The Stereo Image Page 2

This position is philosophically untenable: to involve the concepts of "accuracy" and "realism" must be fallacious when discussing just one component in the reproduction chain, because you then introduce another variable: the quality of program material. If you are to assess the imaging properties of a pair of loudspeakers using music program with subjective reference to the live experience, you must know how well the stereo aspect of that live experience has been preserved on your two information channels. But you only have access to that information by listening to the program on loudspeakers of unknown imaging properties. You have one too many variables—and a circular argument.

It is also untenable on more practical grounds. Let's look more closely at the problem of identifying sound-source location in the concert hall. As a regular concert-goer I am very much aware that my degree of confidence in aurally locating instrumental images varies enormously. It depends on the hall, on one's seat position, the presence of reflecting walls near the instrumentalists, the nature of the instruments themselves, and so on. Take London's Festival Hall. Sitting in the centre about halfway back, so that the orchestra subtends an angle of about 60°, one can accurately locate most instruments—apart from the horns, which have their bells pointing towards the rear wall.

As you move further back, however, two things happen. Firstly, the angle subtended by each instrument gets smaller, thus increasing the relative effect of any confusing element, and secondly, the ratio of reverberant to direct sound intensity increases. In the Festival Hall, as one moves back under the balcony there is a marked change and it becomes much harder to locate individual instruments with any confidence. The direct wavefront from the oboe, say, now only represents a very small fraction of the soundfield at your listening position, and it is not surprising that you can't be absolutely sure of the position of that oboe.

This is the situation described by Hirsch and many others. But consider the soundfield at that point more carefully. Your ears are still receiving a mass of directional information which is being interpreted unambiguously: although most of the sound impinging on your ears represents reverberation, your brain acts on those reflected wavefronts in exactly the same way that it does on direct wavefronts. This is how you know that you're sitting in the Festival Hall, near the back under the balcony, with a relatively narrow orchestra unambiguously in front of you. Your direction-finding apparatus is as accurate as ever, but by choosing to sit further back you've reduced the proportion of useable information concerning the individual instrumental positions; in effect, you reduce your brain's signal/noise ratio when you consider the orchestra alone.

But what does this relative lack of orchestral directional information have to do with loudspeakers? At a recent AES meeting on microphone techniques (see HFN/RR March 1981, p.37) Peter Baxandall put his finger on the crux of the whole business when he said that he preferred to sit so far back, because although the orchestral positioning accuracy was impaired the overall sound was better, being better integrated.

Choosing to sit that far back is purely a matter of personal taste. A loudspeaker which confuses the location and width of our infinitely narrow central double-mono image, and hence the locations of the whole lateral continuum of narrow images (exactly as if we had been removed several rows of seats further back in the Festival Hall) is a less good design in high fidelity terms because it is adding a distortion to the program. The fact that many would find the effect of that particular distortion more like the realism they prefer, regardless of what directional information was captured on the recording, is totally spurious.

The narrowness and stability of the central image at all frequencies, and the maintenance of that narrowness (within established psycho-acoustic limits) at all positions across the stereo stage as the L/R voltage ratio is altered, is the only certain indicator we can have of the absolute imaging properties of a loudspeaker. The fact that many records will sound less attractive to many people with such a loudspeaker can only be a criticism of the quality of the program.

Accuracy vs Musicality
Which brings us to the split becoming more and more apparent amongst enthusiasts and manufacturers alike. If most records sound less-and-less to your taste with every improvement to your system, then why bother with the whole business at all? Paul Benson, ex-Editor of Hi-Fi Answers, highlighted that particular point in a stimulating if controversial article last September. "The goal of a stereo system is to create, in the home, a musically satisfying performance" he wrote, and if the more pedantic critic will be upset by the notion that one's hi-fi might be creative as opposed to reproductive, it is surely true that unless possessed of masochistic tendencies one does basically want to enjoy the music on one's records.

Hence the appearance of loudspeaker systems which sacrifice the stereo aspect of performance to a greater or lesser degree, dependent on the acoustics of the listening room, in order to optimise other aspects. The Linn Isobarik, Sara, and Kan, Heybrook HB3 and ARC 101/202, are all designs which are intended to be stood against a wall to achieve their intended bass loading. However, the reflections from that wall follow the initial wavefront after so short an interval, around 2–3 ms, that the ear/brain tends to treat them as part of that wavefront, and as the level of such reflections will be dependent on frequency, the overall effect is unpredictable and results in a "smearing" of the imaging. In the worst case, I have heard a pair of Isobariks producing nothing more than a "fat mono" sound—it was instructive to note that the listening room in that case had seating everywhere except in the traditional central position.

The sound in that room was very "musical" and I enjoyed listening to many records on that system, but it was a relief to get back in front of a pair of Quad ESLs and relax in the security of their rock-solid stereo, even if this meant that on some orchestral records the violins, for example, sounded as if they had been crammed into a telephone box to the far left of the stage, balanced only by the cellos stuffed in another overcrowded box stage-right. Proponents of the B'rik sound would say that this represents "unrealistically good imaging" and I agree, arguing, however, that it was a program fault which the Quads, with their greater stereo resolving power, had allowed me first to identify and then to decide whether it was acceptable or not.

Ignorance may be bliss, but a uniformity of imaging—everything reduced to that "fat mono"—is ultimately tedious, and I can only conclude that it is the generally low standard and unrealistic quality of recorded stereo, with its fatiguing positioning anomalies, which has led people to put the ability to present accurate stereo a long way down their list of desirable loudspeaker qualities. Perhaps Dr. Amar Bose had a point after all—the fact that a violin image is presented as being 20' wide can be forgivable when the result is ultimately enjoyable rather than fatiguing. And yet, despite all this, listening via good headphones it widely agreed to be very satisfying because it is uncannily accurate in its presentation of the lateral stereo information!

To Recap
Given that the correct positional information is present as a succession of instantaneous voltage ratios in the two information channels, then all the loudspeaker pair has to do is to reproduce those voltage ratios as sound level ratios in order—ignoring room interaction effects—that a convincing soundstage be set up between and behind those speakers. The end of your listening room becomes a wide window into the acoustic of the recorded concert hall, with every instrument its correct size and in its correct position.

Correctly Capturing Directional Information
In the first part of this article I looked at what information needs to be recorded on just two information channels in order that an accurate stereo image can be reproduced by two loudspeakers. If we agree that with "accurate stereo," instrumental directions at the original event are preserved, then each of those directions only needs to be represented by a voltage ratio between the two channels. The sum of those two ratios, integrated with respect to time, represents the stereo image, and the human brain proves to be a wonderful instrument in that it can sort out and unmix the ratios from the two signal waveforms and identify individual instruments—with their appropriate directions—within the overall texture.

This is an amazing feat, the aural equivalent of defying the 2nd Law of Thermodynamics and unmixing two differently coloured liquids after they have been poured into one container. The best that machinery can do is exemplified by a new measuring instrument from Trio (Kenwood abroad), their model 5920 Sound Image Meter. This measures what Trio term the "interaural correlation coefficient"—IACC. A dummy-head stereo microphone "listens" to the stereo soundfield and the meter examines the signals perceived by the left and right "ears." Effectively, it compensates for the time delay around the head from ear-to-ear and then compares the resultant two waveforms. If they are identical, then both channels are carrying identical information and the IACC is +1, corresponding to a monophonic signal. If the signals are identical but 180° out of phase, then the IACC is –1, a negative correlation.

The use of this Trio meter is obvious: play monophonic white-noise through your two favourite speakers in your listening room, place the dummy-head in the "stereo-seat," and the departure of IACC from "+1" tells you now precise (or rather imprecise) a stereo image those speakers will produce. The effect on the stereo of nearby room boundaries, for instance, can be immediately assessed. (With typical speakers and a typical room, Trio say that the IACC will be between 0.2 and 0.8—the nearer to 1 the better.)


Bogolu Haranath's picture

"Last days of the century" or "The thrill is gone" or still running "Against the wind" :-) ..........

Bogolu Haranath's picture

Excellent article ........... Still trying to digest all the information .............. May be I have to read it couple of more times ..........

Bogolu Haranath's picture

If you are serious about audio, sound production and re-production, this is one of the "must read" articles ..........

dalethorn's picture

"With the advent of cheap domestic digital playback systems in the near future, the 'joins' in that montage will be all the more apparent, and thus at last the consumer will be able to put real pressure on the record companies." -- I suppose we did in fact put some commercial pressure on them, but instead of converging to a more realistic image, we've split into different camps with different philosophies. The joy of digital as it were.

And it's not like headphones have made things better, except perhaps in remastering older recordings. In remastering you see, it's like oldies radio - you aren't going to hear all the crap they played along with the "better" stuff back then - you have the advantage of hearing just the "better" recordings hand selected for those playlists. Unless of course you're streaming, where you have to wade through the umm, "lesser" material.

Bogolu Haranath's picture

In my opinion, modern headphones (and in-ear 'phones) are saving high-end audio ......... They are lot less expensive compared to the loudspeaker based systems and lot more portable ...........

Glotz's picture

This will helpful for a lot of neophytes wanting to learn more about sound perception and further hammers home the need for exacting controls when listening critically.

Everyone should read this twice.

hifiluver's picture

Yes, Good article. When I first started buying sound equipment I visited this dealer who chose certain recordings and place the speakers heavily toed in to create a '3d hanging in the air' presentation. I thought it was magical and something to be attained, only to realise 2 decades later that this type of 'sound' is illusory and non existent in the natural world. Attending concerts (even the most amateurish ones)live music, amplified or otherwise helped put a frame of reference around expectations the next time the credit card came out.

Allen Fant's picture


Excellent article with a plethora of information to digest.
Plus, a photo of a dashing JA.

Bogolu Haranath's picture

Young JA looks like one of the members of the young Beatles .......... Now he looks like one of the members of ZZ Top, may be? :-) .............

spacehound's picture

He was doing his Julian Vereker impersonation.

spacehound's picture

I think John made it up.

soundhound's picture

Great article, yet like all such articles there is little in-depth analysis of the MS technique. This technique seems to have so much going for it, yet I never hear of it being used for classical recording. Is there some drawback to its practical use?

Bogolu Haranath's picture

Also, "Decca tree" type of recording technique is not mentioned ..............

John Atkinson's picture
Bogolu Haranath wrote:
Also, "Decca tree" type of recording technique is not mentioned

The Decca Tree is an variant on the 3 spaced omnis technique. It's a spaced pair of omnis with a center fill mike placed forward of the other two, See I used it for Stereophile's Duet album: see

John Atkinson
Editor, Stereophile

Bogolu Haranath's picture

"#that POWER" :-) ...........

Bogolu Haranath's picture

Some audio reviewers have advocated for 3 front speakers (instead of 2) for accurate imagining, including depth perception ......... That may work well for "Decca Tree" type of recordings, with 3 channel audio (like SACD, Hi-rez audio Blue Ray etc.) ........... That 3 speaker placement could be problematic, if we listen to other types of music recordings like Pop/Rock etc., where the recordings are 2 channel ........... We constantly have to move the speakers, for listening to other types of music ..........

Bogolu Haranath's picture

To add to the above ............. I am glad JA talks about "binaural" recordings ........... Binaural recordings seems like, they are having a resurgence in recent years, because of the popularity of headphones and in-ear phones ....... Also, modern DAWs can be helpful to compensate for recording deficiencies ..........

hollowman's picture

With the hair style, beard, microphones ... all in the context of recording engineering ... one would swear an uncanny resemblance to....

Bogolu Haranath's picture

JA did make some great recordings for Stereophile ..........

Bogolu Haranath's picture

JA mentions about sitting far back in the concert hall, for integration of sound ............ If someone sits too far back, they could have problem hearing the soft passages ...........

dalethorn's picture

Many of my better recordings have such a dynamic range that my listening location can't accomodate them until 2-4 AM. I see DR numbers all over the place, but the loudest to softest sounds in my recordings (those that are necessary to hear) must be 30-40 db different.

Bogolu Haranath's picture

May be JA could come up with an updated modern version of this same topic, and publish it in Stereophile ........... This essay is almost 40 years old ............

dalethorn's picture

Given that it's "Stereo Image" and modern stereo recordings are more than 60 years old (25 years older than this article), what could possibly need updated?

Bogolu Haranath's picture

Some of the techniques like M/S type (as one of the readers mentioned) and "Decca Tree" are not mentioned in this article ............ Also, modern DAW processing/recording is not covered ............

Bogolu Haranath's picture

To add to the above ............ Some of the older recordings could be re-recorded (with new and different artists) and re-mastered .............

dalethorn's picture

And would any of those efforts to "remaster the catalog" bear any resemblance to a 3-letter acronym that begins with 'M'?

Bogolu Haranath's picture

Rubinstein Nocturnes is a good example of what re-mastering can do ........

dalethorn's picture

But how much personal effort went into remastering Rubinstein versus remastering Radka Toneff? If you read the story on the latter, you'd see that they made significant improvements that justified the purchase to anyone who was vaguely interested. If the effort to remaster Rubinstein is not especially greater than the average MQA remastering - even though there are "clearly audible improvements" as the sales pitch typically goes, then those things you mentioned as justification will raise a huge wall of cynicism in the audiophile community.

What I'm saying in effect is, the real goodies we get are generally unrelated to those "M/S type, Decca Tree, DAW etc." issues. Not to diminish those things - just saying where the priorities likely are.

dalethorn's picture

Clarification -- not diminishing the Rubinstein remaster either. It was likely a labour of love. Those other things are technical, and would be part of an automation process, like MQA.

Bogolu Haranath's picture

True, true, true ........... In addition to all of the above, Iso-Mike recording technique is not covered ........ This article is 40 years old and IMHO, needs to be updated ...........

dalethorn's picture

The problem is, the article is already too big and complex now, and too daunting for newbies to look into. If the article were to be expanded to cover the important newer recording techniques and other relevant discoveries, it would be extremely large and indigestible even by AES standards.

So who will pay to turn this into a college-level course, which it needs to be? The reason I ask is because colleges and their curriculum don't generally serve audiophilia.

Bogolu Haranath's picture

I am sure you, me and some others on this forum will read it ........... We are all "dedicated audiophiles", aren't we? :-) ............

dalethorn's picture

See, the problem is much bigger than you suggest. Let me give you a real-life example. Many people whine and complain about social issues in our society, of which audiophilia is just a part. And audiophilia is based on principles, not just a set of facts. Now in the larger world, when people are wont to disagree on nearly everything, they appoint representatives to arbitrate their differences. And still, many (millions) are not willing to compromise their principles in order to move forward on day-to-day issues, and so those (who will not compromise) cannot be part of the arbitration processes.

So if our principles are more absolute than society at large (I believe they are), and we intend to maintain those principles as we move forward on our education, discovery, and enrichment of our hobby, we will need strong leadership to make those moves. Not only that, but a very strong commitment to that leadership by the vast majority of audiophiles. Does that sound like a cult? I can't say ..... but what I can say is without it, we will drift along exactly as we are doing now, and the standards will be determined by the most successful players.

dalethorn's picture

For example, J. Gordon Holt. There are other names, but until someone can take up his position as the erstwhile godfather of audiophilia, we the audiophile sheep will remain scattered.

Bogolu Haranath's picture

JA and other reviewers at Streophile are strong (cult) leaders :-) .........

dalethorn's picture

Leaders - plural sense of leader. Multiple leaders, multiple opinions.

Bogolu Haranath's picture

Ok ...... Let us all make Bob Stuart (of MQA fame) as our fearless leader :-) .......... He can convince and influence anybody :-) ...........

dalethorn's picture

You wouldn't want a supreme leader who is divisive, now would you? And I'm not suggesting for a moment that Bob would want to be divisive, but ..... choose the wrong leader and there goes your hobby.

david-p's picture

"In particular, use of a coincident technique, with its capture of the acoustic in which the musicians are performing, necessarily implies that the acoustic should be both suitable for the kind of music and attractive in its own right. This is rarely the case and, although ideally recordings should only be made in one of the apparently small number of good venues, commercial realities mean that the convenient location of a hall and its facilities often outweigh its total lack of a good acoustic. Walthamstow Town Hall, and All Saints, Tooting, for instance, are often used, yet the excessive wash of reverberation in such places—when empty of an audience-makes the live orchestral sound strange indeed, and not a sound that one would particularly want to record at all. The conductor also has a problem in hearing all of the orchestra!"

I worked on EMI recordings in both these places during the 1970s. Tooting was a special case, though some excellent recordings were made there; but I would dispute the above description of Walthamstow Town Hall. The Giulini recording of Verdi's Don Carlos demonstrates this. It was done in Walthamstow and no difficulties were encountered in making an excellent recording.

Nearly all the recordings I make today have a fig 8 stereo pair (or in the case of surround recordings an WXY ambisonic mic) as their basis. The exceptions are recordings of organ and other keyboard instruments, and choirs, where it is undesirable to have the ability to locate the position of individual strings, pipes or singers. In my opinion, for these cases omnidirectional mics work better, giving a pleasant stereo spread, with the expected blend.

Regarding "suitable acoustic", mentioned above, unless one is just intent on making a record of a performance in an acoustic over which one has no control (e.g. concert recording), it seems to me that in this day and age, when we are not short of older recordings of excellent quality covering most of the "classical" repertoire, I do not understand why anyone would elect to try to make a studio recording in an "unsuitable acoustic".

As far as making this topic into a "college course" is concerned, I did this, though more than one semester is needed, and taught it with great success over more than 20 years in the UK and USA. Many of my former students are well-known successful engineers and producers.

DougM's picture

JA states that perceived image depth is a function of perceived reverberation, but I would argue that it's also a function of tonal balance, in that a more prominent midrange will make an instrument sound closer to the listener, and a recessed midrange will make it sound more distant.