This is the email I recieved (without edit except for the name as I did not ask his permission to post here.) The engineer was responding to questions, which he repeats, from another member of the Harbeth user's site.
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m2 yip asks:
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Does/did the BBC often use this method (Blumlein) for their recordings?
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Historically yes, but (sadly in my view) less so now. I left the BBC in 1988, after spending 20 years there, latterly engineering lots of "classical" music in my part of the country. I often used to compare the BBC with EMI ... Blumlein's employers ... since they were both large British organisations with a long tradition of research and development of equipment and techniques. It used to be expected that all BBC classical broadcasts would be based upon coincident mics, though it was normal for additional "spot" mics to be used at times ... to optimise the balance in non-ideal situations. In recent years, there's been a tendancy to rely upon slightly-spaced omnidirectional mics as the main pair in any BBC "minimalist" balance. Some would argue that this gives a warmer ambience to the sound. I prefer to describe it as the pendulum of fashion swinging away from purity in the direction of "doing something different". Imaging and mono compatibility can most definitely be com!
promised (see later). With a few notable exceptions, commercial recording companies have tended to use non-coincident techniques for many years. One thinks of the "Decca Tree" of three omnidirectional mics, for example. I recently worked with a veteran commercial producer who said he'd never worked with a stereo mic before! Frankly, I've never liked these alternative methods. Neither did the celebrated audio pundit Angus McKenzie. I was once at a meeting where he said he'd "much rather listen to the average BBC recording than most of the b***** rubbish you get on gramophone records!". That was a few years ago!!
"Pop" and other musical genres are, of course, quite different, and place little or no reliance upon natural acoustics ... or on stereo positioning derived by purely acoustic means.
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What are the pros and cons of this method
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Practical cons:
Everything has to be "just right" for it to work properly. There has to be one "sweet spot" for the microphone(s) where the internal balance, the image width and the ratio between direct and ambient sound are all correct. Finding this spot and experimenting with microphone angle and polar diagrams all take time and effort ... especially if the recording venue is unfamiliar ... and both these are often in short supply. It may also be impossible to achieve the ideal position without encountering secondary problems. E.g. it might be very close to an audience, or perhaps there may be no easy way to mount the the mics physically ... or they might impede TV camera shots. And there may be other difficulties, like noise in the venue, which have to be considered.
Acoustic cons:
The necessary use of directional mics can sometimes impair the bass response. A little equalisation can help, as can the use of an omni "M" mic in an M/S pair. This equates to a coincident pair of back-to-back cardioid mics, and gives image width quite similar to that from a pair of figure-of-8s crossed at 90 degrees (the classic Blumlein configuration). Incidentally, the omni + fig 8 technique is the basis of many Nimbus recordings ... although they utilise an additional front-back "S" microphone and encode everything via a UHJ matrix for ambisonic reproduction, meaning that their recordings are not pure "two channel stereo" as generally understood.
Pros:
In my view, the outstanding pro is that natural internal balance and stereo imaging are superb. Some engineers and producers dislike having pinpoint positional accuracy ... they apparently find it distracting! But I feel very strongly that stereo ("solid") sound should be just that. In any case, such accurate positioning can be appreciated only by sitting in the optimum place between the speakers, so anybody who prefers not to hear it like that can sit elsewhere! Please leave the option open for the rest of us! What's the point of having speakers that are superbly matched for stereo (like any Harbeths) when the
image of the source material is patently inferior? On the whole, TV directors don't give us out-of-focus pictures so why should sound people be different? I have a couple of modern orchestral CDs (recorded by a well known, and highly respected, engineer) in which, despite the excellent tonal balance and superficially pleasant sound, the stereo imaging is truly awful. There are broad pools of sound around both loudspeakers, but the centre is totally un-focussed ... like a picture taken by a camera with dirt on the middle of the lens. In short, the recordings have "spaced mics" writ large all over them.
Harbeth speakers have an historic BBC lineage, and I don't think it's a coincidence that they clearly show up the differences between good and indifferent stereo imaging. Balancers who want the "warm, spacious ambient" sound could do worse than add a couple of more distant microphones to a basically Blumlein recording. At least the fundamental accuracy of the stereo image would be present in the first place.
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There must be thousands of Blumlein or other coincidental recordings in the BBC archives surely?
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Yes ... especially the older ones. Early EMI stereo recordings were the same. But let me finish with a true story:
A few years ago, I recorded a major television concert in Symphony Hall, Birmingham ... widely regarded as having outstanding acoustics ... and had to share the microphones of the BBC balancer who was already working there for radio. I was astonished to hear what
the mics were producing. None was positioned to pick up a "basic" overall sound, and the few that weren't unpleasantly close were so far away as to be unusable. The radio balance was available to my loudspeakers for reference purposes, and was puzzled how the other guy
managed to achieve a low-frequency bloom that I simply couldn't produce by manipulating any combination of his microphones. Half way through rehearsals, I went to his van and asked what the secret was. He pointed to a very expensive Lexicon reverberation unit! "I love the control all this gives me" he said! What price the superb hall acoustics and Sir Simon's internal balance?!! What price honesty? As we parted, I thanked the (young!) man for his co-operation and remarked "No offence, but next time I'll hang-up my own Blumlein pair". "Fine" he replied. "There's no accounting for taste ....... "
My feeling precisely!
Happy listening.
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