DC Servos and Digitally-Controlled Microphone Preamplifiers
by Gary Hebert, CTO THAT Corporation
Microphone preamplifiers for professional audio applications require a very wide range of gain and low noise in order to provide a high-quality interface with the vast number of available microphones. In many modern systems the preamplifier gain is controlled indirectly via a digital interface in discrete steps. Often dc servo amplifiers are employed as a means of keeping the dc gain fixed to avoid large changes in output offset voltage while the audio band gain is varied. The resulting highpass filter response varies substantially as a function of the preamplifier gain. We investigate the frequency and time-domain effects of this. We also investigate several approaches to minimize these effects. Convention Paper 9198.
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About THAT Corporation
THAT Corporation, founded in 1989, designs and sells high-performance analog integrated circuits for professional audio manufacturers. THAT’s ICs include analog input and output stages, digitally controlled low-noise preamplifiers, Analog Engines® and its original line of voltage-controlled amplifiers (VCAs) – all used throughout the pro audio industry. The company also licenses patents, trademarks, and other intellectual property to the TV broadcast and reception industries. Licensed products include the dbx-tv® Total™ series of audio enhancement technology and digital implementations of legacy TV audio receiver standards. The company is headquartered in Milford, Massachusetts, with offices in Milpitas, California.
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