Steve_Graham@ub.cc.umich.edu (10/26/90)
Writing about Mercury Living Presence recordings, William Spencer asked: > Would someone like to explain exactly how 3 mikes are used for stereo? > What kind of mikes? Spread? Etc. So... There are many ways to produce a stereophonic recording, but they generally fall into one or the other of two classes: Spaced or Coincident. With coincident systems a pair of directional mikes (that is, mikes which produce a stronger signal for sounds coming from some directions than others) are mounted as close together as is physically possible. They are angled away from each other, and the stereophonic effect is produced entirely by differences in loudness: sounds from the left are picked up more strongly in the mike that points left, and vice versa. This "single point" pickup gives very precise left-right localization, but to some ears (mine, for instance) lacks depth. With spaced mikes a new element is introduced: time of arrival. Usually omnidirection mikes (which are in theory equaly sensitive to sounds coming from all directions) are used. Since the mikes are spaced apart, some instruments will be heard louder in one mike, and some in the other; but more importantly, sounds from the left will reach the left mike first, and sounds from the right will reach the right mike first. Our hearing system uses these time of arrival differences to establish location; a sound heard first in the left ear will be heard as coming from the left. So with spaced mikes much of the stereophony comes from timing information. One problem which arises is that if the mikes are spaced only a short distance apart then virtually all of the stereo effect is from timing, as both mikes will "hear" all the instruments with almost equal loudness, and because of the way speakers work in a room this may lead to some aural confusion. If the mikes can be moved farther apart the left-right separation will be more apparent, and at the same time it may be possible to locate the mikes for greater string presence, for instance. On the other hand if the mikes are spaced more than two or three feet apart the imaging will be rather unstable: Sounds which are only a little off center will appear to be all the way to the side, giving rise to the infamous "hole in the middle" effect. Some of these problems could be overcome by using directional microphones; the ORTF technique, which uses a closely-spaced directional pair of mikes, combines (to a degree) the advantages of spaced and coincident mike techniques. However, along with other factors, it must be remembered that in the 50's omnidirectional mikes gave the highest fidelity pickup, overall. And so to fill in the "hole" and give a more balanced stereo presentation of the orchestra a third mike was added, in between the left and right mikes. (The distance between left and right mikes can vary widely, depending on the engineer or producer's preferences.) This classic three-mike system is still in use today by Telarc, though they mix the three mikes directly to two tracks, and sometimes mix in supplemental mikes as well. The technique can provide good orchestral presence, spaciousness and depth, and an excellent sense of the hall in which the performance takes place. If balanced with the necessary care, the instruments seem to be spread fairly evenly between the speakers, rather than just at left, right, and center. In the early days of stereo triple-track tape-decks were used in the USA for a number of reasons. There were those who proposed actually using three channels to reproduce stereo: Left, Right and Center; the idea being that images from the center would be more stable, but sounds from the left and right would remain fully separated. (Some people still think this is a good idea.) At the same time, record companies were pretty quick to realize that given three tracks they could put, say, stereo orchestra on two tracks and use the third for the singer, and then would be able to fine-tune the balance between the singer and the orchestra after the musicians had gone home, or even redo the singer's track altogether, without having to have the orchestra hang around (and get paid). Alternatively, various microphones could be fed to the three tracks to enable the balances within the orchestra to be varied later on. RCA used the tracks in this way, for instance. Another way to use the three-tracks is to set up simultaneous two-channel stereo and single-channel mono balances on the same tape, so that only one editing session would be required for both stereo and mono releases. I believe Mercury used the three tracks for a combination of reasons: They hung three microphones in the "classic" spaced array (left-center-right), feeding each mike to one track on the tape. If I'm not mistaken they used only the center mike for the mono records, but used all three for stereo. I think they were hoping (initially at least) that real three-channel stereo would become viable in the home. But in the meantime the three tracks were mixed down to two in such a way as would give similar results to three-channel stereo, over the two available channels; that is, the left and right mikes fed the left and right channels, and the center mike was mixed equally into left and right, so that if it were heard by itself it would produce a "phantom" image between the left and right speakers. Whatever the rationale, it seems to have worked. --Steve Graham: sg2@ub.cc.umich.edu otherwise: USERHEFX@UMICHIB.BITNET
chrisc%gold.gvg.tek.com@RELAY.CS.NET (Chris Christensen) (10/29/90)
I have used a three mic or a Triad as it is sometimes refered to,
to record a 50 piece orchestra over the past five years. I have found
that the imaging is excellent. I don't agree that there is a lack of
depth. The recordings that I have done have included a 100 voice chorus and it is easy to locate the chorus which is behind the orchestra and on
risers. During one set up I was listening on the headphones after the
conductor had excused everyone and I was startled by a conversation
between two chorus members.
I have also sucessfully used the same setup to amplify the same
orchestra in an outdoor venu. We also put up our normal section mics
just incase the triad didn't give us the necessary gain margins.
The center mic is panned center and mixed in just to balance the
viloas with the violins. This minimalistic has proved to be a
very pleasing method of recording and reinforcment.
jas@proteon.com (John A. Shriver) (10/31/90)
Another argument in favor of intensity miking over directional, especially with 1950's microphones, is that the omnidirectional microphones were much flatter and less colored. The off-axis response of a cardiod or figure-8 microphone might not be all that flat. I guess one could also argue that an omni mike is less complicated, and might be less distorted (like the triode/pentode issue in power tubes). I don't know how much this argument holds with today's mikes. Mercury did separate mono and stereo miking setups from 1955 to about 1962. They note as much on the older album covers. The stereo tape mixed as mono would not have anywhere near the right level of reverberant information. Since they recorded about 80 stereo sessions before they could sell any stereo LP's, they certainly would want the mono records to be at their best. (I don't think the stereo 7-1/2 ips tapes provided any signifigant revenue, although the 1/2 track ones are sonically stunning.) Thus they recorded separate mono masters, so the mono would be at its best, since only it provided immediate income. They also used separate mono setups becuase they did not initially have enough 201 microphones to record mono and stereo simultaneously (including a spare 201). Thus, they used a 201 for the mono, and KM-56's for stereo. Anyone who wants to hear how important the microphone is can compare some of the monos to the early stereos. The best examples I can think of are Kodaly's Hary Janos Suite (MG50132/SR90132 & CD) and Bartok's Violin Concerto (MG50134[?]/SR90003). (If you have the stereo, the mono should be easy to find.) In both of these recordings, only the mono tape used the 201 mike. The differences are enormous, the 201 mike is much more immediate and clear. The stereo Hary Janos is still good enough to compete, but I'd argue that the mono Bartok is clearly the better recording. The mono records were also cut with a less fragile disk cutter, and are cut louder and more dynamic. The last drum roll at the end of the mono Hary Janos is a cartridge-buster! However, in later stereo materings the sound of the stereo cutter improved, a RFR-1 mastering of Hary Janos is brighter and more dynamic than a FR-3 mastering. Collecting all the mono Mercuries is a new challenge for the compulsive who already has a complete set of the stereo ones. They are much cheaper. Before the CD's they were the only affordable alternative. I have bought monos for $3.99 to listen to the performance and music, the better to judge how much I was willing to pay for a stereo. This allowed me to know I wasn't missing much (musically) when I passed on the stereo "Fiesta in Hi-Fi" for $125.
jdhill@BBN.COM (Jack D. Hill) (11/01/90)
In article <7333@uwm.edu> jas@proteon.com (John A. Shriver) writes: >The best examples I can think of are Kodaly's Hary Janos Suite >(MG50132/SR90132 & CD) and Bartok's Violin Concerto >(MG50134[?]/SR90003). (If you have the stereo, the mono should be >easy to find.) In both of these recordings, only the mono tape used >the 201 mike. The differences are enormous, the 201 mike is much more >immediate and clear. The stereo Hary Janos is still good enough to >compete, but I'd argue that the mono Bartok is clearly the better >recording. How right you are. I had a copy of the Bartok and for a mono I thought the sound was pretty good. So finally I decided to spring for the stereo version. When I finally found a copy and bought it I was very disappointed in the sound. The mono had much more depth, better frequency extremes and better dynamics. Luckily I was able to trade it back for a different Mercury, the Debussy/Ravel disk of Petite Suite, Tombeau... , etc. (SR 90213). While we're on the subject, why does the Kodaly Music Hungarica (SR 90179) sound almost like it's a mono? The other recording that I have with the same conductor and orchestra (and I assume in the same hall), Respighi Ancient Airs and Dances (SR 90199) sounds much more spacious. Does the recording sound better on CD? I am also curious about pressings. What is the general consensus on the following pressings that I've seen in my collection? 1. FR-? 2. RFR-? 3. SR 90xxx M 4. White labels 5. Vendor pressings 6. Orange labels 7. Mercury Wing (I have both M and RFR pressings) 8. Oval pressings 9. Different shades of purple labels I'm new to collecting Mercurys and I would like to get more information to help in my purchases. Thanks, Jack