Absolute Polarity in Mastering

[turtlerock]

as bob k discussed way up the top , lots of "pro gear "has not settled itself on absolute polarity (lipinski..? apparently as well) standards !

what i have done here is align our systems is using a emt phase gun as the master reference , we have made sure every single thing in our studios "pushes" as its first wave front impulse .

i am sure there are other products but the emt , has a speaker / microphone as well as an xlr send and receive system , it sends a little ramped click throughout the system and then checks that is received as it was sent .

i think about 1/3 of our gear was not absolute phase positive , so i figure it is something that while clearly still in dispute even as an audable concept , was worth sorting out .

is it a mastering issue? .. well if its an audio issue , its a mastering issue.
but who will hear it if you dont fix up a track with obvious issues ...?
just you .. but thats ok thats why we do this right ..?

[UnderTow]

Originally Posted by philip

yes of course! if there was a standard about polarity* it would be the first thing to check. I'm not reasoning if it's wrong or not, I just say it does not have any practical meaning today.

Of course there is a standard. Imagine a studio where all the mics and preamps etc are wired up correctly. A positive wave front causes a positive voltage. All the other gear in the studio is also wired up correctly and all the way through the mix those original positive wave fronts cause positive voltages etc. Then the last piece of equipment in the chain used to bounce the mix has the wiring mixed up. Hey! Suddenly the polarity of the mix has been inverted.

No one notices this until it gets to the mastering session. The ME finds the mix a bit lackluster and lacking punch, tries flipping the polarity and presto!, the punch is there. There was a polarity issue and the ME resolved it.

Of course gear can introduce phase shifts but AFAIK it is unusual for a piece of equipment to cause the positive wavefront of say a kick drum to become negative (assuming the wiring is correct).

Lagerfeldt, what do you use to check and correct the polarity of mixes? Are you doing this in the analogue or digital domain?

Alistair

[philip]

some more info on the subject, taken from Phase, Time and Distortion in Loudspeakers
I do not answer for this articel but I find it useful.


Phase Audibility
The audibility of absolute phase is nil.

I must explain this further, as this is a somewhat contentious issue. It can be proven in ABX tests that there are some signals where the difference between a non-inverted and inverted signal is audible. Certain waveforms and instruments are highly asymmetrical, and if listened to in isolation will sound different if the phase is reversed. The difference is not subtle, either - it can be very pronounced. This is much more likely to be a result of loudspeaker driver behaviour than anything else, and the "correct" phase is anyone's guess - should it be inverted or not? We don't know the answer, since we will be unsure of what the instrument sounded like "live" - it is possible that neither the inverted or non-inverted recorded signal will sound like the original, so the point is moot.

The key issue here is that if we listen to a saxophone (a good example of an asymmetrical waveform) with the phase normal then reversed, all we hear is a difference - there is not necessarily a "right" or "wrong" phase, since it depends on the way the instrument was miked in the first place. If the period between listenings is extended to a few minutes, the chance of us hearing the difference will be minimal, and we still won't know which is "right" and which is "wrong" - all that this proves is that there is a difference, and it only becomes audible with some instruments.

This is probably the only case where an ABX test proves something that is not relevant in the general sense - so yes, absolute phase can be audible, but it is (generally) irrelevant. While it may be possible to pick a difference, it is only a difference - neither sounds better than the other.

[pmx]

i dont wish to sound like a wiseguy here, but isnt 'overall polarity' not a better way of describing it?

asl, the theatre intercom guys, make a device such as the emt, very usefull in big speaker systems like line arrays. i must say though: i've never a difference in live sound systems with one absolute polarity or the other way around. in fact, i've got some kt eqs over here right now that a pin3=hot, and no difference. i think if there is a audible difference, a high resolution speaker is still the only way of hearing it with: all other typical speaker problems are a bigger influence imo...

when i get back to the studio i'll check my lipinski's, thanks for mentioning it bob...

[Bob Olhsson]

Originally Posted by philip

I must explain this further, as this is a somewhat contentious issue. difference, it is only a difference - neither sounds better than the other.

It is only contentious among people who haven't done their homework. It was established as fact by both RCA and Bell Labs in the 1930s.

[philip]

Originally Posted by Bob Olhsson

It is only contentious among people who haven't done their homework. It was established as fact by both RCA and Bell Labs in the 1930s.

Thats great Bob, let me know how to do that. (find the "right" polarity in a usefull way)

I don't want to sound harsh, I allways respect your opionion, but this time you are wrong, read the whole article instead of makeing false quotes.

[Bookerv12]

Originally Posted by philip

Thats great Bob, let me know how to do that. (find the "right" polarity in a usefull way)

I don't want to sound harsh, I allways respect your opionion, but this time you are wrong, read the whole article instead of makeing false quotes.

Um,
I see interesting thread titles and find myself skimming through the now usual 90% arrogant, clueless contributers... and actually sit and read thoughtful, helpful answers... interestingly enough, usually posted by guys named Bob.
Hey young guys:
Sit and think before you actually respond in a negative way to a guy who is taking his valuable time to help you. Especially a guy who has forgotten more than you will ever know.
I have yet to see one of you internet heroes confront someone in a rude way to their face.

[philip]

Originally Posted by Bookerv12

Um,
I see interesting thread titles and find myself skimming through the now usual 90% arrogant, clueless contributers... and actually sit and read thoughtful, helpful answers... interestingly enough, usually posted by guys named Bob.
Hey young guys:
Sit and think before you actually respond in a negative way to a guy who is taking his valuable time to help you. Especially a guy who has forgotten more than you will ever know.
I have yet to see one of you internet heroes confront someone in a rude way to their face.

Yes you are really contributing yourself.

Please prove your point (all of you who disagree with me) in a valid science way and I will stop contributing myself.

But because you are not going to be able to do this you will probably just continue calling me clueless - that sooo much easier than actually learn something.

[Bookerv12]

Originally Posted by philip

Yes you are really contributing yourself.

Please prove your point (all of you who disagree with me) in a valid science way and I will stop contributing myself.

But because you are not going to be able to do this you will probably just continue calling me clueless - that sooo much easier than actually learn something.

"A valid science way"??
Clueless would be quite a step up...
You're a moron.

[philip]

Originally Posted by Bookerv12

"A valid science way"??
Clueless would be quite a step up...
You're a moron.

Thanks for the info on absolute polarity, really helps.

as I said...


But because you are not going to be able to do this you will probably just continue calling me clueless - that sooo much easier than actually learn something.

[UnderTow]

Originally Posted by Lagerfeldt

Maybe I should provide an audio example so everybody can judge for themselves?

Here is a kick & saw bass with a polarity reversal half way through: http://puretone.nl/Polarity.wav

Alistair

[kategra84]

Originally Posted by UnderTow

Here is a kick & saw bass with a polarity reversal half way through: http://puretone.nl/Polarity.wav

Alistair

i am total beginer and i hear no diference in the hole polarity.wav
i listen to this at work , on crapy consumer headfones

[kategra84]

Originally Posted by kategra84

i am total beginer and i hear no diference in the hole polarity.wav
i listen to this at work , on crapy consumer headfones

and correct me if i am wrong - but audio signal is AC, so it's polarity changes many times every second, so polarity at 20 hz changes 20 times per second. So how can you change polarity in a persistent way ???? maybe you can change the phase, but polarity is bounded to frequency

[Nordenstam]

Sound is not only steady state, there's impulsive action too!

A picture of the bass drum in the wave file Alistair posted:

[kjg]

Originally Posted by UnderTow

Here is a kick & saw bass with a polarity reversal half way through: http://puretone.nl/Polarity.wav

Alistair

I hear the difference pretty clearly on my macbook pro, but only on the kick since the speakers reproduce pretty much nothing under 200 Hz. It is just less punchy. On decent headphones the bass line seems less defined as well.

I think tracking and mixing engineers should be very aware of absolute polarity, particularly on parts with strong transients, as it can make a substantial difference. In multimic situations, the best compromise is their subjective call (although it often pretty obvious and really not that subjective at all what is best). In purist recording situations their obviously *is* a correct polarity.
The mastering engineer should have no net polarity inversions throughout his chain as to not mess up decisions made earlier in the production process.
I can imagine the odd case where the ME should correct for accidental polarity inversion though.

[kategra84]

Absolute polarity = phase ?

"Two oscillators that have the same frequency and different phases have a phase difference, and the oscillators are said to be out of phase with each other. The amount by which such oscillators are out of step with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π. If the phase difference is 180 degrees (π radians), then the two oscillators are said to be in antiphase. If two interacting waves meet at a point where they are in antiphase, then destructive interference will occur. It is common for waves of electromagnetic (light, RF), acoustic (sound) or other energy to become superposed in their transmission medium. When that happens, the phase difference determines whether they reinforce or weaken each other. Complete cancellation is possible for waves with equal amplitudes." wikipedia - phase

[UnderTow]

Originally Posted by kategra84

Absolute polarity = phase ?

"Two oscillators that have the same frequency and different phases have a phase difference, and the oscillators are said to be out of phase with each other. The amount by which such oscillators are out of step with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π. If the phase difference is 180 degrees (π radians), then the two oscillators are said to be in antiphase. If two interacting waves meet at a point where they are in antiphase, then destructive interference will occur. It is common for waves of electromagnetic (light, RF), acoustic (sound) or other energy to become superposed in their transmission medium. When that happens, the phase difference determines whether they reinforce or weaken each other. Complete cancellation is possible for waves with equal amplitudes." wikipedia - phase

I like that Wikipedia article because it clearly says "antiphase" rather than "polarity". Polarity inversion happens when you switch two wires (or the equivalent in the digital domain). Many analogue (and digital) consoles have polarity switches on every channel. Those are not phase switches because the timing is not affected.

Phase is a time thing. If you slide one waveform on a time line by half an oscilation cycle, you have rotated the phase by 180°. You have not changed the absolute polarity.

Alistair

[kategra84]

Originally Posted by UnderTow

I like that Wikipedia article because it clearly says "antiphase" rather than "polarity". Polarity inversion happens when you switch two wires (or the equivalent in the digital domain). Many analogue (and digital) consoles have polarity switches on every channel. Those are not phase switches because the timing is not affected.

Phase is a time thing. If you slide one waveform on a time line by half an oscilation cycle, you have rotated the phase by 180°. You have not changed the absolute polarity.

Alistair

i bet if you mix the two signals in the Polarity.wav or in the Picture above they will cancel out just as two phases of the same signal at 180°. If absolute polarity is not phase, and not mesured in degrees, than how can you mesure it ?


ps - when i'll get home i'll mix the tow signal to see what happens

[clarkjohnsen]

Philip wrote: Let me know how to do that (find the "right" polarity in a useful way).

Let me, a newbie, jump into the ring. My attention was drawn to this discussion by a friend who knows of my abiding interest in the topic. Let me first introduce myself as author of a book called The Wood Effect: Unaccounted Contributor to Error and Confusion in Acoustics and Audio. And I certainly do see a lot of confusion here! Perhaps to start, a definition of terms would help. The abstract to The Wood Effect puts it this way:

"Masked by random combination with other distortions in the music reproduction chain, an unsuspected major contributor has lain hidden: Aural sensitivity to ‘phase inversion’ — the Wood Effect.

"Musical instruments normally create compression wavefronts. Electronics, however, often invert that natural, positive polarity to unnatural, negative rarefaction, thus diminishing physical and aesthetic impact. The term Absolute Polarity uniquely describes the correct arrival to the ear of wavefronts from loudspeakers, with respect to actual musical instruments.

"Wrong polarity, when isolated, is obvious to all. Its present neglect results from habitual disregard for phase response, especially in loudspeakers."

Yes, loudspeakers – those nasty incoherencers with high-order crossovers -- mask polarity with hundreds of degrees of phase distortion. No wonder people question the idea of a mere 180 degrees being audible. But audible it is, on a minimum-phase system.

That assumes, however, that the recorded material is not itself phase-gemischt. In pop music one cannot trust the source to be phase coherent, but take any minimally-miced recording -- or even better a true monaural recording -- and the phenomenon will leap out at you... anyway on a minimum-phase loudspeaker.

Considerable confusion arises from not distinguishing between "absolute polarity" and simple "polarity". In most instances the latter term is correct. Equipment (electronics, mics, speakers) possesses only "polarity" -- and that means either "inverting" or "non-inverting". Whichever way a signal is inscribed onto a disc or committed to tape (and note well, there are no effective standards for any of this), it still retains all other audio properties. Whatever the reproducer's native polarity (and it could go either way), the recording may still be heard entirely properly, if correction, if needed, be made.

The question arises, how may this problem be accounted for in mastering? Answer: Not easily! Material has been created in environments where no consideration for polarity has prevailed, apart from assuring that mics have been aligned, if we're lucky. But inversions can creep in at consoles, peripheral gear, recorders etc. etc. If the mastering engineer is to do anything at all useful, he must determine the polarity of each cut and align them to one way or the other. Keep in mind, there is no "right" way at this point, and a study shows that recordings (CDs, LPs, tapes) are split 50/50 -- sometimes on each disc!

One of the most nonsensical statements I read here goes, "Telarc always made sure that their bass drums would produce an outward-going woofer [excursion] for most impact." And just how were they able to assure this?

That question is unanswerable, if you've been following my argument. Likewise, nothing the mastering engineer (or any engineer in the chain) can do will produce the desired polarity result at listeners' ears. Only the listener, sitting in acoustic space like the musical instruments themselves, can make "absolute polarity".

Absolute polarity, once learned, like bicycle riding can never be unlearned. But generally speaking, one must listen for it and "throw the switch" accordingly. Granted this may become tedious, but what else can one do when our mastering engineers continue to create product with both polarities, sometimes even alternating from cut to cut. (And what's up with that?)

So far as I know, only one device on the market attempts to determine polarity in acoustic space, the SMART System 2000 Sound Check from Smart Cinema Sound Products. I have used it and agree with its readings. Often, however, as you understand, a recording is so gemischt that no such determination is possible.

Hope that helps. The Wood Effect was published back in 1988 and contains over eighty references to polarity in the audio and acoustic literature, besides (if I may say) a wealth of corroborative information. Its author (yes, myself) had hoped that a book would settle the matter once and for all, but controversy and misunderstanding still flourish unabated.

clark

[bmanic]

Nice post! Welcome Clark!

Cheers!
bManic

[bob katz]

Originally Posted by clarkjohnsen

[

One of the most nonsensical statements I read here goes, "Telarc always made sure that their bass drums would produce an outward-going woofer [excursion] for most impact." And just how were they able to assure this?

It's not nonsensical when you supply the obvious missing parts that I thought would be obvious to an observer as perspicacious as you. But I'll supply the missing parts of the paragraph:

1) Telarc ensured correct absolute polarity throughout their signal chain.

2) The statement about the bass drum assumes that the listener's listener's reproduce system has been calibrated for correct absolute polarity. It's a syllogism.

For example, until I discovered that my Lipinskis were incorrect, then signals put on the so-called plus terminal produce the incorrect polarity on the Telarc bass drum.

3) In the analog days, since there was no official standard for magnetic coil polarity there was still a 50-50 chance of being right or wrong, but in digital the polarity of a digital signal is absolutely defined and therefore can be applied at the analog end to the loudspeaker.

4) Obviously the more minimalist the recording, the more that the acoustical wavefronts will align without ambiguity and throwing the thing into a mess.

All this stands to reason but does not reduce the requirement that the loudspeakers themselves must be polarized correctly.

I hope this supplies the obvious missing pieces and that we can move on from this nonsense.

BK

[Adam Dempsey]

Originally Posted by philip

no thats fine if you like to work that way. But the problem is there is no right or wrong with polarity, so even if you change polarity and it sounds better to you, this does not mean the polarity is "right".

If it's most true to the source then it is "right"...

When I go see a band I expect to see (hear) the drummer hit the drums from the outside of the drum, not somehow from within the drum. And I expect the front head of the kick drum to move forward towards the audience on beater impact.

Viewed as a wave form (see post #44 above)... what goes up must come down. Right now I just can't think of where 'what comes down must go up' occurs initially in nature.

But yes, as said, it's an interesting topic.

[bob katz]

Originally Posted by philip
no thats fine if you like to work that way. But the problem is there is no right or wrong with polarity, so even if you change polarity and it sounds better to you, this does not mean the polarity is "right".

That's not true. There is a MEASURABLE right or wrong, and it can be tested. There are some instruments which are known to produce definitive assymetrical waveforms. One of them is a muted trumpet, which has a distinctive negative-going peak. The other is the initial attack waveform of a bass drum.

So there is a "right", there is a "correct" which can be compared with nature and if the wrong way sounds better to you, then you are wrong! Objectively.

Why did they bother to invent polarity testers? (it could be argued to assist in the building of multi-way loudspeakers). Regardless, the polarity of a loudspeaker can be measured objectively with a polarity tester. So the phenomenon is scientifically measurable, it's simply debatable to what extent it is audible.

BK

[Lagerfeldt]

Just as the thread was about to die a horrible death it suddenly got interesting again.

[UnderTow]

Originally Posted by kategra84

i bet if you mix the two signals in the Polarity.wav or in the Picture above they will cancel out just as two phases of the same signal at 180°.

You are missing the point of my previous post: You can not shift the phase of that wave file by 180° because you can't speak of a specific frequency. It makes no sense to talk this way about the phase of a complex waveform as there is no specific frequency or period. It is only applicable to periodic waveforms. (Sine, Cosine, Square, Triangle etc)

Here is a nice animation that shows the relation between phase and time: Animation: movie of a sine wave (sinusoidal wave) y = sin x and a cosine wave y = cos x by Russell Kightley Media

I know many people will call a polarity inversion a 180° phase shift but that is wrong. Unfortunately much equipment/plugins, their manuals and other documents make this mistake which is probably the cause of the confusion.

Feel free to invert the polarity of the first half of the wave, align it with the second half and see if nulls (it should) but that doesn't change the fact that calling it a phase shift is wrong.

ps - when i'll get home i'll mix the tow signal to see what happens

What two signals? It is just a bounce from a section of sequenced music with only the kick and the bass soloed. The polarity is just flipped half way through by automating a plugin on the master bus (Flux Stereo Tools).

Alistair

[PatrikT]

Originally Posted by turtlerock

what i have done here is align our systems is using a emt phase gun as the master reference , we have made sure every single thing in our studios "pushes" as its first wave front impulse

I've just made sure things are "pushing" when coming back from analog if they are "pushing" when entering it.


Best Regards
Patrik

[Lagerfeldt]

Originally Posted by UnderTow

Here is a kick & saw bass with a polarity reversal half way through: http://puretone.nl/Polarity.wav

Alistair

One half sounds right, one half sucks, literally speaking. ;-)

I think that's a very clear example.

[philip]

Originally Posted by bmanic

Nice post! Welcome Clark!

Cheers!
bManic

+1 You are very welcome!

[kategra84]

Originally Posted by UnderTow

You are missing the point of my previous post: You can not shift the phase of that wave file by 180° because you can't speak of a specific frequency. It makes no sense to talk this way about the phase of a complex waveform as there is no specific frequency or period. It is only applicable to periodic waveforms. (Sine, Cosine, Square, Triangle etc)

Here is a nice animation that shows the relation between phase and time: Animation: movie of a sine wave (sinusoidal wave) y = sin x and a cosine wave y = cos x by Russell Kightley Media

I know many people will call a polarity inversion a 180° phase shift but that is wrong. Unfortunately much equipment/plugins, their manuals and other documents make this mistake which is probably the cause of the confusion.

Feel free to invert the polarity of the first half of the wave, align it with the second half and see if nulls (it should) but that doesn't change the fact that calling it a phase shift is wrong.

What two signals? It is just a bounce from a section of sequenced music with only the kick and the bass soloed. The polarity is just flipped half way through by automating a plugin on the master bus (Flux Stereo Tools).

Alistair

Yes Alistair you are right, it's not phase shift , I stand corrected
i didn't get the chance to mix the two halfs of that Polarity.wav , i'm sure they will cancel out each other.

Can you guys tell me how can i figure out if my mic recordings, or any other voice, have the corect Absolute Polarity ?

[bob katz]

Originally Posted by kategra84

Yes Alistair you are right, it's not phase shift , I stand corrected
i didn't get the chance to mix the two halfs of that Polarity.wav , i'm sure they will cancel out each other.

Can you guys tell me how can i figure out if my mic recordings, or any other voice, have the corect Absolute Polarity ?

In general it is not easy to tell from the waveform of the recording itself unless you have recorded a trumpet, trombone or a bass drum. The trumpet and trombone usually (but not always) have a distinctive negative-going peak. The bass drum should have an initial positive-going transient before then going negative. But if you have access to the microphone, cables, preamps and ADC that were used you can generate a signal with a polarity tester and look at the waveform in your DAW and confirm it made it through with the correct polarity.

BK