Browse Prior Art Database

AUDIO LEVEL CONTROL USING DUTY-CYCLE MODULATION

IP.com Disclosure Number: IPCOM000005449D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 76K

Publishing Venue

Motorola

Related People

Darrell E. Davis: AUTHOR

Abstract

Described herein is a novel method for audio volume control for use on non-linear mechanically reso- nant audio transducers. This method provides volume control without complex linear circuitry. This method is easily implemented digitally, as part of a systems program or in special purpose hardware.

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Technical Developments Volume 2

January 1982

AUDIO LEVEL CONTROL USING DUTY-CYCLE MODULATION

By Darrell E. Oavis

   Described herein is a novel method for audio volume control for use on non-linear mechanically reso- nant audio transducers. This method provides volume control without complex linear circuitry. This method is easily implemented digitally, as part of a systems program or in special purpose hardware.

   In the trend toward electronic volume controls as a replacement for mechanical volume controls, a need exists for a simple method to change the audio volume of a simple single frequency tone. Present and past electronic means use transconductance amplifiers or switched resistor ladders. These prove somewhat complex, expensive and not compatible with large scale system integration.

   Since the driven transducer is run at (or very near) its particular mechanical resonance, the transducer possesses the characterlstlcs of a bandpass filter. In this event, it efficiently converts &SC- trical energy to acoustical energy at the resonant frequency. This phenomena allows the transducer to be driven by a wide variety of electrical waveforms and produce identical audio levels (providing the power at the fundamental frequency of these waveforms is equal). Since the fundamental frequency content of a duty cycle modulated square wave is proportional to the duty cycle, the power in the fundamental fre- quency can be varied by changing the duty cycle. This becomes the basis...