This article is written by Christopher Huston, Senior Acoustical Engineer for Rives Audio. Chris is a recording engineer and producer with over 80 gold and platinum albums to his credit. He has recorded Led Zeppelin, the Who, Van Morrison, Pattie LaBelle and many many more. Chris has 30 years experience in studio and listening room design. His experience and insight into this subject are second to none.

The Soundstage: Home vs Studio Control Room
A couple of months ago, I was involved in a discussion about the differences between the acoustics in the home and those of the recording studio. The various responses to the thread, on the Rives Acoustic forum, were diverse and very interesting in that they underscored what an extremely subjective thing listening to music can be.

As a recording engineer and on more than a few occasions, I've been reminded of this subjectivity in some very amusing ways. For instance, one evening after a full day of mixing and on the way home, I was invited to visit some friends in the Hollywood Hills just to stop by and say hello. With me I had a cassette of the mix that I'd been working on. I asked if I could play it on their system, which consisted of Macintosh components and JBL speakers - a very nice system during the mid 1970s. As we sat on the couch facing the speakers, I was horrified! My mix sounded nothing like the well-defined track that I'd spent the better part of the day crafting in the studio. The bass was out of proportion, loud and boomy and the relative balances between the instruments and voices seemed way off from what I remembered from a hour before. I started to apologize, saying that it was just a rough, unfinished mix and that I was taking it home to evaluate - all of which was true. But my friend, a fine musician himself, waved me off saying that it sounded really great to him. He said that he knew his speakers and offered to put on some other records for comparison which we did.

Over the years since, I've learned that you can adapt to pretty much anything. That is, you can train your ears to get used to a certain pair of speakers and the room that they are in. This has proven useful because many of the professional studio control rooms that I've worked in all over the world leave much to be desired with respect to the sonic accuracy of their playback systems. I usually carry a few of my favorite CDs around to get a quick start on evaluating control room playback speakers.

There is a difference between the acoustic environment in which music is mixed and in which it is listened to for enjoyment. In a 1981 publication called "Studio Acoustics", Michael Rettinger gives a classic definition of the control room as a working environment: "Control rooms for music studios are for the purpose of regulating the quality of the recorded program rendered in the studio... The operations may involve level adjustment, the addition of a reverberatory note to the renditions, tonal modifications by means of equalizers, the use of limiting, compression or expansion of various passages and other checks and modifications..."

By contrast, the listening room is usually designed for no other purpose than leaning back in a comfortable chair and enjoying music. If I had to single out one area in which the relative differences were greatest between the control room and the listening room, it would be the soundstage. [It is important to note that the way in which Chris Huston is using this term 'soundstage' diverges from the usual audiophile custom - Ed.] Whenever we talk about the soundstage, we are talking about what can be a very complex and convoluted subject, one that can involve everything from the relative diffusion and reverberation time of a room as well as the interaction of its modes. Talking about diffusion and reverberation time might be explained by the fact that audiophiles invariably use the room as a creative part of their listening experience, certainly to a much greater extent than their counterparts, the recording engineers.

This is because the audiophile is seeking to add to his musical experience, enhancing and broadening the musical soundstage often beyond the intent of the original recording. The recording engineer -- or mixer as he or she is sometimes referred to -- tries to keep the musical soundstage within the confines of the information coming from the speakers, eliminating or at least desensitizing any acoustic artifacts that might artificially enhance or otherwise adversely color what he is listening to and evaluating. If the final playback room is providing the reverberation (and with it the illusion of depth) or any other complimentary aural quality, then the engineer might not feel that he has to introduce it himself on the encoding side by seriously affecting the final outcome of the mix. [As we shall see, this is the crux of the argument: Should the recording be as dry as possible since the playback environment will add its own ambience? Should the recording create its own deliberate ambience the way the engineer prefers it? Should then the playback environment be as dry as possible to minimize its own ambient contributions and let you hear the recorded ambience? - Ed.]

Reverberation and echo are used in the mixing of music primarily to separate instruments and vocals and to give an overall illusion of size and depth to the performance. Reverberation can then be used to make up for the recording techniques sometimes employed while making records. Studios are, for the most part, tightly controlled environments designed specifically to record instruments in close proximity to each other. Studio acoustics have changed drastically since the advent of multi-track recording. Studios were originally designed to compliment and acoustically enhance live performances of musical ensembles (groups, bands or orchestras), with their performance documented on either mono or stereo tape. Today, studios are more like workshops. Musical performances are no longer documented in toto by having all musicians play together in the same room. Rather, they are assembled instrument by instrument, track by track and piecemeal.

Commonly, instruments are initially recorded just for track-marking purposes to nail the structure of the song. They are replaced later with cuts where more concentration is paid on the actual performance.

The caveat to this is that in order to have control over the instruments and record them on separate tracks with as many musical options as possible, the studio acoustics must be controlled and therefore can be quite dead, sterile and lacking in kinetic energy (i.e. excitement). It is not hard to imagine the sound of one or two 100-watt guitar amplifiers, a bass amplifier and a full drum set all in the same room. If that room was live and without any acoustic treatment, the sound would most probably be uncontrollable albeit exciting, depending on your point of view. To counter this, many studios use iso (Isolation) rooms or individual smaller sound-proofed bays in which to place instrumentalists to ensure that they can be recorded with a high degree of acoustic isolation. During mixing, these deliberately separated instruments are recombined to make them sound as though they had performed together in a huge room without acoustic damping.

Having described the basic methodology behind the recording process as it is today, together with a few of the reasons for the controlled acoustic environment, let's look at what a soundstage is with respect to the control and listening rooms. In general terms, the soundstage might be said to be the area in which the listener sits and the speakers perform. This can extend to anything that has an acoustic influence or aural effect on that area. [As indicated before, this usage of the term 'soundstage' refers to the acoustic listening environment rather than just the virtual stage reproduced by the speakers as though the latter was independent from the former. - Ed.]

For instance, if the walls of the listening room are dead and without reflection and the floor is carpeted, the soundstage will be created predominantly by the sound of the speakers themselves. This will be particularly true at lower volumes where the room is not significantly involved in the reproduction of the lower frequencies because the various room modes (relative to the primary physical dimensions of the room) are not being excited and reinforced.

As the volume is increased, room modes can become major contributors to the low frequency response curve for good or bad. Thus far, this description is common to both the control room and the listening room. Now the relative philosophies part ways as the engineer and the listener require different soundstages. As mentioned above, the engineer does not want his soundstage to be overly live or reverberant. It could prevent him from hearing -- or interpreting correctly -- certain musical and aural nuances of the performance. The listener, in contrast, might want to literally create a stage.

The best acoustic soundstages to me are ambient but diffuse. Diffuse is the key word here. I want my early reflections to be spread out instead of being concentrated in one small area. Live areas that rely on singular or low multiples of acoustic reflections tend to have adverse and harsh coloration when compared to areas that have as their source multiple and closely spaced reflections that do not converge directly on any one listening position in the general playback zone. Small rooms tend to be harder to work with to create well-diffused soundstages. This is because the boundary walls of reflective surfaces are too close and easily activated by loud music. This is one of the main sources of adverse reflective coloration. One of the biggest victims of this type of reflective coloration is the human voice: Vocal intelligibility.

We've likely all been in halls, churches or rooms were the acoustics reduced voice intelligibility to zero. Churches are prime examples of environments that were designed primarily to enhance speech. However, as soon as sound reinforcement systems are powered up as has become the fashion, those beautiful acoustics are overpowered. Likewise, most older concert halls were designed to acoustically enhance orchestral performance and other unamplified events. It is interesting to note that the RT-60 (reverberation time) of certain concert halls has extensions of 1-2 seconds when measured in the critical bandwidth of the human voice (500Hz to 5Khz). Listening rooms and even studio control rooms can suffer the same fate if not enough attention is paid to their acoustical treatments. Although smaller than churches and concert halls, they are nevertheless bound by the same laws of Physics, just on a smaller scale.

One way to counter the closed-in effect of small rooms is to deaden the walls to stop the mid/high frequencies from reflecting. This is really a brute-force solution and not an altogether ideal or advisable approach. It is often used in smaller control room situations where a more controlled listening area/soundstage is preferred. It is also useful in certain smaller home listening rooms when more diffusive acoustic treatments are precluded because of room size or budge. The effect of diffusion as stated above is to produce multiple and closely spaced acoustic reflections which can, if correctly designed and implemented, enhance the listening area by adding dimension, excitement and kinetic energy to the musical soundstage.

Kinetic energy in an acoustic context can best be explained as follows: When low frequencies propagate in a room, they will eventually reach their physical potential which are the walls, ceiling and floor boundaries of the room. After striking these boundaries, much of the acoustic energy (depending on the construction of the room) is turned back into the room and proceeds to complete another full cycle relative to its wavelength until it naturally dies away after having expended its energy. As they move through the room, low frequencies are modulating the air, moving it around in complex patterns and forms. In this way, all the sound energy in the room is in constant flux which is sometimes referred to as kinetic energy. I like to think of it as musical excitement.

In a room that is too heavily damped, the low frequencies will be overly absorbed. This causes them to have less or no acoustic energy when they return from the room boundaries. This can cause the mid/high frequencies to travel in more or less straight lines through the room in what is basically unmodulated/unexcited air. The resultant sound can be harsh and unpleasant to the ear. The low-frequency characteristics of the room can thus act upon the soundstage e.g. the critical listening area. There is a myth about so-called bass traps. It says they should act so efficiently as to completely remove all room modes and cure all low frequency problems. This won't ever happen. The modal habits of sound in any environment are governed by Physics. The idea is not to remove all the bass from the room as this would kill all the energy and excitement of the sound. Rather, you want to allow the bass to reach its full physical potential naturally, without unduly loading up or exciting the room. You want the bass to compliment the musical performance rather than overpower it.

There is a school of thought that supports a different kind of soundstage, one that has the immediate area around the speakers dead and the area behind the listening position live. This LEDE concept was developed and championed by designer/acousticians Don and Carolyn Davis. LEDE stands for Live End/Dead End and was initially intended for studio control rooms. I first had a chance to mix in an LEDE control room in the mid 70s. The studio was one of four or five belonging to Wally Heider who, during the late 60s/early 70s, had far and away the hottest studios in both Los Angeles and San Francisco. Wally refurbished one of his control rooms and, wanting to stay on the cutting edge, incorporated the LEDE design into it. The studio did not get the rave reviews Wally had hoped for. In fact, just the opposite occurred. He quickly changed it back to a more conventional acoustic design.

The philosophy was to have the front of the room acoustically non-reflective (literally dead) and to rely on reflections generated by diffusive acoustic wooden arrays on the back (and sometimes, the rear side walls). I found it extremely hard to mix in this room and could not really get used to its feeling at all. In thinking it through, I realized that I didn't want to rely on reflected sound from behind me when listening to a stereo mix in front of me. Apart from feeling alien, I started to sense some potential pitfalls in the concept. For instance, while it might work quite well in a smaller control room, what would happen if the depth of the room was 25' or more? The sound would have to travel past me to the back wall and then be reflected back to my position at the recording console. This could equate to a round-trip distance of 37'. It is not hard to see how these reflected signals could really be in conflict with the original signal . At such distances, things are starting to become problematic. The signal path approaches becoming a discernable echo of the initial signal. This condition would be governed by the Haas Effect. It states that the human brain integrates all sounds into one if they arrive at the ear within a 35-50-millisecond window. Reflections arriving at the ear outside of this time window are being perceived as separate signals, i.e. echoes, reverberation or additions. This causes ear/brain confusion and loss of sonic clarity.

I hope that this short article has helped explain some of the differences between the control room and listening room environments and the reasoning behind them. Simply put, one is for creating a reproduction of the musical performances and the other is for enjoying them.

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