Fast Generation of Sound Zones Using Variable Span Trade-Off Filters in the DFT-Domain

The creation of sound zones with frequency-domain variable span trade-off filters (VAST) is investigated herein. Both narrowband and broadband discrete Fourier transform (DFT)-domain VAST approaches are proposed, and we discuss their relationship to the existing time-domain VAST approach. The core idea in VAST is to apply a generalized eigenvalue decomposition to the spatial statistics to control the trade-off between acoustic contrast and signal distortion. Moreover, a method for determining the optimal Lagrange multiplier that controls this trade-off is also considered in terms of physical, meaningful parameters. Through analysis and experiments, a performance comparison using measured room impulse responses is conducted not only between the two proposed methods but also between the two proposed methods and the existing time-domain approach. The results confirm that the broadband approach is able to transfer the acoustic contrast from one frequency bin to another, which is not the case for the narrowband approach. Furthermore, the results also show that the proposed DFT-domain VAST approach can be considered to be a special case of the time-domain VAST approach.