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Jul 23 2024


7:00 pm - 9:30 pm

AES United Kingdom Section Event – Analogue Voltage Controlled Amplifiers/Attenuators (VCAs): A Gentle Introduction

How on earth did we electronically vary the amplitude of an audio signal before Digital Signal Processing (DSP)?  In the digital domain varying the amplitude of an audio signal is simple. You simply multiply the sample value by a coefficient. For example, “0.5” , “0.01”, “0. 007”, etc… and the job is done. There are some issues with “zipper noise”, but basically, that’s it! However analogue is a different story, because we need to change a value in an analogue circuit. Often, the circuit  needed to do this is non-linear and many creative approaches have been invented to do this. They are generally called “Voltage Controlled Amplifiers/Attenuators” or VCAs for short.

The purpose of this talk is to introduce you to the many weird and wonderful ways this was done in the past. Our speaker Professor Jamie Angus-Whiteoak will start with a quick look at the VCA family tree and then go through the different main approaches. Explaining how each method works and discussing their limitations and problems, as well as some solutions to those problems. We will also discuss how these limitations interacted with the design of circuits that used them and show examples of each one in use.  Intriguingly this will cover some classic bits of audio processing “gear”!

The presentation will be accessible and will not require any deep knowledge of either devices or circuits, but should give you a good overview of how analogue VCAs work and give such legendary results.

Speaker Bio:

Jamie Angus-Whiteoak is Emeritus Professor of Audio Technology at Salford University. Her interest in audio was crystallised at age 11 when she visited the WOR studios in NYC on a school trip in 1967. After this she was hooked, and spent much of her free time studying audio, radio, synthesisers, and loudspeakers, and even managed to build some! She has worked in both industry and academia in diverse fields from integrated optics and acoustics to analogue and digital signal processing. Her expertise ranges from valve (tube) circuits to the applications of esoteric number theory in signal processing. She has pioneered degree level courses in both music technology and electronic engineering in the UK. She is the inventor of modulated, wideband, and absorbing diffusers, direct processing of Super Audio CD signals, and one of the first 4-channel digital tape recorders. She has done work on signal processing, analogue circuits, diffusers, and numerous other audio technology topics.

Jamie has been active in the AES for 33 years, is a member of the Diversity, Equity and Inclusion, and Education Committees, and is currently VP for the Northern Europe Region. She has also been Papers Co-Chair for several conventions, as well as a judge for the Saul Walker Student Design and MATLAB Student Plugin competitions. Jamie has been awarded an AES fellowship, the Institute of Acoustics Peter Barnet Memorial Award, the AES Silver Medal Award, and the AES Gold Medal Award, for extraordinary contributions as an innovator and inventor in the fields of audio science, acoustics, and signal processing. For relaxation she likes playing drums and dancing, but not at the same time.

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