with a DC offset on the waveform of +4VU. Flip the polarity, however, and ther is no DC offset, but the peaks now range from +12VU to -16VU. In both cases, the envelope range remains the same (28dB), but there is a DC offset of 4dB between the actual peak voltages between the two methods.

I think possibly (this is only a theory) that the reason that historically "phase inversion" and "polarity inversion" are semantically used interchangably, is because that's assuming a default symmetry around zero Volt reference. For example, when talking about an AC current, we're basically talking about a theoretical sine wave (not including noise) centered around a 0V reference. In such a case, there is no difference in result between a polarity inversion and a phase inversion; they quack the same. That default terminology has been inherited from basic electrical theory and is a basic concept that everybody pretty much understands.

The problem with that "understood" terminology comes in when we move into the world of audio and information theory where the desired waveforms are not simple symmetric waveforms. At that point, technically speaking, the equality between polarity and phase inversions starts to break down.

It's easy to just accept the intercahngability of the titles "phase inversion" and "polarity inversion", we all (including me) find ourselves using them interchangably all the time (the "Kleenex" effect). HOWEVER, when it comes to actually understanding and explaining the actual mechancs in forums like this one, the technical difference IS a real difference, and is important to understand in the long run.

The Qs I have, which I don't really know the answer to is, what do the various brands of digital software do when you click their inversion switches? Do they simply change the sign of the value, in which case they would truely be polarity inverters, and *technically speaking*, not just phase inverters? Or do they actually perform a time-independant (or instantaneous) phase shift or inversion, in which case they'd truely be phase inverters and not polarity inverters? I've never really looked at that in any kind of etail, so I'm not sure. It'd be easy enough to test on the various applictations, though.

G.
 
so is the reversal button on my DAW useless for getting more in phase on "asymmetrical waveforms" as my snare and such?
 
jrhager84 said:
so is the reversal button on my DAW useless for getting more in phase on "asymmetrical waveforms" as my snare and such?
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First of all, not all waveforms are perfectly symmetrical. My kick, for example, often looks as if it tends more towards one side of the zero crossing, but zooming in reveals no DC offset or other anomalies.

Second of all, I'm starting to wonder if this all may be related to latency, but I need more info. What are you recording, anyway? A drum kit? A full band? Multitrack? Exactly what issues are you having that makes you think phase cancellation is the root? I record my drum kit to 7 tracks, and often I'll have to align them to get rid of phase cancellation that occurs because the tracks aren't quite where they should be.

Just some food for thought....
 
I just have tons of mics, I use 8 on my kit right now, and It will be closer to 12 mid week (getting another interface to double mic snare and kick, and try room sound (I installed some treatment)... I really don't know if phase is a problem, but I don't know if it isn't either. I have no way of telling what the difference is, because it seems to me that the phase button doesn't do ANYTHING. I have one speaker off, and the other in mono...
 
jrhager84 said:
I just have tons of mics, I use 8 on my kit right now, and It will be closer to 12 mid week (getting another interface to double mic snare and kick, and try room sound (I installed some treatment)... I really don't know if phase is a problem, but I don't know if it isn't either. I have no way of telling what the difference is, because it seems to me that the phase button doesn't do ANYTHING. I have one speaker off, and the other in mono...
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Any way you can post some pics of your mic set-up?
 
jrhager84 said:
so is the reversal button on my DAW useless for getting more in phase on "asymmetrical waveforms" as my snare and such?
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Regardless of whether your wavefroms are symmetrical or not, a "Phase inverter" button could only work on two signals that happened to be 180° out of phase. If they happen to be, for example, 37° or 92° or 255° or anything else not even close to 180° out of phase, a simple phase inversion isn't going to help.

Phase or polarity inversion is mainly for use in instances such as when you're miking the snare from both the top and bottom. Because of the physical position, the soundwave each are picking up are automatically out of phase. This is because as you hit the drum skin, it is being pushed away from the top mic, but pushed towards the bottom mic. This sends the waveforms in opposite directions, which results in an inverted waveform. By switching the phase/polarity (whatever you want to call it ;)) on the bottom mic to be opposite of the top mic, you're now recording the waveforms more or less "in-phase" with each other.

But if your phase issues are because it takes slightly longer for the sound to bleed into the rack tom mic (for example), that's a time delay that's causing a phase shift, not a phase inversion, and neither a phase or a polarity inversion are going to help you much there. The best thing you can do there is to try to select mic models, mic positions, and gain levels that minimize the bleed and therefore minimize the phase interference from it.

G.
 
Robert D said:
No NO NO!

You guys are just wrong about this. Any common emitter amplifier circuit creates a phase inversion..... not a phase shift, not a polarity inversion...... a phase inversion. Phase, as in "what phase of the cycle is it in?" It's not a marketing mistake that engineers have accepted. The professors that teach electronics, that write the textbooks, didn't start calling it phase inversion or phase reversal because marketing people call it that. It is what it is. It is descriptive of the resultant action. That's why they call it that.
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Ok........... so............... say we take a waveform (sine for simplicity), and you inverse its phase, how would the sine wave look like?
 
Glen:

It makes sense now... I completely get it. I'll just invert the bottom snare mic and 2nd kick mic, and adjust from there.

MadAudio:

Here are my kickass Battery pics.....:rolleyes:

X/Y above my head
PIC00134.jpg


604's on toms:
PIC00135.jpg


609 on floor tom:
PIC00136.jpg


Another shot of the toms (hard to get a good angle)
PIC00137.jpg


All input is welcome. I can't wait until I upgrade to Battery 3.0 (better mics) :rolleyes::rolleyes::rolleyes:
 
vadoom said:
Ok........... so............... say we take a waveform (sine for simplicity), and you inverse its phase, how would the sine wave look like?
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Assuming it's a unity gain phase inversion in a perfectly linear circuit, properly biased.... starting at the very first positive excursion of the wave at the input, the antiphase signal at the output will simultaniously (no phase lag) begin the negative excursion. As the input reaches the positive peak of the first cycle, the output reaches the negative peak of the first cycle. It will continue to mirror perfectly as the waveform progresses. It doesn't matter what the waveform looks like, what the fundimental frequency is, or how complex it is (many frequencies and waveshapes combined), phase inversion happens outside the properties of time and applies equally to any and all waveforms.
 
In the strictest sense of the word, you really cannot "invert" phase, and you cannot have "phase inversion"... You can only have "phase shift", i.e. you can move the waveform a tiny bit forward or backward in time.

If people started to differentiate between polarity inversion and phase shift, this whole confusion would go away.
 
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