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Four Audio Myths

Jun 6, 2011 2:51 PM, By Bob McCarthy

Misconceptions you need to know.

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3. You're overdriving the room

This is a close myth cousin to animated room acoustics. This myth goes: "The system was so loud that it overdrove the room." The idea is that the room got so full of sound that we could not fit any more in, or that the room acoustics reached a saturation point like the output tubes on a Marshall amp. While it is theoretically possible to get enough SPL to tear the air as a medium, you will need to get your sound system past the level of a Saturn IV rocket to get there. Even the most macho sound system does not have the power capability to significantly modify the acoustical properties of a room. If this were true, we would have meetings with the structural engineers to discuss how loud the system could go before the roof caved in.

Again, the saturation is in your head and (very probably) in your sound system—not the room. As level rises, distortion and compression increases in every link of the audio chain: amplifiers, speakers, the air, and our ears. The result is a reduction in the dynamic range—both real and perceived. Let's assume we have a sound system of unlimited power. Even so, the air, as a transmission medium, becomes increasingly nonlinear as we reach high SPLs. Extremely high SPLs encounter the elasticity limits of the air medium and the waveforms become distorted.

Once high-level sound makes it to our ears, it is a matter of time before our internal limiter, the tensor timpani, goes into action. The first peaks will get through, but then the eardrum's tiny muscle tightens and mechanically reduces the dynamic range of our aural system. Plenty of sound gets through to the inner ear, but the basilar membrane has mechanical and electrical (neurological saturation) limits as well. Increased distortion and compression are the products of overloading the receptive transducer system, just as they are with speakers and air on the transmission side.

Another of the aspects that leads to the perception of saturation is the extension of the perceived reverberation time (as described above). If we combine high level and fast tempo, the music can become a sonic soup where we lose the individual transient events. There is simply not enough time between the musical transients for the signal to decay enough to make room for the next arrival.

The importance here is in the assumption of responsibility. If a mix engineer mistakenly believes the room is saturated, the responsibility moves away from them. When we understand that saturation is in the limits of the air and in our heads, then the solution moves back into the mix engineer's court: Turn it down.

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