Time–Frequency Processing: Methods and Tools

This chapter presents an overview of the theory and practice of the tools typically needed in time-frequency processing of audio channels. It introduces a few signal processing techniques commonly used, and serves as background information for the reader. The chapter assumes understanding of basic digital signal processing techniques from the reader, which can be obtained from such basic resources as Oppenheim and Schafer or Mitra and Kaiser. It discusses the methods that utilize some kind of stochastic analysis of time-frequency domain differences between microphone signals. In the reproduction of spatial audio, the computed time-frequency-dependent parameters are typically used to control the mixing process, where in some cases decorrelation of signals is used to control the coherence between output channels. The chapter describes an optimal method to control the level of decorrelated signal energy that is utilized in some of the spatial audio methods.