On reduction of positive feedback by audio frequency processing techniques

Abstract

Reduction of positive feedback between a loudspeaker and a microphone through shifting the frequency of the signal received by the microphone from that of the output signal from the loudspeaker can increase the stability of the system. The amplifier output can be increased by an amount of 6dB without affecting the stability. Therefore in this thesis we will study a technique of shifting frequency of the signal. The input signal sin 2 π ft and the shifted frequency signal sin 2 π∆ft which is generated by a signal generator are processed to yield the quadrature signals cos 2 π ft, and cos 2 π ∆ ft, All signals are then multiplied and added together to form (sin 2 π ft cos 2 π ∆ ft + cos 2 π ft sin 2 π ∆ ft) which is equal to sin 2 π (f + ∆ f) t. This shows that the (∆ f) frequency shift is achieved. In the study the signals sin 2 π ft, cos 2 π ft, sin 2 π ∆ ft, cos 2 π ∆ ft are generated and processed to give the desired function, then the accomplished result is tested for the additional stable gain of the system.