Well, of course, if you're using an MS pair, mono compatibility is flawless, unless you're also using spot mikes or, as you called them, touch up mikes, because when you combine the two channels to mono, the difference mike disappears. When Decca/London introduced "Phase-four stereo", it seems the main development was the pan-pot. RCA's "Stereo Action" releases were also a spotlight for the pan-pot. With the judicious use of spot mikes, the pan-pot should have solved the problem of image shifting.

When I was with CBC and whenever I was involved in training, I always emphasized that the main reason to insure mono compatibility is that good mono is a by-product of good stereo. Every sound in nature is audible to a one-eared person. But, naturally, there are innumerable opinions of what constitutes "good stereo". To me, good stereo results when the entire sound stage is percieved as a solid curtain of sound between the stereo speakers and with eyes closed, the speakers themselves do not seem to be the source of sound except for extreme left or right sound sources. To other engineers, the priority is the spacy sound that's produced when there's a large difference signal. This occurs with the fairly popular mike technique usually erroneously called "ORTF". I say "erroneously" because ORTF specifies precise measurements between mikes but most engineers I've seen apply the term to any near coincidental mike pickup.

db


On Saturday, August 30, 2014 3:19:09 PM, Tom Fine <[log in to unmask]> wrote:
 

>
>
>Hi Dave:
>
>Mercury experimented with 2-omni "binaural" and also with crossed-matrix single-source mic
>techniques. None were judged to produce the intimate yet spacial stereophony that 3-spaced-omni
>produced. Experiments were also tried with "touch-up" mics as were commonly used by RCA and Columbia
>and others. The problem there is that the image collapses and/or shifts when the whole orchestra
>goes full-tile vs. during quiet or section-solo times. This problem is called "congestion" by some
>audio reviewers and is very evident on 70s DGG and Philips recordings, to my ears, also Columbia
>many-mic extravaganzas. Decca made recordings with many mics (Mehta/LA "Planets" for instance) that
>don't get as "congested".
>
>It can't be understated how important mono compatibility was in the early stereo era. Stereo was a
>niche market, most of sales were mono, until the mid-60's when record stores stopped carrying mono
>versions of most new classical releases. For Mercury, the idea of having two mic setups ran counter
>to the compact and efficient production methods they had perfected. Same small team, same equipment,
>all the time. So, a big draw for 3-spaced-omni was also mono compatibility. The single-mic pickup
>perfected for mono became the center mic. No fold-down, no remix, no fuss. A mono full-track master,
>made from only the center mic, and a stereo 3-track master, both edited from the same edit notes,
>two LP masters cut. RCA for years used a separate mono setup and engineer. I think the same was true
>at Columbia. I don't know what 2-mic folks like Vanguard did for mono releases. You definitely can't
>successfully sum 2-omni stereo to mono. I think the Europeans who used MS or other crossed-matrix
>methods were able to use one channel for mono (although there were crosstalk phase-cancellation
>issues with that method).
>
>-- Tom Fine
>
>----- Original Message -----
>From: "DAVID BURNHAM" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Saturday, August 30, 2014 2:52 PM
>Subject: Re: [ARSCLIST] Accidental stereo (again)
>
>
>> Tom et al
>>
>> Very interesting posting, revealing some of the procedures and reasonings behind Mercury's mike
>> set-ups. I think some companies used two spaced omni pick-ups, (if I recall correctly, Capitol
>> Records had an inner sleeve with their stereo LPs describing a stereo procedure using 2 mikes),
>> but the 3 mike system makes infinitely more sense. As I think I've posted before, I used a
>> modification of the Mercury set up for my orchestral recordings - there were 3 omni mikes across
>> the front of the stage but the centre one was actually the mid portion of a C24 mid-side
>> configuration. The side mikes were C12s whenever they were available - the C 12 being a mono
>> version of the C24.
>>
>> I wouldn't say that Blumlein "invented" the 45/45 cutting method, I think he just put it forth as
>> a possible way of cutting a single groove stereo record. I don't know what, if anything, Blumlein
>> actually issued a patent for. Actually, since he was working for EMI, it's quite possible that
>> all of his developments were the property of that company and not his personally. Since it would
>> be fairly difficult to build a 45/45 cutter, I imagine that his experimental stereo discs were
>> likely cut using two separate recording heads - one starting at the edge of a disc and the other
>> starting about 3 inches closer to the centre.
>>
>> db
>>
>>
>> On Saturday, August 30, 2014 2:08:40 PM, Tom Fine <[log in to unmask]> wrote:
>>
>>
>>>
>>>
>>>I think it's a stretch to say that Blumlein alone "invented" 45/45 stereo cutting. Keller et al
>>>have
>>>US patents on it and Bell Labs successfully used it to make experimental recordings in the 1930s,
>>>among them with Stokowski/Philadelphia. As I understand it, those were 45/45 and not
>>>vertical-lateral stereo recordings.
>>>
>>>I do agree with your point about stereo mic'ing. Blumlein and Bell Labs came up with different
>>>approaches, and in fact Bell Labs experiements ended up favoring 3-channel stereophony as a more
>>>realistic reproduction of an orchestral sound source. The M-S and other crossed-matrix techniques
>>>were very firmly entrenched in Europe, to the point that people couldn't believe that 3 spaced
>>>omni's actually worked as well as they did for Mercury. Then a Philips engineering team tried the
>>>same technique in the mid-60's and got a series of very good-sounding recordings (somewhat
>>>un-Philips-like because they were both intimate and reverberant and not either-or).
>>>
>>>As for 45-45, as I understand it, the whole reason Westrex could charge a license fee for all
>>>stereo
>>>cuts, in the 60s and I think into the 70s, was because they inherited the WECO patents from Keller
>>>et al from the 30s. Again, if Blumlein had exclusively "invented" 45/45, Bell Labs wouldn't have
>>>been granted a U.S. patent.
>>>
>>>By the way, the theory of 3 spaced omnis is very different from 2-mic approaches. In the "M3"
>>>technique (as Philips called it), the center mic is paramount and is also the mono feed. The side
>>>mics are there more to add depth, width and height to the stereo image, not as much as primary
>>>sound-receivers (although they do perform this function for the side-most sound sources). The
>>>center
>>>mic must be focused perfectly of the image is diffuse. The side mics must be additive to the
>>>stereophony, as they are placed it becomes obvious where they are most additive (usually in a
>>>straight plane with the center mic). One of the reasons Mercury preferred having the mics on ropes
>>>vs. stands was that it was easier to move the sides at the same time (two guys on ropes). They
>>>used
>>>a surveyor's measure stick to record exact heights and tape measures to record exact distances
>>>from
>>>set points on the floor and walls.
>>>
>>>Few would argue that there is much less setup hassle -- but also less range of adjustment -- when
>>>using a single-point stereo setup like a stacked Blumlein array or a single-point MS mic like the
>>>AKG C24.
>>>
>>>-- Tom Fine
>>>
>>>
>>>----- Original Message -----
>>>From: "Paul Stamler" <[log in to unmask]>
>>>To: <[log in to unmask]>
>>>Sent: Saturday, August 30, 2014 1:19 PM
>>>Subject: Re: [ARSCLIST] Accidental stereo (again)
>>>
>>>
>>>> On 8/30/2014 5:37 AM, Michael Biel wrote:
>>>>> Because Blumlein was killed during WW II it is obvious that he was not
>>>>> the engineer who Keith Hardwicke was referring to. Besides, Blumlein
>>>>> was in research and development, not in record production or cutting.
>>>>> By the way, Blumlein was NOT the the one who discovered the art of
>>>>> stereo recording. Arthur C. Keller of Bell Labs was doing stereo
>>>>> recordings in the Capitol Theater in 1927, four years before Blumlein
>>>>> envisioned it. Keller did stereo recordings of Stoki and the Phila in
>>>>> 1931. the Brits have done a dandy promotional campaign for Blumlein
>>>>> which is why he is "credited by most" even if the "most" are wrong.
>>>>
>>>> But Keller and Blumlein were using very different recording techniques, so to say that either
>>>> discovered *the* art of stereo recording isn't accurate. Keller used spaced omni microphones,
>>>> while Blumlein used a pair of figure-8 microphones stacked on top of one another and pointing at
>>>> 90 degree angles to one another. The former technique creates the stereo soundfield from a
>>>> combination of intensity and phase differences, while the latter uses intensity differences
>>>> only.
>>>> Blumlein also developed the "45/45" techniquee of cutting a stereo signal into a single record
>>>> groove; it became the standard format in the 1950s when it was reinvented by American engineers
>>>> at
>>>> Western Electric.
>>>>
>>>> Peace,
>>>> Paul
>>>>
>>>>
>>>
>>>
>>>
>>
>>
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