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Everest gave a well-researched comparison of several design
for music recordings.
After 1990 or so, although professional recording engi-
neers had reached a consensus regarding the characteristics of a good mixing room, fewer and fewer such rooms were being built. The Pro Tools digital work station had become the accepted standard for tracking, processing, and mixing recorded music. Almost every music composer and produc- er acquired a Pro Tools setup and proceeded to use it in the nearest convenient location. A spare bedroom became a professional music production room. If we include music composed for television and movies, the bulk of music pro- duced in the U.S. today probably comes from residential studios. A major challenge for studio designers is how to make a small room acoustically acceptable for stereo moni- toring and mixing.
Control/Mix Rooms
As noted above, there is substantial agreement as to what constitutes a good mix room. It is a fairly large room because it must accomodate production personnel (or key- board players) in addition to the recording engineer. Two or three large loudspeakers are usually flushed into the front wall. The edge of the mixing console is about 7 feet from the wall, such that the distance from the engineer’s ears to the speakers is around 8 feet. A low cabinet behind the engi- neer’s chair holds a variety of electronic processing gear and also serves as a producer’s desk, with space for chairs at the rear. All these functional requirements add up to a room length of about 24 feet.
The room will be used at very high sound levels, and leakage into adjoining spaces is difficult to control, especial- ly at low frequencies. Background noise should be held to NC-25 or less, which may require placing computers and other noisy equipment in an adjacent closet or machine room.
The generic mix room shown by Eargle5 is 17 feet wide at the front, 22 feet wide at the rear, and 24 feet front-to- back. The ceiling height rises from 9 feet at the front to 11 or 12 feet at the rear. The room is acoustically neutral, with a scattered mix of absorptive and reflective surfaces. Eargle does not specify a preferred reverberation time, but expects the engineer to hear an equal mix of direct and reflected sound from the main loudspeakers. Working backward from that requirement, the corresponding reverberation time is about 0.3 second, and roughly half of the interior surface area must be absorptive. Dolby and THX standards for mixing cinema or TV sound in a room of this volume require a reverberation time of 0.25 to 0.3 second, so it seems that a room optimized for 2-channel stereo mixing should also be acceptable for surround sound mixing. An informal survey of West Coast recording engineers sup- ports that conclusion.
In fact, bilateral symmetry and the control of early later- al reflections are more important for 2-channel stereo than surround sound. Good stereo imaging requires a pair of well- behaved, closely matched loudspeakers, but if early reflec- tions are suppressed then the listener must be exactly cen- tered between the two speakers. Moreover, because each ear
approaches in the 1987 Handbook for Sound Engineers.
2
One of them generated enough interest and controversy to
deserve a brief discussion here.
In 1980, Don Davis and Chips Davis (the two authors are
not related) published a paper titled, “The LEDE Concept for the Control of Acoustic and Psychoacoustic Parameters in Recording Control Rooms.”3 The LEDE (live-end-dead-end) concept suppresses first-order reflections in the range from 0 to at least 5 milliseconds. Later reflections are made as dense and diffuse as possible. To achieve this goal in a control room of practical dimensions, the front half of the room must be almost completely absorptive, and the rear half must consist of reflective scattering surfaces. The design was said to pro- vide two important advantages. First, it tried to avoid comb filtering generated by early reflections. Second, the dense, later arriving reflections were intended to create the subjec- tive effect of a much larger room.
Regardless of the pros and cons of LEDE theory, it is dif-
ficult to implement in practice because the “dead” surfaces
should be fully effective down into the 200 Hz region. A
number of very small LEDE rooms were built, and they
sounded just as bad as other too-small control rooms. In any
case, although LEDE control rooms were actively promoted
for several years, they disappeared almost overnight, as did
other radical designs. In the following 30 years, much addi-
tional research was done regarding the role of early reflec-
tions and other aspects of listening room acoustics. The sub-
ject is fully covered in Toole’s Sound Reproduction, first pub-
4
grew rapidly, stimulated by the introduction of the digital CD as a universal playback medium. At the same time there was a steady shift away from large, multi-studio facilities owned by the major record labels. More and more albums were recorded in smaller independent studios. It became common practice to cut individual tracks in various venues, and then assemble the final product in a dedicated mix room. During that period the independent mastering engi- neer became an important figure in the production process, serving as a final retouch artist before an album was released.
After an unfortunate detour for quadraphonic monitor- ing, new control rooms in the U.S. gradually began to fit a common template, one that emphasized 2-channel playback but allowed for surround sound mixing as well. At the turn of the century the recording industry mistakenly assumed that consumers would rush to buy surround sound albums of their favorite artists. Things didn’t work out that way.
In the 2002 edition of the Handbook of Recording Engineering5 Eargle gives a description of a generic, high- quality control room. Its design will be taken up a little later, but one feature should be noted here. Eargle explains, “A center loudspeaker is often soffit mounted in the front along with the traditional large stereo loudspeakers, and this is to facilitate film work.” In other words, only three years after Sony’s introduction of the Super Audio Compact Disc, sur- round sound was not considered to be a successful format
lished in 2008.
In the 1980s and 1990s the music recording industry
16 Acoustics Today, April 2013