Listening Tests and Absolute Phase

Editor's note: The subject of "Absolute Phase," more correctly called "Absolute Polarity," was of intense interest to audiophiles in the 1980s, culminating in the publication of Clark Johnsen's 1988 book The Wood Effect. I wrote an article on the subject for the November 1980 issue of English magazine Hi-Fi News & Record Review, which expanded on that subject to include some thoughts on audio reviews in general, thoughts that are just as relevant now as they were 37 years ago. It is reprinted here with the kind permission of Paul Miller, the editor of that magazine, now called just Hi-Fi News.—John Atkinson

The problem confronting the magazine reviewer when organising the necessary listening tests to accompany/reinforce the measured behavior of a device under test is complex. There has never been a problem with the measurement aspect; as long as someone has access to the same test gear—and full knowledge of the test conditions—then he should be able to replicate the critic's findings exactly (assuming an infinitely narrow spread of behaviour from sample to sample—a rasher assumption with some manufacturers' equipment than of others). However, when it comes to determining reliably the audible (or inaudible?) effects on music program by an amplifier/cartridge/loudspeaker etc. then the going gets tough.

Unlike the reaction of an oscilloscope, that of a listener involves interaction: what he is hearing; what he had been expecting to hear; the identity of the equipment; the emotional effect of the music program; the emotional effect of other competing stimuli (a recent cup of coffee, a not-so-recent visit to the toilet); the apparent expectations of his fellow listeners; the ultimate purpose of the test; the desire for self-consistency and hence self-esteem; all these can—but needn't always—color the listener's assessment. Obviously this will affect the reliability of any conclusion, both when used to predict the same listener's reaction to the same piece of equipment, and when used to predict other people's reactions.

Which brings us neatly back to the point of reviews, which ultimately is to enable a reader to decide whether the effect of a piece of equipment will or will not be beneficial, and if beneficial, more importantly whether the degree of any improvement is sufficient to justify the expenditure. Even if the reader has the necessary equipment and expertise/experience, the measurement-only review doesn't supply this information. It can still exist, of course, in isolation, but magazines don't enjoy a continued existence when only publishing information of no practical benefit to readers, no matter how elegant in its own right. Any audible effects of the measured imperfections have also to be communicated.

Thus there are two distinct processes involved: the determination (listening test results); and the resultant communication. The latter has been a much-abused area of journalism, perhaps because of the lack of a precise vocabulary to describe aural sensations. Adjectives drawn in from all aspects of human behaviour have been pressed into service when describing the sound of hi-fi equipment—a "velvet sheen" to the midrange, a "suet pudding-like" bass, "metallic edge to vocals," "green felt coloration" etc. Adrian Orlowski's recent article (footnote 1) was an attempt to define subjective terminology and perhaps Peter Moncrieff in the USA has gone farthest in providing a rational language to communicate subjective impressions. After all, to quote a recent contributor to the debate (footnote 2), "Should I be about to spend $2,000 on a Mark Levinson ML-1, I want to know about the clarity of the midrange, not whether its flavor is chocolate or vanilla."

More important, however, than the fact that the message can be garbled by the language used, is the validity of that message. As indicated, the reliability of a listening test can be seriously affected by a number of extraneous circumstances and a reviewer must exclude such extra stimuli. Without such care the test results will be randomised: any observable change must only be produced by the insertion of the test item into the chain, or otherwise no conclusion can be drawn. And even then, a major pitfall lies ready to ambush the unwary. If a change is reliably heard, how can any value-judgement be made without knowing what the program material should be like. As Peter Moncrieff put it when defining his "M rule" (footnote 3): "No evaluation of a device can be scientific if that evaluation is carried out through other devices that are imperfect."

A recent amplifier review (footnote 4) observed that as the amount of reverberation on some records appears to be less when using one amplifier than another, the first amplifier—a transistor design—must therefore be suppressing the ambience. But unless the ambience level on the recording is known, this can only remain one of a number of hypotheses. One could just as well say that the other amp—a valve design—was somehow adding ambience. In the actual review, this was ruled out as not being consistent with the author's apparent intrinsic belief that in a valve/transistor amp confrontation, faults should be attributed, if possible, to the transistor design. Carrying out any test non-blind ie, with the identity of the device under test known to be the listener, brings in all the above-mentioned additional stimuli, totally invalidating any conclusions drawn. The listener's capacity for self delusion so that he really does hear differences which are nonexistent in reality (but enjoy a healthy existence in the pages of magazines) when he is aware of the device being tested, I would say is practically infinite.

Scientific Method applied to equipment reviewing does not consist of setting up a test and drawing the conclusion which fits in best with the reviewer's preconceptions. Sadly, this is the way in which many published tests are performed, because when care is taken to remove all variables, bar one, the device under test, there is far less scope to wax lyrically in the true subjective-only review manner. How much more journalistic flair there is in writing that "the preamp made the music sound like it was being played by amateurs" to quote an infamous review of the Quad 33 preamplifier, than perhaps to say that there is an 0.75dB depression between 1 and 4kHz. Unfortunately, magazine sales show that the former style of writing appeals as much, if not more, to the layman. Similarly, the publicity-conscious Matti Otala saying that "We do not know anything about audio!" (footnote 5) sound much more impressive to the layman than would a dry technical argument—as in one of his many papers—as to which parameters contribute to what audible effect.

It is an unfortunate fact, however, that to produce a magazine review within the available money and time budgets, not all the variables can be eliminated totally. To apply the necessary rigorousness to satisfy a psychologist, say, would mean that a review might only appear after an overlong preparation period, which, in turn, would lead to the review appearing after the model had been made obsolete, particularly so with those from Japanese manufacturers. Happily, short cuts which only slightly compromise the review's reliability, derived from criticism of the performing arts, do exist. Use of a "transfer standard," to use reviewer Trevor Attewell's terminology, gives a "ground reference" to the subjective comments, and ensures repeatability of results while, in the first instance, copping out from absolute judgements. A record critic can compare a new performance against, say, a well-known Karajan one, secure in the knowledge that by doing so, the majority of his readers already familiar with the Karajan will be able to follow the reasoning behind his conclusions.

Absolute judgements, however, can only be made when the absolute program quality is known. With loudspeakers this can be effectively ensured by using self-recorded master-tapes, or with electronics, by using Peter Walker's straight-wire bypass (footnote 6) where the original state of the program material, before being processed by the device under test, is available at the flip of a switch.

Another shortcut, where reference to the "real thing" for practical reasons is not available, ie, with disc playing equipment, is to use experienced listeners who score the device under test as to how far it departs from their conception of "reality." Obviously, the magazine reader has to take that very much on trust, but with reliable listeners, work by Martin Colloms, Gordon King and Noel Keywood has shown good correlation between observed departures from the consensus panel opinion of "reality" and measured deficiencies in the device under test—using source material of known quality, of course. There is no point in judging an item on the way it handles stereo imagery, for instance, when using program not possessing coherent stereo information. Unfortunately many reviews in American magazines do do this, resulting, perhaps, in a "good" loudspeaker with a carefully and evenly controlled dispersion pattern—essential for good stereo when the listener is even a small lateral distance from the "stereo seat"—being downrated against a much poorer design with all manner of side lobes at different frequencies, which nevertheless, on non-coherent recordings of the spaced-omni type, can give a (program and frequency dependent) impression of "solidity." Moncrieff's "M-Rule" is once again being violated.

This is not to suggest that HFN/RR is overconservative, or even dogmatic, in its approach: to adopt an attitude of being certain that no differences between amplifiers should exist—as in the "bumblebees can't fly" proof—and thus examining listening test evidence on that basis, is as unscientific as ascribing every subjective difference "heard" in an imperfect test to the object of the investigation, ie, the device under test. Reviewer, magazine, and reader must be open-minded so that experimental evidence contradicting personal dogma, if shown not to be spurious, must be examined.

Absolute Phase
This rather lengthy preamble leads to the subject of absolute phase, for it was while trying to replicate reviewers' subjective tests data and discovering that as spurious causes for differences were removed—level differences, frequency response differences, awareness of device identity—so were the audible differences between amplifiers, by such means, Stanley Lipshitz of the University of Waterloo in Toronto, found that the polarity of signal absolute phase did matter. He wasn't trying to prove that differences between amplifiers were nonexistent, but, rather as a mathematician, as well as a hi-fi enthusiast, was applying a somewhat more rigorous scientific methodology to determine what the audible differences, described in absolute terms by the American underground press, actually were.

In early 1977, he had discovered that the slightly asymmetric waveform produced by the tone generator of the Wireless World Dolby-B noise-reduction kit sounded different with the device in "record" mode than when in "replay" (footnotes 7,8,9,10). The only circuitry change between the two modes was the insertion of an inverting unity-gain buffer on one but not the other. Level, distortion, and frequency response differences were all examined and found to be insignificant, so all that remained to explain the audible difference was the difference in phase polarity of the signal.



Footnote 1: "A Rational approach to subjective evaluation," Adrian Orlowski, HFN/RR April 1980 p.49.

Footnote 2: "Issues of reliability and validity on subjective audio equipment criticism," Larry Greenhill, Audio Amateur January 1979 p.17.

Footnote 3: "The M Rule," J. Peter Moncrieff International Audio Review 3, 1978 p.36.

Footnote 4: Michaelson & Austin TVA-1 amplifier review, Dave Berriman Practical Hi-fi, April 1979 p.99.

Footnote 5: Matti Otala interviewed by Basil Lane, Practical Hi-fi, March 1979 p.82.

Footnote 6: "Dynamic testing of audio amplifiers," Frank Jones HFN/RR, November 1970 p.1655.

Footnote 7: Letter to the Editor, Wireless World, May 1977 p.62.

Footnote 8: Letter to the Editor, Wireless World, October 1977 p.60.

Footnote 9: Letter to the Editor, HFN/RR, January 1979 p.81.

Footnote 10: "A little understood factor in A/B testing," S. P. Lipshitz, BAS Speaker March 1979.

ARTICLE CONTENTS

COMMENTS
Anton's picture

I am so old that I actually shopped for a preamp with the ability to switch absolute phase.

I grabbed a Krell KRC HR back in the day. Still a great piece of gear.

I can't recall the last time I read a review or saw a demo that still offered this feature or discussed this 'blast from the past!'

Maybe I haven't been looking.

Is it still a thing?

Herb Reichert's picture

...has a button to reverse phase

supamark's picture

makes good schiit (I've got a headphone amp and DAC from them, very happy with both).

Glotz's picture

This is exactly the type of material we need more online here. A wonderful dovetail to Jim Austin's Pass Labs coverage. Excellent piece, and love HiFi News.

PS Audio GCPH phono preamp has a phase switch, and it is handy from time to time... 10-year old product now, though.

(Dipolar) speakers (and their out-of-phase back wave) are also a 'variable' as JA wrote about in understanding phase and the effects of other components' system interactions. They are almost an infinite amount variables that affect a system, depending on complexity. Getting great sound is easy today, vs. decades ago, given greater component linearity in general.

"Carrying out any test non-blind ie, with the identity of the device under test known to be the listener, brings in all the above-mentioned additional stimuli, totally invalidating any conclusions drawn."
Read more at https://www.stereophile.com/content/listening-tests-and-absolute-phase#h...

Bingo! The answer to the age-old blind listening argument! The holy.. never mind. Yet more variables enter the picture, and begs the question- what is one truly listening for?

supamark's picture
Quote:

Yet more variables enter the picture, and begs the question- what is one truly listening for?

When you listen to music as a job, where you're mixing a lot of separate tracks down to 2 like a puzzle, making them sonically fit together with EQ, compression, and panning (a good arrangement makes your job so much easier), it's hard to turn that off when you're listening to music for pleasure. It took 10 to 15 years after I stopped working as an engineer to mostly turn off that analytical stuff.

Unfortunately, I'm still very good at hearing deep into a mix now that I've got my system set up properly again and a lot of crap still gets on my nerves. Example:

I like Queensryche's Operation: Mindcrime musically, but its lack of dynamics always kinda bothered me. I listened to Revolution Calling (track 3) for the first time in many years, with a modern DAC, and instantly figured out what had been bothering me - the mix engineer ran a compressor across the mix buss and screwed it up so when the snare hits the whole damn mix pumps down for a moment (incl. the snare) destroying the dynamics. I assume it was the mix engineer because Bob Ludwig mastered it and he knows how to properly use a compressor. The only other explaination I can think of is they used the same master to send to LP and CD plants in 1988 (it's an hour long, which doesn't really fit well on a single LP) but still, Bub Ludwig knows how to properly use a compressor and he mastered it (you can't really "undo" compression). Hearing it clearly made my ears hurt lol. Empire is a bit better in this regard, but sounds like they ran it through a BBE "sonic maximizer" unit.

Yes' Yessongs is the worst recording that I still love - the performances are so much better than studio albums but the sound is just... awful but I still wore out 2 LP's of it before I got it on CD. Little errors, like the bad edit in Pink Floyd's Another Brick in the Wall pt. 2 (it's that stutter in the drums at about 1:05 on the CD), amuse more than bother me thankfully.

All a long winded way of saying there's no telling what a person's preferences are. I mean, compare Art and Jason's (AD vs JVS) systems - it's obvious they value (very) different things in their playback systems but both bring their respective owners a lot of satisfaction.

Anton's picture

That was a fun post to read, Supamark!

supamark's picture

Some speakers wire one or more drivers out of phase.

Even in the 1990's, some pro audio mfgs wired their equipment with pin 3 hot instead of the AES standard pin 2 hot on their balanced connectors. In pop/rock, one or more tracks may have the phase reversed for any number of reasons (i.e., bottom snare mic to put it in phase with the mic on top).

Anton's picture

Sometimes this hobby feels like we are trying to turn hamburger back into steak.

As a side note: I always thought the speaker wiring schemes were to get 'in phase' arrival at the listening position based on how the drivers are set up. I may be way off, so I have no fact based assertion on that.

supamark's picture

it's mostly about x-over slopes (1st/2nd/etc order slopes) and how the drivers interact at the x-over point(s). Some slopes invert phase (2nd/4th), others don't (1st/3rd) from my understanding. Others can give you better answers.

DougM's picture

You realize you've now condemned us all to be furiously switching our speaker polarity back and forth with every record we play, trying to determine which sounds better. Time to buy more screw on banana plugs!

myrantz's picture

Interesting to see this article pop up (from 1980 no less). Have phase OCD ever since I mixed 2-Hot with 3-Hot gear. Before this did not even realise phase is even a thing.

Many audiophiles I visited have somehow managed to wire up their system incorrectly. They fall into these three categories:
1. Left/Right swap
2. One speaker out of phase
3. both speakers on inverted phase

3 was the most difficult to prove until a friend told me there is already a test: Speaker Pop Test.

Play that track, and run Studio Six's iPhone Speaker Polarity test. With this you can tell straight away if the system is + (IMO correct) or - (IMO incorrect). Or look at the cones, they should pop out (not get sucked in).

The problem is in hifi gear. Mixing EU and US gear is one cause. Another reason is some singled ended gear appears to be on - phase (e.g. I think one Conrad Johnson pre-amp owned by an audiophile I visited a few years back may be on -).

Music polarity is a lot harder to determine, as it's pretty much subjective and fatigue can set in quickly. To determine if the phase is inverted, I use cues like audio localisation, imaging and timbre. Last but not least, I use this totally subjective cue called 'emotional engagement'.

Some tracks which IMHO are on - phase:
1. Dark Side Of The Moon (30th SACD), e.g. Time and Money
2. Musik Wie Von Einem Anderen Stern Manger Test CD, e.g. Walking On The Moon and Jazz Variants

The tracks above sound weird IMO when played on a + system.

Those are the easy ones. Unfortunately a lot of music are often mixed with different phases, and sometimes Left and Right are swapped. Girl From Ipanema by Stan Getz is the classic example for me - I have 2 different CDs and 1 SACD. And still don't know which is the correct one - none seem correct.

Glotz's picture

Great info from everyone! Great to see insights from the pro recording world. Supamark's and Myrantz's comments are excellent examples.

myrantz's picture

Do you know why CJ gear are designed like so? That pre-amp has bugged me for ages and I never got to verify it.

John Atkinson's picture
myrantz wrote:
Do you know why CJ gear are designed like so?

Presumably to keep the number of amplification stages to the minimum. Unless used as a cathode follower, which doesn't have any voltage gain, a single tube stage inverts polarity.

John Atkinson
Editor, Stereophile

myrantz's picture

That's sticking to a 'keep it simple' policy and gotta say I love it. Hopefully in the future will have a chance to listen to a Conrad Johnson in + phase system and see how it really sounds.

Knowing this is like finally scratch out that itch. lol. This has bugged me for a while. Thanks guys.

spacehound's picture

That unlike us, who are enthusiasts with OCD about this sort of stuff, The record 'manufacturers' are sane people who don't care about phase (or anything much else as long as it sells) at all.

What's more, being professionals rather than bankers, brain surgeons or garbage collectors who falsely believe they know relevant 'HiFi' stuff, like we are, they KNOW absolute phase can't possibly make any difference to the MUSIC or voice, 'pop' test or not.

So their records have a 50-50 chance of the phase being 'wrong' or 'right' anyway.

supamark's picture

recording engineers are sooo much worse. I've spent literally hours listening to the same 30 to 60 seconds of a song on loop adjusting stuff and I'm hardly unique.

bpw's picture

Kudos for mentioning Clark Johnsen's book.

A quip by Keith Herron of Herron Audio some years ago at CES:
"We found out we were out of phase, so we ordered more."

Brian Walsh

ok's picture

Various phase shifts mostly at the high frequency range due to small inch-movements of the listener’s head – let alone room reflections – render absolute phase evaluation impossible in any meaningful sense through loudspeakers. I've switched "invert" countless times and never got nowhere. Anyway discerning absolute phase in blind A/B stereo tests seems as plausible as telling back/front page of any given A4 white paper. Listening to mono recordings through headphones while separately inverting each channel’s phase could arguably be a more sensible way for the brain to locate relative L-R phase shifts without interfering external cancelations (not as practical though, since hardware dissection possibly required..)

Timbo in Oz's picture

Because I don't like the imaging, and don't like the feel of things on my ears. And, my ears stick out, not flat to my head.

Hearing polarity on speakers is not impossible for me and many I know. Some can't hear it, ever.

Timbo in Oz's picture

A long time ago, in the early 1960s when I was still a 'tween, and a cathedral chorister under the Royal School of Church Music's scheme, our choirmaster/organist presented me with my leader's badge on its purple ribbon.

Privately he told me he believed I had perfect pitch, paused and said 'doesn't help much, does it?'. Equal temperament has been a good thing for most musicians, but I still wince.

Shrill sopranos which are VERY common, are a bete-noire of mine. Everyone else claps like mad!!!

I have been listening to phase and time coherent speakers for a very long time, and IME&O polarity does matter, but usually only on good (simply miked) recordings, some of which I have made myself.

(I've taken time out from that volunteer role, but hope to get back to it.)

We all do hear differently and are also differently affected by music, by the standards of playing and engineering. The assumption - built in to much of the argie-bargie about audio and testing - that we all hear and are affected by music, in the same way and to the same extent is false.

Bottom summed the reality up, in 'A Midsummer Night's Dream'.

For me, once polarity was shown to me, it became a chore to swap leads, and thus I had built two (L&R) spkr level switch boxes with two* DPDT relays. At the same time we took the HP-only xovers out of the 'spheres and put them in the boxes.

* I wanted to bi-amp the spheres. With two matching rethought LEAK St20s.

My wife hears polarity, too. Which helped with the budget.

I am slowly building a new system which will have similar relays to all the speakers, incluidng the four subs arrayed ala "swarm' ideas under & to the side of QUAD 63s in an arc.

A good way to test if you are right with polarity is to move as far to one side as possible. When the distant spkr is most clear that's the right setting.

For me the issue might well relate to timbre and expression, both of which depend most heavily on attacks and decays.

A good example here is the very different sound of tracker-action organs and electro-pneumatic organs. I was fortunate to hear this difference for several years, during those early 1960s, while our organ was being rebuilt.

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