Phase as an issue in audio.

[PaulStewart]

Single driver planar speakers are among. the most phase coherent available, the Orchid monitors which came from a recording studio heritage used extra drivers to create error correction. These sounded very accurate, in fact I did once emntemr discussions with the designer to market them. I did design a couple of phase coherent monitors using time correction back in the day. In those days it was all analouge, hese days it's much easier to do it in software. I find that old Tannoys with suitably modded x-overs are very good in terms of time and phase accuracy.

[nat8808]

It's more to do with the leading edge of transients, Jerry. Does a drum kick pressurise the air or 'suck' on the initial kick?

Are you in front of the drums or behind them?

How about a test that doesn't involve the reproduction chain? Just stand on different sides of a real sound source and try to work out if it sounds different..

[nat8808]

Yep, Dave, bass freqs fair enough - 1/50th of a second say, may well be a significant portion of a transient and so easily discernible - but I'm hearing plain and obvious changes to the soundstage and perceived detail well into the midrange freqs and above!

As to proof of cable differences --- let's not go there! (says me, a buyer of expensive foo cables! )

I'm not sure if I can hear the difference personally (only test has been changing phase by remote on a Meridian CD player).

However, it could effect soundstage perhaps.. Im mixing science here but our ears do apparently use phase to determine a 3D soundstage (I remember a Tomorrow's World transmission showing 3-D sound placement technology via a simulatanious Radio 1 broadcast - sounds moving around outside of the speakers etc).

Here's a POSSIBLE analogy, perhaps.. from a wiki on holography:

Process

When the two laser beams reach the recording medium, their light waves intersect and interfere with each other. It is this interference pattern that is imprinted on the recording medium. The pattern itself is seemingly random, as it represents the way in which the scene's light interfered with the original light source — but not the original light source itself. The interference pattern can be said to be an encoded version of the scene, requiring a particular key — that is, the original light source — in order to view its contents.

This missing key is provided later by shining a laser, identical to the one used to record the hologram, onto the developed film. When this beam illuminates the hologram, it is diffracted by the hologram's surface pattern. This produces a light field that is identical to the one originally produced by the scene and scattered onto the hologram. The image this effect produces in a person's retina is known as a virtual image.

My emphasis added.

Consider a sound recording to also include an interference pattern of all the different pressure waves accross the microphones. I could imagine that say a Blumlein pair or some other stereo recording set-up would provide an interference pattern more easily recreated by stereo speakers (should speakers be spaced the same as the mics?).

It's quite possible in my mind that simply replaying the sound with a reverse phase can change phase-related interactions in a way that re-shapes the soundstage. If you reversed the phases interactions in a hologram it would in someway appear differently - maybe even preventing a complete virtual image from appearing.

Possible.. who knows? Not me, that's for sure!

[MartinT]

Are you in front of the drums or behind them?

My basic physics tells me it doesn't matter. A transient pressure wavefront will move outwards in all directions from the drum.

[jandl100]

I'm not sure if I can hear the difference personally (only test has been changing phase by remote on a Meridian CD player).

However, it could effect soundstage perhaps.. Im mixing science here but our ears do apparently use phase to determine a 3D soundstage (I remember a Tomorrow's World transmission showing 3-D sound placement technology via a simulatanious Radio 1 broadcast - sounds moving around outside of the speakers etc).

Here's a POSSIBLE analogy, perhaps.. from a wiki on holography:



My emphasis added.

Consider a sound recording to also include an interference pattern of all the different pressure waves accross the microphones. I could imagine that say a Blumlein pair or some other stereo recording set-up would provide an interference pattern more easily recreated by stereo speakers (should speakers be spaced the same as the mics?).

It's quite possible in my mind that simply replaying the sound with a reverse phase can change phase-related interactions in a way that re-shapes the soundstage. If you reversed the phases interactions in a hologram it would in someway appear differently - maybe even preventing a complete virtual image from appearing.

Possible.. who knows? Not me, that's for sure!

Hey, thanks Nat - the first person to even try to address my question about why differences at the millisecond level should be audible!

Hmmm ... I'm going to have to ponder on the optical interference analogy ... I suspect I may be out of my depth here!

If everything is reversed in phase, does that actually stop the interference from happening at each frequency, or would the interference still happen but with the interference pattern reversed in phase as well? ... Hmm ...

[nat8808]

Here's a small wiki with some further links inside:

http://en.wikipedia.org/wiki/3D_audio_effect


Sometimes complex systems completely flip and change in reaction to small variations - chaos effectively. Complete soundfields (pressure wave fields?) are immensely complicated!

[smalleyexy]

As an engineer, started the noise and vibration sensor life has made ​​me fascinated with this hobby, I think particularly interesting microphone pickup cartridge and speakers.

[PaulStewart]

Nat, your analogy with holography is an interesting and in my opinion, correct one. *Audio sound waves all interact with one another in much the same way as laser interference patterns do and, inasmuch as we can view holograms now without using a laser, white light viewable lasers are quite common, so we have these interference patterns in audio or as is more normal to refer to them in this sphere, these intermodulation products. **Research from the early 80s showed that reproducing sound below 20 Hz gave listeners a greater perception of realism when listening to recordings which had been made in such a way as to encode an original live acoustic. *Likewise, the adding of supertweeters, which can produce sounds above 20 KHz would help to sort out not only upper frequency reproduction, but also in many cases seems to smooth out problems in the base area. *How can this be? *It would appear that the brain perceives the intermodulation between the audible and inaudible frequencies as an important part of our perception of reproduced sound. *Interestingly, although we know that base frequencies are omni-directional, it has been found adding a base pulse to sirens on emergency vehicles helps people, especially blind people, to locate the vehicle by audible means more precisely. *Again, researchers believe it is the intermodulation between the audible frequencies of the siren and the bass, which cancels out the reflections off buildings etc that often make people unable to locate the direction from which the siren is coming.

How does this relate to phase accuracy in HiFi reproduction. *It would be my contention, and this is borne out by research that I have done and read, that when gross errors of phase occur in the reproduction chain, especially when they are at selected frequencies within the audible band, *then these intermodulation products do not occur correctly and the brain's ability to perceive the sound as "right" suffers. *

Research that Sony carried out in the 80s showed that, provided a system produced phase accurate reproduction that went as low as 10 Hz, then even using just small drivers with limited frequency response to produce the upper frequencies still provided a more realistic experience for listeners than a system that wasn't producing these intermodulation products with the inaudible sub 20 Hz signals. In fact even minor changes in phase on a system such as this caused a lack of perceived realism. *It is a fascinating area and one which, if I had the time, I would like to do a lot more research in. *Maybe when I win the lottery.....

[The Grand Wazoo]

As an engineer, started the noise and vibration sensor life has made ​​me fascinated with this hobby, I think particularly interesting microphone pickup cartridge and speakers.

'Johny' would you please comply with the request that I haver placed on your profile page?
Thank you.

[StanleyB]

*It is a fascinating area and one which, if I had the time, I would like to do a lot more research in. *Maybe when I win the lottery.....

I have been spending time on researching this phase issue and incorporating it into my DACs as modifications up to now. The Bushmaster will be the first DAC with some of my research built into it from day one. But I haven't disclosed the reason behind why I did it the way I did it for obvious commercial reasons. It's my livelihood after all . Probably the most successful implementation of it is in the Gator upgrade where I used a tiny amount of feedback so that the signal is not swamped by feedback induced phase errors.
Phase errors come in different forms and shapes, and no single solution can take care of each type. But by reducing or eliminating any of them does make an impact on the overall signal.