Tech's Files: The Time and Space Continuum

Jun 1, 2009 12:00 PM, By Eddie Ciletti

UNDERSTANDING AUDIO PHASE AND POLARITY IN STUDIO ACOUSTICS

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There's a joke about a technician who, after years of retirement, gets called in to solve a problem that no one else has been able to repair. After inspecting the machine, the tech marks a small “x” in chalk to show where the problem is and then submits an invoice for $50,000. When the company demands an itemized accounting of the charges, the engineer responds, “One chalk mark: $1; knowing where to put it: $49,999.”

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Dedicated pros who invest a lifetime in their craft have a wealth of priceless knowledge. Nowhere is this more applicable than the elusive science (and art) of acoustics. A good acoustician can walk into a room and point out the most obvious errors without any diagnostic tools other than eyes, ears and experience. The on-site consultation fee from an acoustics expert can be money well spent.

Not all of us have the luxury of a well-designed workspace, and even “good” spaces should be re-evaluated from time to time. If that sounds like an invitation to go on a D.I.Y. journey for the terminally curious, welcome to this month's column, where I'll offer an overview of the most commonly used sonic diagnostic tools, plus a new dance: the oscilloscope twist.

In control room acoustics, one of the primary goals is to minimize reflections between the monitors and the listener. If all of the flat surfaces were mirrors — such as the desktop/console, sidewalls and ceiling — then reflections would be obvious, as would the optimum location for acoustic treatment. With mischief in the presence and “air” regions managed, “imaging” would be the most notable improvement — that is, the “realness” and depth of the phantom center image. Better acoustics translates into a more full-bodied center image. Analyzing and solving problems below 250 Hz can be more elusive, but let's start with the basics.

A-101

An acoustician's tool kit may seem impressive, but these tools are only as good as the user's ability to interpret them. Optimizing the control room environment may be unfamiliar territory as compared to the process of getting a good drum sound, but both applications share some common ground. The pre-DAW engineer's tool kit was “limited” to mic position, polarity reverse and EQ — all still valid. Sometimes, the either/or polarity option yields interesting and different results rather than a definitive “better,” and that's when workstations reveal themselves as more than just mixing and production tools.

Via DAW, the ability to freeze a moment in time allows for a greater understanding of how a single sound source arrives at multiple destinations — mics and ears — where the resulting combinations can make or break a recording, as well as your ability to monitor accurately. Now that we can zoom in on a multitrack drum recording, it becomes obvious that the 180-degree polarity-reverse option was, at best, a compromise.

We might not be able to time-travel, but using a DAW, time can be manipulated — from coarse sliding of individual tracks (in milliseconds or microseconds) to ticking off samples, “time aligning” by shifting the phase in degrees. It should also be noted that equalizers do their sonic sleight-of-hand by manipulating phase. An all-pass network like the Little Labs IBP Junior is a prime example of a tool that can improve the relationship between, say, a mic and a DI or an inside kick mic and an outside kick mic by allowing continuous 0 to 180-degree phase shift. This is great on a live gig where real time is essential.






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