Upmixing and Beamforming in Professional Audio

This chapter presents examples and discusses considerations of different features and quality requirements that are important in professional products. It presents three commercial products that utilize parametric time‐frequency‐domain processing of spatial audio in applications of stereo upmixing, adaptive beamforming, and spatial sound reproduction. In stereo‐to‐multichannel upmixing, a stereophonic signal is rendered to a surround setup with typically five or seven loudspeakers in the horizontal plane around the listener. Time‐frequency upmixing gives a vast improvement in the spatial audio quality when compared to time‐domain matrix upmix. A discrete short‐time Fourier transform (STFT) is used as the time‐frequency representation. The stereo signal is decomposed into direct and ambient sound. Shotgun microphones are an acoustic implementation of a delay‐and‐sum beamformer, based on a single microphone element. The chapter discusses the quality considerations in professional audio that are taken into account in the development of products, such as single‐channel quality and delay.