| Aphex
Granted Patent for Unique Design of Low-noise Variable-gain Amplifier Used
in Ultra-precision Mic Pre-amp The patented invention, LeNA, is low noise and eliminates clicks, pops and "zipper" effect while adjusting gain remotely. |
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| Sun
Valley, Calif., November 17, 2000 -- Aphex Systems has been granted a US
Patent for the design of a low-noise, variable-gain amplifier utilized in
the company's ultra-precision Model 1788 Remote Controlled Microphone Pre-amplifier.
The patented circuit is used as a key element in the Model 1788, to provide
input level control from a mixing position, while completely eliminating
the clicks, pops and audio distortion normally associated with remote gain
switching at high gain settings. "In order to maximize signal-to-noise ratio in any signal chain," says Aphex president Marvin Caesar, "it is always preferable to take as much gain as early as possible. That is particularly true in a situation where the low-level signal from the microphone must be boosted to line level, and then processed and amplified or recorded. If there is not sufficient gain in the first stage, gain must be taken in subsequent stages. The noise from the first stage is boosted by the gain of the subsequent stages, and is also combined with the self-noise of the subsequent stages." "Therefore, the best way to maximize noise performance is by riding gain on the mic pre-amplifiers," Caesar continues. "If these pre-amps are located right by the engineer, the gain pots can be easily adjusted. However, when the pre-amps are remote controlled, it is often difficult to smoothly and noiselessly change the gain. Solutions include having an assistant baby-sit the pre-amps - not a very practical option - or use motorized potentiometers - an extraordinarily expensive approach - or use an well-designed electronic circuit." The only viable solution, Aphex designers determined, was an electronic circuit. Because a pre-amp needs to provide 40 dB of variable gain, the circuit has to offer very low self-noise and generate no clicks, pops nor "zipper" effect. Methods exist to minimize these effects, but none to effectively eliminate them. Aphex' new patented circuit topology uses multiplying DACs that, essentially, are resistor arrays. "These resistor arrays are very low noise and distortion," Caesar continues. "If the step sizes are small enough, the amount of noise switching from step to step is minimized, but not eliminated. A phenomenon known as charge injection causes a small click to be generated whenever a switch is made, regardless of the size of the step. With 40 dB of gain, this small click is quite audible." The patented invention, called LeNA, is a method of using pairs of DACs in a differential configuration to cancel out the charge injection. The combination of low step size (the largest is 1/4 dB) and elimination of the charge injection provides the operational benefits of a pre-amp located close to the engineer, with the sonic benefits of a pre-amp close to the microphone. Founded in 1975, Aphex Systems is a leading developer and innovator of signal-processing, dynamics control and analog-to-digital conversion systems designed for a wide cross section of professional end users around the world. For more information call +1/818.767-2929 or visit our internet web site at www.aphex.com. Aphex Systems, Ltd., 11068 Randall Street Sun Valley, CA 91352, USA www.aphex.com Source: Aphex Systems Web: www.aphex.com |
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