Among the spate of technical papers presented at the 63rd convention of the
Audio Engineering Society in Los Angeles was a provocative essay by Prof. J.
Robert Ashley of the Univ. of Colorado at Denver entitled "On the Degradation
of Symphonic Music Phonograph Recordings" (AES preprint 1513, A-2). Professor
Ashley is no stranger to the pages of Audio, and his involvement with loudspeaker
re search has led to consultancy and de sign work in this area with the Koss
Corp.
The essence of Prof. Ashley's paper is that he finds the majority of current phonograph recordings of symphonic music deplorably lacking in many of the sonic virtues that characterized the great recordings of yesteryear. He particularly criticizes the use of the newer concert halls for recording and the acoustic perspective presented through the recording technique of multi-track tape machines and multiple microphones. He points out that the mix-down of the multi-track tape to a two-channel master adds an extra quotient of distortion. He condemns the typical studio speaker used for monitoring on the recording sessions, as well as the use of cutting amplifiers with excessive amounts of transient intermodulation distortion. He feels that unless these current recording techniques are reversed or modified, they will negate many of the virtues of the impending digital recorders.
Prof. Ashley's solution to all this is, first and foremost, to record the sym phony orchestra in a great concert hall, use simple microphone techniques, eschew equalization and all other doctoring of the music signal, and use cut ting amplifiers with no audible TIM.
He singles out Carnegie Hall, Boston Symphony Hall, and some nineteenth century European halls as great recording halls, and ruefully he notes that "there are only a dozen or so of these great halls in the world." The professor has high regard for the early 1950s mono recordings of Toscanini in Carnegie Hall, and, in fact, he is particularly enamored of Carnegie Hall and its virtues as a recording hall.
Professor Ashley's observations are very timely, and in general I whole heartedly agree with what he has to say. However, with all due respect, the recording of symphonic music is far more complex, especially in the choice of recording venue, and the implementation of some of his ideas would be much more difficult than he may realize. Speaking as a recording engineer and producer of symphonic (more properly "classical") recordings, I want to particularly comment on re cording halls and certain other aspects of recording technique.
It is not, however, my intention to throw brickbats at recording engineers who use multi-track/multi-mike techniques for classical recordings. I don't like this technique, and I prefer to use microphones and a microphone methodology employing the least number of microphones which will ensure a true stereophonic recording.
Many of the engineers using the multi-mike approach are well aware of the compromises and shortcomings of this technique but are obliged to use it be cause of rigid company policy. I vividly remember the well-known director of a major record company telling me that he personally "prefers the simpler stereo microphoning techniques, but they are not commercial enough!"
How does a poor engineer cope with that?
Prime Acoustics
To me, the prime consideration in a classical music recording is the concert hall acoustics. Ideally, the hall should be large enough for the full expression of the most fortissimo music passages without overloading the hall, but not so large as to excite resonant and reflective modes that produce slap-back, flutter echo, and other acoustic anomalies. The reverberation period should fall within 1.7 to 2.2 S, and the decay should be smooth with no "shelving." The acoustics should lend warmth, airiness, and sonority to the instruments of the orchestra, but not so much that inner detail is obscured. Orchestral balances should be such that one section does not overwhelm another ...for example, trumpets and trombones should not acoustically "swamp" the first violins into inaudibility. Contrabassi and low percussion should have good projection, with solidity and weight, yet maintain good articulation.
There are very few concert halls, indeed, that can meet such demanding criteria as I have just described. A limited amount of correction can be accomplished by microphone techniques in halls with acoustic anomalies, but frankly, I'd rather not under take the recording if the hall is not first rate. Since there are so few really good concert halls in existence, many engineers, including myself, make a sort of hobby of ferreting out good recording locales in the various cities we visit.
I should hasten to also point out that a great concert hall is not necessarily a great recording hall. Especially with older halls, the prime goal of the architects was an attractive edifice where a considerable number of people could enjoy listening to a concert in relative comfort. Recording was virtually unknown, and, for that matter, so was the science of acoustics. A good concert hall was a matter of happenstance. Naturally, a given hall gained a reputation as a good concert hall when the sound of the orchestra pleased the large number of people seated in the audience. Of course, the acoustic response of a hall changes when it is empty, and some of the old great halls become too reverberant for recording when they are empty. In the best of all possible worlds, no one could fault Professor Ashley's formula for the successful recording of sym phonic music. But in the harsh realities of real-life symphonic recording, the recording engineer must cope with acoustic anomalies, which exist even in so-called good halls or, in many cases, admit the problems are insoluble, or worst of all ... make a good recording of an inferior hall.
Lore of Halls
Herewith, some lore about concert halls and symphonic recording locales that Prof. Ashley and you, dear reader, may find interesting:
Carnegie Hall, so beloved of Prof. Ashley, has been intermittently used for symphonic recording for many years, but has been on a steady de cline for this purpose for some time now. It has all the desirable qualities previously noted. When empty, the reverberation period is about 1.7 S, and the decay is quite smooth. Why then the decline? For one thing, the hall is incredibly busy, in use almost every day. If you are going to record there, it will have to be after midnight when you start or very early in the daylight hours. Since few symphonic recordings can be accomplished in one day, you would have to dismantle your re cording setup every day to make way for an evening concert, and reset the next day. The hall is also expensive in terms of rental and high fees for union stagehands who must move your re cording equipment in and out of the hall, plus handle setup and break down of the orchestra. The major problem, however, is that Carnegie Hall is noisy in terms of room rumble caused by the vibrations from heavy New York traffic and, worst of all, low and subsonic vibrations generated by the subway trains which pass underneath! Needless to say, many kinds of filters have been tried to cope with this noise, but most remove some of the extreme low-frequency content of the music as well, and this discourages their use. I well remember that just after the 1956 Hungarian uprising, maestro Antal Dorati conducted the refugee Philharmonica Hungarica orchestra in an evening concert in Carnegie Hall, and at midnight Bob Fine (of Mercury Records' "Olympian Series" fame) and I began to record the orchestra. We were armed with a sub way train schedule furnished by the city, and at that hour the trains ran 24 minutes apart. We stopped recording altogether during the passage of the trains, and this was some help in the rumble problem.
Changes and Improvements
One of the best recording venues in the Unites States once was Orchestra Hall in Chicago. This is where Fine made the first of the Mercury "Olympian Series" recordings with the Chicago Symphony, and he was the first to use the Telefunken U-47 microphone for this type of recording. While he was recording the orchestra mono phonically, I was simultaneously making experimental stereo recordings of the group with a pair of U-47s in the omni pattern. Orchestra Hall was simply luscious for recording, with a reverberation time of about 1.9 S when empty. In 1965, a wealthy patron of the Chicago Symphony gave money to remodel the hall, and, in addition to new seats and other improvements, they modified the curved proscenium that swept from the ceiling down to the back of the stage. In the original configuration, the stage did not form a "room within a room" as in most halls, but was open and largely responsible for the great recording acoustics. The remodeling caused a disastrous reduction in the reverberation time of the hall, to a much too dry 0.9 S. Because of this, all the companies that recorded the Chicago Symphony began to record them in the nearby Shriner's Medinah Temple. This is a largish hall with a very deep stage, and, depending on the engineers involved, some quite fine recordings have been made there. Some years later, Orchestra Hall was further modified, and the reverberation time rose to 1.4 S ... better, but still lacking. Now, it is well known that symphony orchestra players generally like to perform in their "home" hall and, if at all possible, record in it as well. Just recently, Deutsche Grammophon, who regularly record in the Chicago Symphony, tried a unique experiment. Wanting to satisfy the Chicago musicians, they spread heavy-gauge vinyl sheeting over all the seats in the hall. The seats, because of their upholstery, represented a considerable amount of acoustic absorption, and the vinyl sheeting reflected sufficient sound to lower the absorption in the hall and raise the reverberation time.
Thus, the musicians were able to record in Orchestra Hall once more, and although I understand they do not always use this setup, it is a step in the right direction.
After having told this encouraging story about trying to cope with marginal recording acoustics, here is the other side of the coin. . . .A well known record company, which re cords in a famous concert hall, uses multi-mike, close-up recording (up to 32 mikes!) to the extent that they swamp the natural acoustics of the hall and, in fact, are forced to add artificial reverb! So it takes all kinds, Prof. Ashley.
Your recording utopia will probably never be realized in the real world, but let us both hope the clinically revealing sound of digital recording may change all that!
(adapted from: Audio magazine, Dec. 1979; Bert Whyte)
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