The Dorrough Vision

© Copyright 1997 by Dorrough Electronics

Recently, a number of "Dorrough clone" meters have entered the marketplace. While emulation may be a form of flattery, potential users should be aware that there is a danger of some possible confusion. The essence of the Dorrough Loudness Monitor is much more than a clever, multi-color LED display. The extensive research necessary to produce an entirely new concept in audio metering has resulted in a line of products unique in the world. We hope that this material will help you to understand the background and potential benefits of the Dorrough concept to your recording, studio or broadcast environment.

Introduction
It's basic human nature to use the established method of doing something rather than taking a philosophical approach and rethinking the basic concept of what it is one is about to do. In the world of audio engineering, this is no exception. The decades-old traditional approach of setting program levels based on analog meter movements has been deeply ingrained in our brains since childhood. So much, in fact, that the VU meter has become an icon for audio monitoring.

The reality of physics, however, is at odds with this simplistic notion that the sum total of a complex audio waveform, comprised of up to dozens of spectrally unique signals, can neatly be displayed on an electro-mechanical device closely related to the Boys Scout compass (a magetised needle floating on a leaf in a pool of water).

Fortunately, today's audio engineer is more enlightened. Engineering vocabularies now include staple terms like transient response, risetime, compression, spectral energy content, etc. Much of this increased awareness is due to the fact that today's audio and video transmission mediums are far more "technologically litigated" than ever. In short, our "father's VU meter" isn't relevant any more.

While experts argue the point about "VU" vs. "PPM", the most demanding recordists have already decided that neither is adequate for recording audio at the cusp of the millennium. Now, decades of research, and "in-the-trenches" experience have, at long last, determined a true relationship between RMS metering, integration time and peak-levels, finally delineating this Practical Standard. The advent of the Integrated Circuit offered an opportunity to apply this research to the creation of a compact metering device that could perceive sound "dimensionally". Many of the most prestigious media giants are already benefiting from a new generation of meters endowed with this "Practical Standard".

Historical Perspective
Even in today's more enlightened world of audio engineering, LEDs, Peak-Hold functions, combining VU and PPM into a single meter face, still fail to address the basic problem that both systems are based on old assumptions. Early audio engineers merely listened for "best results" and fashioned a meter display device to correlate with those desirable outcomes. By 1939 sufficient experience with these correlations produced the "Standard Calibration" or "Reference Level" sought through a joint effort by CBS, NBC and Bell Telephone Labs. It was apparent, right from the start, that the resulting audio metering devices still required interpretation by the audio technician.

Audio engineers, since the late 30's, used the "VU" meter as a basic yardstick of levels. Experience told them that what they were seeing on the gauge wasn't truly indicative of what they, or their recording devices, were hearing. Going strictly by the meter was only going to work if the recorded subject was a single, male-baritone, who spoke in a flat monotone! The instant an instrument, a female voice, background noise, or even emotion was added to the mix, the "VU" fell short.

Though some believe that the "PPM" standard came much later, it was favored in Europe at about the same time "VU" was being widely adopted in the United States. The PPM meter was the second solution. It didn't take long for users to realize that looking only at peaks could be just as deceptive as looking only at averages. A sharp repetitive, percussive sound could easily misdirect the engineer into cutting the overall levels back too far. The PPM meter featured ballistics with faster "integration time". This allowed transient peaks to be displayed without being unduly camouflaged by clipping or limiting devices. A slower release time was built-in to prevent the meter-needle from oscillating with certain "tempestuous" program material. All this conspired to make the PPM more accurate than the VU for certain applications but less attractive to those who wanted a meter that would better indicate fullness and actually "move with the sound".

 

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