Absolute phase, etc.

KBK

New Member
Jan 3, 2013
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#21
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.
Thus an inability to hear a given thing may have the capacity to invalidate some given arguments about perception. For the absence of inherent capacity to ruminate upon a given thing is in the most basic sense...missing. As mentioned in another place, the base system of the ear/brain is plastic, not set in stone. If it was set in stone, we'd be, as humans, irrevocably hardwired unchanging boxes of wiring that fell off a cliff a long time ago. Of course, we tend to have components of that aspect, which is tied to some of humanity's issues, as it where, but overall, plastic and mutable. ie, capacity to change and learn. That you can teach yourself absolute phase, as an act of hearing and recognizing, if you desire to do so.
 

Orb

New Member
Sep 8, 2010
3,022
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#22
Tonight, we went to a pub to hear an irish band, 4 guys playing hand held drum thingies, squeeze boxes, violins, fiddles, guitars of various sorts, flutes, accordians and bells and stuff.

These guys were totally unamplified. No electronics anywhere. Here is an interesting thing I noticed tonight in that pub room. It was about 40 feet high and at the end of the pub which was maybe 30 feet wide. We were at a table, same height as them and sitting down, and about 15 feet away from them, no one in front of us. And about 30 degrees from dead center, we were closest to the violin player, who was on our left as we faced the group.

Anyway, while I watched and listened, (and unfortuneatly for me always comparing to what stereo can do) I found that while sighted, say the drum for example, the sound came from that fairly specific area of the drum as I saw it, and the same with the violin, although there was some movement in a slight vertical angle depending on how he bowed it, sometimes it got a bit wider on the lower notes.

Anyway, close the eyes, head in exact same spot, same song playing, guess what, now I am very much aware of the echos an reverb, and the drum is now in two places, its originalish spot and somewhere near the wall where it is bouncing off of, and the violin, whoa baby, on some notes that thing extended 4 feet or so in width.

It was eye (ear) opening, the effect of sight on the brains processing of the sound. The brain certainly can refine what the sound is when it is also getting visual stimuli.....but close the eyes, and it has to "open" up to all the info coming in and try to make sense of it as best it can. Just another reminder for me about how much processing is done in the brain or ear/brain interface, and the bias that sight provides. Interestingly, in this case, there was not much height information sighted, but seemed more when not sighted, due to the brain focusing more on the reflections I suppose.
Yeah, why I have mentioned in the past about sight-perception bias and how some are critical of electronics bias but never consider the effect when listening to speakers; with speakers the sight-perception-location bias is pretty large.
Not directed at you but glad you mentioned your experience as it ties in with what I mention briefly now and again when some are a bit selective on biases and nearly everyone ignores sight-location-environment perception related biases.
This has been shown to skew results in speaker preferences as much or if not more than brand/perceived value bias.

The following example is my own personal view and only circumstantial but this is one reason I feel those audio improvement-tweak bowls located around a room can work for those listening, well at least one reason anyway as it ties into the above and also a bias that adding said product we see a change in environment and works on our cognitive in that the change therefore will have a causal effect to what we are listening (trying to avoid word "expectation" as it is not technically expectation bias).
I am not disputing they work, just that this is one cognitive mechanism that is also in play and makes it interesting from a technical perspective on auditioning-reviewing-measuring/analysis.
In a rush so apologies for a very crude example/writing.

Cheers
Orb
 

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