Phase as an issue in audio.

Hi Guys

This was meant for a thread that doesn't exist now...probably a good thing. However some of my thoughts are worth sharing.

Firstly something I want to get of my chest...

I for one dislike having other people tell me that I can't hear certain things, that I know I can hear (note I said can hear not necessarily explain )....they trot out the usual narrow world view and say if you can hear it you must be deluded or self delusional or its some sort of placebo effect. It may just be that my hearing is better or my system is more transparent. However I have always heard such things even when my past systems have not been as transparent as my current one is. It also bugs me when those nay sayers also then blame something else to account for what they themselves may be hearing but don't want to admit, either to themselves or God forbid some one else. Why can't they just say I can't hear it and leave it at that ? Answers on a postcard too..... I suppose its a lot easier to keep face if you have always been open minded, especially if you hear something improve a system which is way out there. I for one would rather say " Look I heard this...I can't explain it but check it out you may benefit ". Whats the harm in that ? It may work in that other system/application or not as the case may be. Is it not better to share and possibly help some one else get closer to their dream. Than keep silent because you might look a bit silly or crazy.

I offer this as an example...of the above.

When I recently reviewed Stans Beresford Dac 7510 I found it to be a bit fussy about what it sat on (lets say you can improve its sound with a bit of care and attention to set up and what it sits on). So when it was reported elsewhere that moving it to a stand sounded better and I would not for a moment show any surprise when moving it from a card board box top to a dedicated stand should show an improvement in sound. Its only logical to think that would be the case. Why should it not be so ? Unfortunately there are some who for what ever reason or agenda won't admit to such things and question it when they hear such things....fine let them be happy as they are, but equally they should stop trying to save us from what they perceive as our collective deluded states.....guys get a life please...do you want to be the audio Talaban and kill us next for what we believe we can hear. We don't need saving from having open minds and ears.

I have written the above because phase issues also seem to generate heated discussion and blanket statements that it does not matter or can't be heard. I think it matters and can be heard.

Any way back to the main topic of this thread PHASE.....does it exists as an issue. Yes. I firmly believe that in my experience it does and I believe that there are three main areas in which this is a potential problem.

One-Recording phase....from instruments to microphones to mixing desk to mastering to final medium (vinyl, cd etc)

Two-The design of audio kit and how it links to other item in the same brand or other brands.

Three- The design and implementation of balanced circuits and the difference between European wiring of the XLR plug/socket and the American.

The first one is really out of our control. I would have thought with so many connections (in the chain) and the possibility of many hook up errors. That these would be neutralized by the time the signal reaches the end and becomes a disc. That it may as a factor only effect a small number of recordings (either by accident. Or how many by design perhaps ?). I for one would have liked all gear (used for recording) to be set up and used properly (taking phase into account). However with issues two and three being also a potential factor, it is not a simple matter to sort out and the people as a whole involved in recordings etc would have to be pretty anal to sort it (even worry about it)....not very likely in most cases I would say. So if you want to look for phase issues in recordings or you know its an issue with a particular recording...go on flick/push the button and see what happens, or swap your speaker leads...takes but a moment to do. You never know you may hear it and like the change you have made.

The second issue. Ummm...this is more complicated in so much as should the spec of a product say it inverts phase....I for one would say Yes. This info should be present in the spec sheet (with every product and all the time) or mentioned as a last resort as part of a review. However if a designer feels his gear sounds better this way (valid design choice within the context of some one who makes items to be used together, such as a pre and power amplification system) but he/she should keep it in mind that their design may be used outside of their brand. If they make only one item, a power amp or pre then it would be vital to make known all specs so one can take these into account for proper matching (at least from a technical stand point). Phase issues aside this may not be an issue from a sonic/sound characteristic match up.

The Third issue is one I for one have plenty of direct experience with. My first cdp to have balanced outputs was my Marantz CD7, it is wired to the American system the + and - pins are wired in reverse to the European inputs and plugs...thus causing a phase issue. Wanting to have the thing wired right (maybe I am a bit anal about things like that), I spoke to a cable maker (who hadn't thought much about this either) and got him to wire a cable for me with the wires at one end (source ) wired for the swap with the + and -. It made, to my (deluded) ears a big difference in sound effecting the whole frequency and offering improvements in focus, bass and how fine detail was presented. The amplification in this case was Pathos Classic Ones. It was worth doing. Since that time I now have a pre-amplifier ( BAT VK31Se) with a phase switch button and I always set for the wiring of any set up American to European or vice a versa. Of course if your source to pre to power involves a couple of such swaps they can correct themselves by the time the music reaches the speakers. Swapping speaker + and - will not correct for a number of phase reversals upstream. So it is vital to know where these are and work accordingly.

Before I was aware of this as an issue I rarely heard/read much about it and now that I am aware of it the same is true. To my mind the ideal would be to set a world wide standard and wire accordingly with no worry. However including phase buttons on sources, pre amps and maybe power amplifiers might be a good idea accept that it adds something else into the path of the signal, and we really don't want to do that. Keep it simple....so correcting for wiring should really be kept out of things...at least in an ideal world, which this isn't. :(

There are also some who can't hear ( as opposed to wont hear ) phase issues...it would be nice to be like that, but I can. So blessing or curse I have to live with it.

Discuss the above. Peacefully Please.


Regards D S D L---Neil :)

"One-Recording phase....from instruments to microphones to mixing desk to mastering to final medium (vinyl, cd etc)"

Goldfrapp appear to record everything inphase so you can use them as a good reference.

Hi MarkF


Goldfrapp....good I like them a lot, though it took me awhile to get into their last record (sound not as good as previous albums either). However I do use their music for testing as well as pleasure so I will try switching phase and see what I think. Thanks for the heads up on that Mark F

For me phase only ever became an issue when I started exploring kit with balanced XLR connections and I was mixing European and American items. In order to get the connections right I decided to have a cable wired with the + and - pins reversed, so the signal reached the amplifier right way round. After playing around with cables that were not wired to correct this problem, I found I could hear when it wasn't right. One of the reasons I bought my current pre-amplifier was its ability to switch phase. I have a mixture of European and American balanced kit and this solution was better than having to get two sets of interconnects made one set for use between matching wired items and a set to allow for differently wired kit. This would have been to dear. Strangely swapping speaker leads round did not sound right compared to using an interconnect to solve the problem.

I think my biggest issue with all this, is the lack of info that many companies fail to provide with their products and whether phase is reversed or not would be the kind of info that would be useful to have. It should be mandatory and included on their products spec sheet/list.

This is a multi faceted problem (if you view it as such of course) and recordings which are not presented with correct phase only confuse things. How many people are phase sensitive and don't know it ? How many of them are using systems that are wired/connected out of phase, and perhaps their issues with the sound of that system are related to phase, but they just don't know because of lack of info. I was shocked by how many in the trade had never thought about the wiring of XLR plugs and sockets, and how that difference could effect sound. If you run balanced products from Europe and America or vice a versa and you are using a standard XLR cable or you have never switched phase (and you can on your source or pre)...can I suggest you do so, because you are currently some times (depending on source) listening out of phase. I think you will be surprised by what you hear....go on try it.

I must admit to not having given thought to corect pahase with RCA wired kit....worth looking into, I think.


Regards D S D L----Neil :)

I would go as far to say that "inverted signal" (which is what you are actually referring to) doesn't make a difference when the equipment is able to treat both polarities of the signal equally.

However not all equipment is able to do this. Solid state running in class A with little headroom or valves, microphones and speakers certainly don't. So its entirely logical that a difference could be heard.

So you are not mad after all about this subject anyway. Now about your Dalek identity crisis, take that plunger out of your mouth and come here..................:lol:

From The Grave

An interesting and timely resurrection!

My Krell KRC-3 pre-amp has remotely controlled polarity inversion, so I can just click the changes from my listening chair.

There is often a substantial difference, with (usually) the inverted position giving significantly more focussed imaging.

Neil describes the changes he hears as "... a big difference in sound effecting the whole frequency and offering improvements in focus, bass and how fine detail was presented." Mmm ... I don't think I hear any bass differences, but then most of my music is not bass-led so maybe that isn't high up in my listening priorities, but midrange & treble focus and fine detail for sure.

I'd be tempted to say it was due to different circuitry being employed in the pre-amp, rather than being down to polarity issues .... except that on about 10% of CDs, the non-inverted setting gives the best imaging.

It's also far more apparent on CD than LP. :scratch:

I must confess that with other equipment I don't notice much difference. It's just the Krell pre that highlights it for some reason. But mayhap that's because the phase button on the Krell makes it so easy to change. :bulb: Yup, that could well be it! :)

Phase issue is something that I studied in detail when I was doing my research for a "better DAC sound" over the last three years. I discovered that the main accepted digital filters that are designed to produce the high frequency roll off above 20KHz were a major cause of woolly bass and skinny treble. By just removing the feedback filter capacitor in the MFB filter circuit, or by adjusting the value of that cap, I could generate a wide range of phase shifts in the sound.
What Jerry noticed between digital and TT reproduction is due to the above. In the RIAA spec the phase shift is known from the RIAA correction curve. But in the case of the output circuitry of a DAC there is no accepted standard other than the recommendation that the signal is rolled off above 20KHz. So wide variations exist.

Are there any phase shifts introduced in the A-D process in the first place?

I haven't seen any filtering circuit in the analogue part of any of the A to D that I have on file from the chip manufacturers. But if one is inserted you would get an even bigger phase shift since you would be adding a double entry of a brick wall filter.

Do we know whether keeping phase integrity throughout is the ideal, or do you think that by simply correcting it right at the the end of the chain you're solving the problem?

I'm struggling to get my point across a little here I hope someone can understand what I'm trying to say!

First you have to be able to hear the problem before you can say it exists in the signal that you are listening to at that moment in time.

Croft preamps are designed to phase-invert the signal, therefore in order for them to perform optimally, the Left and Right output terminals at the back of the partnering power amp (or speakers) must be swapped round.

There is a very clear audible difference when that arrangement is not so! ;)

Marco.

I used to use JBL L100-T speakers that inverted phase, so I always connected them reverse polarity from the amp and they sounded best that way.

More recently, I've been playing with Tellurium Q cables. Their primary goal is to make cables which preserve phase coherence across the audio band. My findings are ongoing and I am awaiting delivery of their Ultra Black speaker cables for evaluation, but so far their claims are upheld as the XLR cables are very good indeed.

OK here's my twopenneth, one of the problems I identified when I was a record producer was lack of absolute phase integrity. At the most basic level, when a drummer plays the kick drum it creates a pressure wave moving forward which is picked up by the mic and hving been recorded and played back, the reproduced sound should logically cause the speaker one to move forward. Sadly this is not always the case, at Village Way Recorders in Harrow, I was confused by the fact that the JBLs in the control room never gave as precise a feel as the much less well positioned Tannoys in the main studio. We swopped the monitors and the problem remained in the control room. After a lot of head scratching I realised that although the speakers were in phase with each other the absolute phase was 180 degrees out in the control room. Having corrected this, the room always sounded right after that. When I went to cut after that I always checked that the phase of the repro was correct. As we know that leading and trailing edges of transients are important in our perception of the reality of the reproduction, this would all make sense to me and phase and time domain correctness have always been paramount when specifying systems.

There is probably a significant difference between the 2 discussions here, absolute phase and phase shifts with frequency.
There are very, very few phase coherent speaker designs, so it is quite likely nobody on the forum has ever listened to phase coherent reproduction.
OTOH testing absolute phase is easy, and particularly trivial in the kit made by companies which believe it to be important, since they will have provided a phase reverse switch. Sometimes remote controllable, both my Goldmund and DeVialet remotes have a phase button, for example.

Whilst I do hear a difference (as in my previous post) I don't really understand why ...

At a midrange frequency of say 1000Hz the speaker driver is zinging backwards and forwards a thousand times a second.
Does it really matter if it's going inwards rather than outwards on each of those zings? There's 0.001 seconds difference ... :scratch:

Or have I lost the plot? :lol:

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?

Hmm. :hmm:

I'm not trying to be difficult, just trying to understand something that doesn't seem to me to be logical, even though I happily admit to hearing it!

It seems to me that even a transient like a drum kick (or a violin pizzicato, or whatever) is actually a very complex waveform, generated by the motion of an extended diaphragm (or taut wire), and would have a time extent far greater than 0.001 seconds (0.0001 seconds at 10KHz!!), and so such variations would be lost in the grand scheme of things. I doubt the ear can perceive differences down at that level. It just doesn't seem to be mechanically sensible! :scratch:

I'd sure like to know what is going on here! :)

By the time you're three metres away from the speaker, phase gets screwed up by the room interaction anyway, but in the bass, the difference can be quite large I've found...

Phase coherance in speaker cables? new one on me, since we're not talking rf or microwave frequencies here, just very low audio ones which a heavy enough gauge wore should conduct without alteration.. Sounds like snake-oil shiite to me, despite any subjective differences these wires may or may not have. Would love to read documented proof of the claims :)

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! :scratch:

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

I know Jerry, but there's NOTHING on the Tellurium website other than a suggestion of pre-programming (create a "problem" to market a fix for) and subjective comments. I'm sure these wires are very good, but for "Plush" to suggest that £285 or so is a "modestly priced cable" is madness in the extreme :lol:

Anyway, if you like them in comparison to the usual Mark Grant and cheaper recommendations on here, then that's fine, 'cos at least you've compared :)

Back to bass absolute phase, I hear quite a difference here, but of course, I'm not switching "just" the drive units over, since the crossovers aren't symmetrical (my bridged power amps are specified as balanced on their outputs when used this way though so supposedly shouldn't react)..

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Originally Posted by f1eng

There is probably a significant difference between the 2 discussions here, absolute phase and phase shifts with frequency.
There are very, very few phase coherent speaker designs, so it is quite likely nobody on the forum has ever listened to phase coherent reproduction.

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I have heard phase coherent speakers many times, in anechoic, domestic and studio locations and they always have a greater realism than speakers that are not phase coherent. Time and phase are, in my opinion, paramount in reproduction of audio.

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Originally Posted by PaulStewart

I have heard phase coherent speakers many times, in anechoic, domestic and studio locations and they always have a greater realism than speakers that are not phase coherent. Time and phase are, in my opinion, paramount in reproduction of audio.

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Hi Guys

Would you consider the VMPS (Veritone Minimum Phase Speakers) range of speakers as Phase Coherent?
Sometimes manfacturer terminology can be confusing.

Andy - SDDW

How about full range single driver speakers?

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Originally Posted by Ali Tait

How about full range single driver speakers?

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Unlikely. Single driver speakers are working in cone breakup "NXT" mode at medium and high frequencies.
As soon as you get cone breakup you lose phase coherence. Phase coherence is lost in pretty well all crossovers too.

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Originally Posted by PaulStewart

I have heard phase coherent speakers many times, in anechoic, domestic and studio locations and they always have a greater realism than speakers that are not phase coherent. Time and phase are, in my opinion, paramount in reproduction of audio.

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Very interesting indeed. Which speakers are these please? Do you know how the designer and manufacturer managed to achieve phase coherence? If you heard them in anechoic conditions you -are- perhaps the designer??

As an engineer who started off life in noise and vibration research transducers have always fascinated me, and with this hobby I find microphones, pickup cartridges (and all the vibrating paraphernalia they are bolted to) and speakers particularly interesting.

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Originally Posted by f1eng

Unlikely. Single driver speakers are working in cone breakup "NXT" mode at medium and high frequencies.
As soon as you get cone breakup you lose phase coherence. Phase coherence is lost in pretty well all crossovers too.

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So what about electrostatics then?

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Originally Posted by Ali Tait

So what about electrostatics then?

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In terms of phase accuracy (assuming you have a phase accurate recording, i.e. not mixed multi-track) planar drivers should be the most accurate, depending on design, and whether they have a crossover. So ribbons and electrostatics should be OK.
Most have other problems though :)

Yep, agreed. However in my experience statics have the most transparent sound of any speaker type. Wonder how much of this is due to phase coherence?

I recall adverts for a 4-way loudspeaker from a company called Orchid which claimed to be phase-coherent. Anyone remember that? It was mega money, about £20K.

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.

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Originally Posted by MartinT

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?

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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..

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Originally Posted by jandl100

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! :scratch:

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

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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:

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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.

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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!

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Originally Posted by nat8808

Are you in front of the drums or behind them?

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

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Originally Posted by nat8808

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!

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

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

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? :scratch: ... Hmm ...

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!

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.

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.....

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Originally Posted by 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.

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

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Originally Posted by PaulStewart

*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.....

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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.