Chapter Excerpts

Chapter 14: Signal Processing

One could reasonably argue that anything interposed between the original source of sound and the listener constitutes signal processing. Many recording and sound reinforcement engineers, for example, select microphones based upon how the microphone alters the quality of the sound in the final product.

Some microphones provide a boost in the 2 kHz to 4 kHz region and are said to add “presence.” Cardioid microphones when worked at a close distance exhibit a “proximity effect” that amounts to a bass boost that can add body to a weak or thin voice. For the present purpose, however, signal processing, will be confined to certain properties of the signal chain that exists between the microphone or microphones and the loudspeaker or loudspeakers. Much of this processing is linear and time invariant in that it does not depend on the signal amplitude or the time of occurrence of the signal in question. In some instances the processing is non-linear such as noise gates, downward expanders, and compressors as well as limiters. Amplifiers also exist in this signal chain. Wide bandwidth linear amplifiers other than offering voltage and or power amplification are essentially benign and as such and are not considered as signal processors per se.