Introduction

In this chapter, we present some very useful measures that are necessary to properly design filters in the different domains. These definitions will also help us better understand how noise reduction works in real-world applications and what price we need to pay for this. As a matter of fact, all known approaches in the single-channel (one microphone) case add distortion to the desired signal. Therefore, in most applications, it is essential to find a good compromise between the amount of noise reduction and the degree of speech distortion, and the measures presented in this chapter can guide us to achieve such a compromise.