I've got a simple question for those who claim that they can hear absolute phase. Which one is it?
It's pretty arbitrary to post my question here. I do it because I am especially interested in hearing an answer from Nelson Pass.
I am a sound engineer, and I don't hear absolute phase. I hear phase anomalities, and I hear the moment when you change polarity ("flip the phase" - phase is actually a term for a time domain phenomena, while polarity is the correct term for what we're talking about). But I don't get the talk about "absolute phase" (intellectually I do, of course, but physically and physiologically I have doubts).
Consider a kick drum. When the drummer kicks the kick drum, the skin moves forward first. Now consider the microphone in front of the drum. What happens to its diaphragm at that moment? It moves backwards. So the polarity of the wave has been reversed. This wave with its polarity is what is actually recorded. NOT the polarity of the wave that emanated from the kick drum, but a polarity reversed copy of it.
If we take for granted that the mixing engineer and the mastering engineer don't alter anything in the phase or polarity of the signal (which is far from being a given - very common alterations vary from none to polarity reversal to frequency-specific phase rotation), the loudspeaker will reproduce what the microphone has recorded. This has a reversed polarity in relation to the wave that originally emanated from the drum.
So which is the "correct absolute phase"?
Do you reverse the phase of everything you're listening to, because then it represents the polarity of the original? Which one is the "right" "absolute" phase?
And do I understand it correctly that this whole discussion about absolute phase is strictly about the onset of a wave, and non-periodical signals like short transients? Because once the wave has started, it's a wave, a continuum. I must admit that I don't get the whole concept, but that's yet another topic.
EDIT: The simple solution that polarity is reversed in the microphone' setup (coil and magnet orientation in a dynamic microphone, for example) or in the wiring in order to represent the polarity of the signal recorded didn't occur to me. Thanks to all who pointed that out!
Some other aspects of my wondering still remain open, though.
It's pretty arbitrary to post my question here. I do it because I am especially interested in hearing an answer from Nelson Pass.
I am a sound engineer, and I don't hear absolute phase. I hear phase anomalities, and I hear the moment when you change polarity ("flip the phase" - phase is actually a term for a time domain phenomena, while polarity is the correct term for what we're talking about). But I don't get the talk about "absolute phase" (intellectually I do, of course, but physically and physiologically I have doubts).
Consider a kick drum. When the drummer kicks the kick drum, the skin moves forward first. Now consider the microphone in front of the drum. What happens to its diaphragm at that moment? It moves backwards. So the polarity of the wave has been reversed. This wave with its polarity is what is actually recorded. NOT the polarity of the wave that emanated from the kick drum, but a polarity reversed copy of it.
If we take for granted that the mixing engineer and the mastering engineer don't alter anything in the phase or polarity of the signal (which is far from being a given - very common alterations vary from none to polarity reversal to frequency-specific phase rotation), the loudspeaker will reproduce what the microphone has recorded. This has a reversed polarity in relation to the wave that originally emanated from the drum.
So which is the "correct absolute phase"?
Do you reverse the phase of everything you're listening to, because then it represents the polarity of the original? Which one is the "right" "absolute" phase?
And do I understand it correctly that this whole discussion about absolute phase is strictly about the onset of a wave, and non-periodical signals like short transients? Because once the wave has started, it's a wave, a continuum. I must admit that I don't get the whole concept, but that's yet another topic.
EDIT: The simple solution that polarity is reversed in the microphone' setup (coil and magnet orientation in a dynamic microphone, for example) or in the wiring in order to represent the polarity of the signal recorded didn't occur to me. Thanks to all who pointed that out!
Some other aspects of my wondering still remain open, though.
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Follow-up question from someone with no expertise of any kind: if the wave of the kick drum pushes in the diaphragm of the mic (retracts), is that recorded as a ‘positive’ peak amplitude? If it were, and the signal made it through mix and master unaltered, that positive amplitude would translate into an outward motion of the loudspeaker?
I should stop now, as I’m exposing more of ignorance than usual…
I should stop now, as I’m exposing more of ignorance than usual…
In that example, the positive (outward) pulse from the drum is mimicked by the outward pulse from the speaker.
So to my thinking, they are in phase.
The goal is as Colin suggest.
With some instruments the “out” is a bit differnt from the “in” and some can hear that if it is backwards.
You are trying to reproduce the sonic field the instruments have made.
dave
With some instruments the “out” is a bit differnt from the “in” and some can hear that if it is backwards.
You are trying to reproduce the sonic field the instruments have made.
dave
The OP can of course wait for NP's potential response. However, I've personally never seen NP discuss a "correct" absolute polarity (or phase). I've seen him discuss (or simply state) whether certain circuits maintain the polarity (phase) of the original signal or if they reverse (invert).
What I've been fascinated by is the discussion (and my own perception of sonic differences) re: how the phase of the distortion products (particularly the 2nd harmonic) relate to the phase of fundamental. Again, I've never seen a discussion re: what's "correct" only that there does seem to be a division among preference. Call it a bipolar response, if you will. 🙂
Among those that have achieved distortion levels well below the threshold of human perception, it seems moot.
What I've been fascinated by is the discussion (and my own perception of sonic differences) re: how the phase of the distortion products (particularly the 2nd harmonic) relate to the phase of fundamental. Again, I've never seen a discussion re: what's "correct" only that there does seem to be a division among preference. Call it a bipolar response, if you will. 🙂
Among those that have achieved distortion levels well below the threshold of human perception, it seems moot.
From the mic article linked below:
Microphone Polarity
A microphone accepts sound and turns it into audio.With unbalanced microphones, a displacement of the diaphragm inward should typically produce a positive amplitude in the microphone signal. This is because the start of a transient should produce sound pressure that moves the diaphragm backward. This is referred to as positive polarity.
https://mynewmicrophone.com/microphone-polarity-phase-how-they-affects-mic-signals/
And positive polarity moves a loudspeaker diaphragm forward, so it all fits. If I recall correctly, there is an AES standard defining positive polarity for everything from microphone to loudspeaker, including analogue tape recorders and vinyl records.
Continuous waves can be quite asymmetrical. Just say "book" into a microphone and look at the waveform of the "oo".
Continuous waves can be quite asymmetrical. Just say "book" into a microphone and look at the waveform of the "oo".
True, as far as the diaphragms (drum skin and microphone diaphragm) are considered "mechanically/acoustically" but microphone (think a dynamic one for this example) has a voice coil, which can be wound one or the other way (so 2 polarity possibilities) and a magnet, which can also be magnetized one or the opposite polarity.
And any pair of combinations can be chosen independent of what the mic diaphragm is doing, so conventional wisdom is to push diaphragm in and check output, so positive voltage matches positive drum "positive" (outward movement), so speaker (after a long chain) mimics that.
Agree that drum positive and negative sound (and feel) different if you are close enough, been there, done that; specially at a subsonic level (you feel it in your chest).
Now, after a frequency limited recording and even more frequency limited speaker ... not that much.
In a mic the element going in is considered positive because when played back it moves the speaker in the outward positive direction to corespond with the recorded live signal. More important is that all mics, patchbays, mixers, recording devices are all wired the same way. That way all the phases are the same polarity relative to each other. Also, when done that way phase can be controlled intelligently where it is desired instead of by chance that one mic is out of phase because it’s wired wrong. In the old days some companies, I’m looking at you Sony, used to be pin three high causing all sorts of issues when mixed with other equipment. It is easier to compress air than rareify it so positive absolute phase is thought to give more impact and edge to the sound but it is minor.
Thank you all for all the interesting input!
The last sentence above (and also the statement about asymmetrical wave forms) is a good hint towards more understanding of what "them" hear.
It was my understanding that NP stated that he can hear absolute phase. Relative phase of harmonics to the root is a different topic. NP stated that different polarity of 2nd harmonics in relation to the root leads to a different presentation of depth. I have yet to study that in the studio.
The effect of the polarity on the sound is quite subtle; there has been at least one study showing that polarity changes are audible in music under double blind conditions, but they only found an effect with acoustically very dry recordings played back in mono in an acoustically dead space if I remember well.
I believe I can hear it too, and my gear is similar to Nelson’s. What makes it work is a reasonable amount of second harmonic content with very little of higher order harmonics. Very little distortion or very clean FFTs don’t make it work either.
For most recordings, with one polarity, the entire soundstage moves closer to you and instruments are easier to locate, everything is big and natural. With the opposite phase, soundstage moves farther away and less enjoyable (to me). Some recordings I find myself flipping the polarity in JRIVER and some others I leave it alone. When playing records I noticed I preferred opposite polarity to my digital sources. Just learned about the reason today: Pearl II phono pre inverts phase.
For most recordings, with one polarity, the entire soundstage moves closer to you and instruments are easier to locate, everything is big and natural. With the opposite phase, soundstage moves farther away and less enjoyable (to me). Some recordings I find myself flipping the polarity in JRIVER and some others I leave it alone. When playing records I noticed I preferred opposite polarity to my digital sources. Just learned about the reason today: Pearl II phono pre inverts phase.
My psycho-acoustics expert informs me that there is indeed a physiological mechanism in the ear for discrimination of phase, this information being relatively new, but somewhat contradicting the wisdom of a century ago.
My own impression is that variations in relative phase and group delay are audible, a fine example being the sound of last month's Speaker Camp project, where reversing the phase of one of the drivers gives little difference in amplitude response but a large difference in sound.
My own impression is that variations in relative phase and group delay are audible, a fine example being the sound of last month's Speaker Camp project, where reversing the phase of one of the drivers gives little difference in amplitude response but a large difference in sound.
I would say that relative phase is certainly audible! Even though I notice while writing that I haven't actually tested this thoroughly. There are plugins which let you reverse the polarity of specific harmonics. I will experiment with them. NP stated that reverse relative polarity of 2nd harmonics shifts signals further back, if I recall correctly.
Relative phase alterations are actually very common in sound engineering.
For example, there's something called all pass filter that is frequently used in studios. It shifts phase around, while the frequency spectrum stays unaltered. It is said to help the bass sound tight and orderly.
An equalizer alters phase relations, unless it's a linear phase equalizer, which leads to the problematic artifacts of pre- and post-ringing (the pre ringing is problematic, especially at low frequencies, since you can hear it as a distinct sound, while the post ringing is masked by the actual sound of the original signal).
Absolute phase, on the other hand, means polarity of the signal as a whole, as far as I understand. There, I'm skeptical about whether you can hear it. Even though the point of "It's easier to compress air than to expand air" is interesting, and seems worth exploring.
And the point about feeling a subsonic push differently than a subsonic "suck" seems legit, too.
Relative phase alterations are actually very common in sound engineering.
For example, there's something called all pass filter that is frequently used in studios. It shifts phase around, while the frequency spectrum stays unaltered. It is said to help the bass sound tight and orderly.
An equalizer alters phase relations, unless it's a linear phase equalizer, which leads to the problematic artifacts of pre- and post-ringing (the pre ringing is problematic, especially at low frequencies, since you can hear it as a distinct sound, while the post ringing is masked by the actual sound of the original signal).
Absolute phase, on the other hand, means polarity of the signal as a whole, as far as I understand. There, I'm skeptical about whether you can hear it. Even though the point of "It's easier to compress air than to expand air" is interesting, and seems worth exploring.
And the point about feeling a subsonic push differently than a subsonic "suck" seems legit, too.
Please. When you make a statement like this, if not provide a link, at least name them. I cant imagine a harder Google search. https://integraudio.com/7-best-phase-alignment-plugins/ Only 7 to pour through to see if any operate on "specific harmonics"...
I think the book "The Wood Effect: Unaccounted Contributor to Error and Confusion in Acoustics and Audio" was about absolute phase. I used to have a copy, but lost it at some point in the past 25 years. Author Roger Clark Johnsen of Boston's "The listening Studio" apparently died within the last couple years, RIP. I met the guy one time. He said different tracks on the same LP can have different "absolute phase". I guess that's why the switch was provided on some preamp designs.
On my system I'd need a 8PDT switch on the amp outputs. I saved a 4PDT switch for that all these years; never used it.
On my system I'd need a 8PDT switch on the amp outputs. I saved a 4PDT switch for that all these years; never used it.
There is PKHarmonic that lets you play with the relative levels of harmonics.
https://distortaudio.org/pkharmonic.html
I have tested it extensively within JRiver. To me, it imparted a subtle but noticeable effect. I used it with a "clean" amp like the Hypex UCD and significant amounts of H2 improved the sound (sweetened it, really). Those class D amps sound harsh to me in the treble, they are nowhere close to the sound of class A.
But the effect is not the same as a really good class A amp producing primarily second harmonic distortion. I wonder if the reason is because of how the amp scales distortion linearly with level. For example, whatever the instantaneous db is of the music waveform, PKHarmonic will impart, say, -60 db H2 to it. Now, the H2 imparted would be at -60 db whether the waveform is at -20 db or -3 db. In other words, when a singer sings forcefully versus softly, you still get H2 at -60 db. Whereas with an amp, that is most likely not the case.
Nevertheless, it is a very interesting plug-in to try. Whenever a higher order harmonic level is higher than a lower order harmonic, it is very much noticeable and not likeable. It doesn't let you adjust the phase of the harmonics, but that has been requested as a feature.
https://distortaudio.org/pkharmonic.html
I have tested it extensively within JRiver. To me, it imparted a subtle but noticeable effect. I used it with a "clean" amp like the Hypex UCD and significant amounts of H2 improved the sound (sweetened it, really). Those class D amps sound harsh to me in the treble, they are nowhere close to the sound of class A.
But the effect is not the same as a really good class A amp producing primarily second harmonic distortion. I wonder if the reason is because of how the amp scales distortion linearly with level. For example, whatever the instantaneous db is of the music waveform, PKHarmonic will impart, say, -60 db H2 to it. Now, the H2 imparted would be at -60 db whether the waveform is at -20 db or -3 db. In other words, when a singer sings forcefully versus softly, you still get H2 at -60 db. Whereas with an amp, that is most likely not the case.
Nevertheless, it is a very interesting plug-in to try. Whenever a higher order harmonic level is higher than a lower order harmonic, it is very much noticeable and not likeable. It doesn't let you adjust the phase of the harmonics, but that has been requested as a feature.
As others have mentioned the drum head moving outward creates positive pressure at the mic diaphragm. Most mics specify positive pressure to produce a positive voltage on XLR pin 2 relative to pin 3. So there's no polarity inversion there unless mis-wired.
Downstream electrical polarity is a coin-toss. Polarity inversion is clearly visible on voice, sax and a lot of other instruments. DAWs will show the inverted waveform and engineers who are aware of polarity audibility can then correct it at the track level.
I can usually hear it on instruments having high even order content and therefor high waveform asymmetry. These instruments usually have high crest factor as well.
Positive pressure at the ear generally sounds a little brighter and more forward. Reversed polarity on sax for example generally sounds sucked in with a lot of reed and "lip." Correct the polarity and you get more of the bell tone of the instrument. Kick drums that produce positive pressure at the ear have more "point."
Artist Eric Johnson has been said to be very polarity-aware in his productions.
Anyone can check absolute polarity using their own voice: The glottal pulse of speech produces positive pressure; vowels are best. So you can use your voice as a signal generator to look for electrical inversion up to the speaker terminal.
It's always a good idea to make sure a positive voltage on the speaker "+" terminal actually pushes the woofer out.
I've done a number of experiments pulsing a live room with LF single-cycle bursts. With the polarity reversed at the source the character of the slap echo changed. Never been able to explain that one.
Also did an experiment with two versions of a short sax track and asked several allegedly-seasoned recording engineers what the differences were. I got "brighter/duller" "different takes?" comments and questions. Spoiler alert: They were exactly the same file; the only difference was one was inverted in Cool Edit.
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If I had recalled which one it is, I would have named it!
I myself am hoping I'll find it again... It's a distortion plugin, so these harmonics are generated, not extracted from the original signal.
Sorry for not being fully clear!