Absolute phase, etc.

Tam Lin

Well-Known Member
Mar 20, 2011
94
35
923
79
North Texas
Some audiophiles are sensitive to absolute phase. Normally, correction is done on a system-wide basis by swapping speaker leads or flipping a switch on the preamp or DAC. It’s inconvenient, at best. The Ambiophonic plugin I posted nearby has the ability to adjust a number of decoding parameters on a track by track basis, using the file tags, or on a folder by folder basis, using controls in a simple text file. The parameters not related to Ambiophonics effects are: level, balance, and per-channel phase. After installing the plugin, uncheck all boxes in the configuration dialog, set Level to 100, Balance to 0, and activate the BYPASS button to disable all RACE processing. Then check Tag and/or File depending on your choice of control.
 

Mark (Basspig) Weiss

Well-Known Member
Aug 3, 2010
678
31
940
New Milford, CT
www.basspig.com
Absolute phase is very important with assymetrical sounds like pyrotechnics. My Ultimate Fireworks Blu-ray disc has a positive voltage swing on the explosions, matching the polarity of the compression of air during each explosion. The sound pressure level is higher when the speakers are playing this with correct phase, so in this type of program, absolute phase is definately important.
 

Tam Lin

Well-Known Member
Mar 20, 2011
94
35
923
79
North Texas
Absolute phase is very important with assymetrical sounds like pyrotechnics.

The sound from any source that moves air is asymmetrical. The attached oscillographs are of singers Christina Branco and Nora Jones. The asymmetry is visibly and audibly obvious.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
3,946
305
1,670
Monument, CO
Of course, depending upon the frequency, moving back and forth a little can also change the relative phase... I have personally found absolute phase to matter only for initial percussive strikes (guess that puts me with Mark) and not for midrange stuff like vocals. Or perhaps I just find other things dominate the sound, at least to me.

Now for the "details matter" speeches (I do not necessarily disagree, just predicting what's coming).
 

Bruce B

WBF Founding Member, Pro Audio Production Member
Apr 25, 2010
7,002
508
1,740
Snohomish, WA
www.pugetsoundstudios.com
Phase and polarity are 2 different things...

Phase involves a stereo signal where the Left and Right signals are reversed, which is called "out of phase". Polarity is whether a signal is plus or minus. If a snare drum is hit and the transient goes negative instead of positive, then the polarity is reversed. Such, if an instrument has 2 microphones recording it and if both waveforms travel in opposite directions, one going up and the other going down, then the signal is out of phase and you will need to reverse the polarity of one microphone.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
3,946
305
1,670
Monument, CO
Good clarification, Bruce. I was trying to stick to the terminology in the thread and just made my head hurt.

Phase is also generally considered to be frequency-related whilst polarity is an absolute.
 

Speedskater

Well-Known Member
Sep 30, 2010
941
15
368
Cleveland Ohio
It's more complicated terminology than I thought.
I just had J. Gordon Holt's 1990 book "The Audio Glossary" out and here are a few definitions:

phase
(5) An expression of the relative polarities of a stereo pair of devices or audio signals. Out-of-phase means connected in opposite polarity (180° out of phase).

polarity inversion
Reversal of absolute phase, so as to reproduce original compression waves as rarefactions and vice versa.

polarity switch
A user control which reverses the absolute phase of a device's output signals.

and then there is:
absolute phase
(1) The correct acoustical polarity of sound waves, in which original air compressions are reproduced as compressions rather than as rarefactions.
(2) The electrical polarity of both stereo channels, which determines (1).
 

Mark (Basspig) Weiss

Well-Known Member
Aug 3, 2010
678
31
940
New Milford, CT
www.basspig.com
The sound from any source that moves air is asymmetrical. The attached oscillographs are of singers Christina Branco and Nora Jones. The asymmetry is visibly and audibly obvious.

Not ANY sound. A tuning fork is symmetrical. Vocals are highly aperiodic and asymmetrical. Well, most vocals. Some Japanese vocals I've analyzed are nearly perfectly sinusoidal on the higher notes. Pyrotechnics are the most assymetrical of all sounds. In fact, they have all positive rising voltage. The only thing that goes negative just slightly is the reverberation, which is several orders of magnitude smaller than the initial sound. On a scope, it looks like positive noise spikes through a rectifier.
 

Tam Lin

Well-Known Member
Mar 20, 2011
94
35
923
79
North Texas
I started this thread to point out a capability of the Ambiophonic plugin I posted that was probably overlooked: Namely, the ability to change the absolute or relative phase on a track by track basis. I didn’t intend to start another pissing contest about the audibility of absolute phase.

Some people are blessed/cursed with a sensitivity to absolute phase but can do little about it because there is no phase/polarity standard in the recording business. The apparent correct phase varies from label to label, disk to disk, and track to track. I found the addition of Ambiophonics acerbated the problem. For that, and other reasons, I don’t use any Ambiophonic effects. I do use the plugin to correct absolute phase, relative phase, and balance on a track by track basis.

Not ANY sound. A tuning fork is symmetrical.
A tuning fork does not move air. An explosion does. So does a singer.

Speaking or singing a 'P' syllable creates a burst of air which produces a distinct asymmetry in the pressure wave detected by a microphone or heard by a listener. There is only one correct way to reproduce that asymmetry.

Of course, depending upon the frequency, moving back and forth a little can also change the relative phase...

Really?
 

Mark (Basspig) Weiss

Well-Known Member
Aug 3, 2010
678
31
940
New Milford, CT
www.basspig.com
Sound IS air movement. If you can hear a tuning fork, then it is moving air. That's not debatable. It's existential fact. And explosion moves air too, albeit in the direction of pressure increase on the initial leading edge. Tuning form compresses and rarifies air, depending on which side of the forks the air is on.

It is awful that recording companies cannot maintain a standard polarity for recordings. Mine are always positive pressure induces positive voltage.
 

Speedskater

Well-Known Member
Sep 30, 2010
941
15
368
Cleveland Ohio
Sound IS air movement.
Really? Is that your definition of sound? Of course some air will move near the sound source. But when a lot of air moves, it's called wind.
 
Last edited:

Bruce B

WBF Founding Member, Pro Audio Production Member
Apr 25, 2010
7,002
508
1,740
Snohomish, WA
www.pugetsoundstudios.com

Yes really.... that's why when you record a single instrument with 2 mics, it is imperative that you listen for phase issues. Moving the mic back and forth even an inch or so can correct phase issues.
 

fas42

Addicted To Best
Jan 8, 2011
3,973
3
0
NSW Australia
Sound IS air movement.

Really? Is that your definition of sound? Of course some air will move near the sound source. But when a lot of air moves, it's called wind.
Rather than have this issue degenerate into a shouting match, it's probably best to clarify a couple of issues: air can move in a particular direction, and keep moving in that same direction, without reversing its movement. Wind is an excellent example, and is equivalent to DC, or battery current. Sound is actually vibration of the air molecules, back and forth, the air is moving first a short distance in a certain direction, then reversing its motion. Very rapidly, at a certain rate or combination of rates, that's what gives a sound its frequency, and harmonics, etc. There is no net or overall movement of the air anywhere, unlike wind, but rather a wave or ripple of vibrational air movement travels outward from the source of the sound. This is equivalent to AC, or mains current.

DC movement of air is useless for our ears, it's equivalent to a frequency of 0 Hz; our body will certainly feel that rush of wind, and it will subjectively add to the sound, but it is not sound in the accepted sense of how ears function.

Frank
 

Tam Lin

Well-Known Member
Mar 20, 2011
94
35
923
79
North Texas
Sound is propagated via a wave of alternating pressurized and rarified air. The individual molecules are not displaced beyond the range expected by their Brownian motion. Moving air requires the net displacement of a significant mass of air. A vocalist exhales while vocalizing. That moves air. Air from the lungs is displaced into the surrounding space. The exhalation of a vocalist will disturb nearby candle flame, a tuning fork will not.

I see this forum thrives on pissing contests. I'm all pissed out.
 

Mark (Basspig) Weiss

Well-Known Member
Aug 3, 2010
678
31
940
New Milford, CT
www.basspig.com
The reason a tuning fork will not blow out a candle is because the amplitude is too low. Periodic waves, when large enough in amplitude will blow a candle out, even levitate objects. Wind makes sound, too, just not in a range of frequencies we can hear. It's like DC with amplitude perterbations due to the turbulence of the air flow.
Air moves, whether its periodic or in one direction. The breath from a singer is a portion of the sound that is inaudible to the listener, unless it strikes the mic diaphragm and makes its own noise artifact. Air movement is vibration of air molecules. Sometimes that vibration falls outside the audible range and is aperiodic. But it's still air movement. Consider two speakers.. one is a dipole, the other a sealed baffle. The former behaves like the tuning fork, while the latter creates a sum total pressure change. The former creates no sum total pressure change, but locally, on either side of it's diaphragm, it creates localized pressure changes. The dipole speaker compares to the tuning fork, while the sealed baffle compares to the explosion.
Without air, you could not have sound. All sound is air movement. Some air movement falls outside the audio range.
 

Soundproof

New Member
Jan 13, 2012
429
1
0
Oslo, Norway
The two tines of a tuning fork are 180 degrees out of phase after being struck. If you raise a tuning fork from its resonator, and place a thin sound absorber between the two tines, the one closest to a listener or microphone will sound louder, since its twin tine is no longer cancelling its output.

Sound waves propagate through air in the same manner waves across a pond distribute energy from the point of initiation. But water isn't actually transported from the point of initiation at the speed of the wavefront, the pattern just reflects the energy imparted in the medium. Actually worth considering - or "ponder the pond" as one of my teachers used to say.

The air expulsed by a singer only causes turbulence in the medium - it is the ability of the singer to use air to create motive resonances with the vocal chords that impart energy through the air, in a way that can make crystal crack at a distance if it enters into sympathetic vibration with the energy transmitted from the vocal chords through the medium. Or that can be heard as mellifluous song.

Sound travels faster through more densely packed media, such as water or metals, because the molecules are more densely packed, and therefore transmit the imparted energy quicker. From this, we should realize the distinction between the transmitted effect and the medium it uses for dissipation.
 
Last edited:

bdiament

Member
Apr 26, 2012
196
0
16
New York area
Hi Speedskater,

It's more complicated terminology than I thought.
I just had J. Gordon Holt's 1990 book "The Audio Glossary" out and here are a few definitions:

phase
(5) An expression of the relative polarities of a stereo pair of devices or audio signals. Out-of-phase means connected in opposite polarity (180° out of phase).

polarity inversion
Reversal of absolute phase, so as to reproduce original compression waves as rarefactions and vice versa.

polarity switch
A user control which reverses the absolute phase of a device's output signals.

and then there is:
absolute phase
(1) The correct acoustical polarity of sound waves, in which original air compressions are reproduced as compressions rather than as rarefactions.
(2) The electrical polarity of both stereo channels, which determines (1).

Much as I admire Gordon's work, I think it can be stated more succinctly:
Phase is not polarity and polarity is not phase. But there is a relationship.

Phase involves time and polarity involves direction.

Phase deals with relative timing between two signals. Though the phrase "out of phase" is often used to indicate two signals of opposite *polarity*, it actually means they are not in time (or "in phase") with each other. In fact, the polarity of both can be the same but one might be a fraction of a wavelength behind or ahead of the other. The audible results can manifest themselves in a number of ways, from an odd frequency response to one musical "attack" being heard more than once. (Anyone old enough to remember television via antenna might also remember "ghosts", pale "echoes" of the main signal, seen slightly offset to one side from the main image. This is another manifestation, this time with video of course, of phase issues.)

Polarity, as I mentioned above, deals with the direction of the signal, its positive motion and its negative motion. Sound waves in nature, including from musical instruments and voices, are *not* symmetrical. As with everything in audio, different folks will have different sensitivities to this. Some will not hear a polarity reversal if both channels in a stereo signal are of the same polarity. Others will hear differences they'll describe as "subtle" and others will insist on being able to correct this on recordings that have it wrong. (This is complicated by typical multimic, multitrack recordings were different signals are in different polarities.)

A somewhat recent example of a recording that is in phase (with itself) but in reversed polarity from the original release is the Beatles' 2009 CD remaster of "Revolver". Compared with the original 1987 CD, one of the differences is the polarity (which I only tested -and confirmed- because I heard it when doing a listening comparison of the two). I'm told the 2009 matches the master tape. If that is the case, my ears make me suspect the error is then in that master tape. To my ears, the '87 CD, its limitations aside, sounds more "in focus".

In sum, the correct term *is* "absolute polarity" (as opposed to "relative polarity", a condition which, as I mentioned above, is often, mistakenly as I see it, referred to with the term "out of phase").

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com
 
Last edited:

Mark (Basspig) Weiss

Well-Known Member
Aug 3, 2010
678
31
940
New Milford, CT
www.basspig.com
Some early Fisher and other hi-fi amplifiers had a phase invert switch. This issue has been known for at least 50 years, but more recent hi-fi gear has dispensed with the polarity switch, so the manufacturers seem to consider it unimportant today.
 

Soundminded

New Member
Apr 26, 2012
289
1
0
Some early Fisher and other hi-fi amplifiers had a phase invert switch. This issue has been known for at least 50 years, but more recent hi-fi gear has dispensed with the polarity switch, so the manufacturers seem to consider it unimportant today.

Early Fisher and other stereo amplifiers only changed the phase of one speaker to allow easy correction of out of phase speaker wiring without disconnecting the wire at one end. At that time absolute phase wasn't even considered.

Looking at how objects vibrate, they fall into two categories. For string and percussion instruments the term absolute phase has no meaning. Different parts of the vibrating element that creates sound are moving in opposite directions at the same time. This means depending on where you are in relation to the instrument the first sound you hear from it may be either a compression wave or a rarifaction wave. Try walking around a harp player who makes sound by plucking strings. Can you tell by listening to a single note alone repeated again and again which side of the harp you are on? If you walk around a violin or cello while It is playing can you tell if all of the notes are only upbow or downbow which side of the instrument you are on? No because if you could see the string in slow motion it would look like wiggling wet spaghetti, different parts of it moving in different directions at the same time. Same for struck instruments like a drum head. The membrane of a struck drum will look like the surface of the ocean, some parts are moving up while other parts are moving down. This is how it creates harmonics. The mathmatical description is called a Bessel function.

However, for spoken word, singing, or horns (brass and reed instruments) the first arriving wave is always a compression wave. This is because sound is made by them by exhaling, never inhaling. Some people are sensitive to this difference, some aren't.

For older recordings before this became a concern, you probably have about a 50-50 chance of "getting it right." With multimiking, you may find some instruments on the same recording are in phase while others are out of phase. This is because in the recording/mastering/record cutting process, the signal passes through many amplifier gain stages. For a common cathode tube circuit and a common emitter transistor circuit, the most widely used amplifier configurations, anywhere along the way, there is a phase inversion between the input to that gain stage and the output. How many of them were in the circuit and how the microphone was wired are the determining factors. With typically up to 24 channels, where modules could be bypassed or inserted in the circuit it's the luck of the dice.

Phase and polarity are directly related because when a speaker is wired with one polarity, a positive going voltage will cause the cone to move forward creating a compression wave. With the speaker wired opposite it will move backwards away from you creating a rarifaction wave. The overall result is the net total of ALL of the gain stages with their inversions from the microphone output to your speaker input. Does it matter? I suppose if you are exquisitely sensitive to it it could although this is a relatively insignificant distortion for most people if they can hear it at all I think. Personally for me, I can't hear the difference.
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing