High fidelity digital audio sources are capable of reproducing a much wider dynamic rangethan most conventional consumer media (e.g. AM/FM radio and audio cassettes). Theresearch presented here addresses the problem of matching this wide dynamic range tothat of a device ( or channel) with lower dynamic range capabilities using a DynamicRange Controller (DRC). Currently available digital signal processing hardware allowsthe implementation of entirely Digital DRC's (DDRC's) that interface directly to digitalsources and eliminate unnecessary data (analog +--> digital) conversions.The DDRC design presented in this thesis uses an adaptive level measurement schemeand an adaptive recovery time to improve performance. The perceived distortion introducedby rapid gain reductions (attack) is lessened by allowing attacks only at the zerocrossing preceding a transient. A single-channel version of the Adaptive DDRC has beenimplemented for real-time operation on a DSP56000 evaluation board.Tests showed that the Adaptive DDRC has insignificant total harmonic distortion.Intermodulation distortion measurements compare favourably with a previous DDRCdesign [11] that was reported as having good subjective performance. The results of ourlistening tests show great promise for the Adaptive DDRC. Listeners rated the averagesound quality of an Adaptive DDRC configuration higher than a conventional design(with peak level gain control). However, since other Adaptive DDRC configurations (i.e.different parameter sets) did not perform as well, further testing is required to optimizethe Adaptive DDRC parameter set.
展开▼
