Improved Time Delay Analysis/Synthesis for Parametric Stereo Audio Coding

For parametric stereo and multi-channel audio coding, it has been proposed to use level difference, time difference, and coherence cues between audio channels to represent the perceptual spatial features of stereo and multi-channel audio signals. In practice, it has turned out that by merely considering level difference and coherence cues a high audio quality can already be achieved. Time difference cue analysis/synthesis did not contribute much to a higher audio quality, or, even decreases audio quality when not done properly. However, for binaural audio signals, e.g. binaural recordings or signals mixed with HRTFs, time differences play an important role. We investigate problems of time difference analysis/synthesis with such critical signals and propose algorithms for improving it. A subjective evalution indicates significant improvements over previous time difference analysis/synthesis

Design and Limitations of Non-Coincidence Correction Filters for Soundfield Microphones

The tetrahedral microphone capsule arrangement in a Soundfield microphone captures a so-called A-format signal which is then converted to a corresponding B-format signal. The phase differences between the A-format signal channels due to non-coincidence of the microphone capsules cause errors in the corresponding B-format signals and linear combinations thereof. Various strategies for designing B-format non-coincidence correction filters are compared and limitations are discussed.LCA

Binaural reverberation using a modified Jot reverberator with frequency- dependent interaural coherence matching

An extension of the Jot reverberator is presented, producing binaural late reverberation where the interaural coherence can be controlled as a function of frequency such that it matches the frequency-dependent interaural coherence of a reference binaural room impulse response (BRIR). The control of the interaural coherence is implemented using linear filters outside the reverberator’s recursive loop. In the absence of a reference BRIR, these filters can be calculated from an HRTF set

Stereo Acoustic Echo Control Using A Simplified Echo Path Model

In handsfree tele- or video-communication, acoustic echoes arise due to the coupling between the loudspeakers and microphones. It is much more challenging to remove the undesired acoustic echoes for stereo or multi-channel tele-communication systems than for mono systems due to the non-uniqueness problem. While non-uniqueness can be prevented by introducing independent distortions into the left and right loudspeaker signals, stereo echo cancellation is more challenging in terms of convergence speed and computational complexity than mono echo cancellation. The proposed stereo echo control algorithm circumvents the non-uniqueness problem by using simplified echo path models consisting of delays and short-time spectral modification. It is shown that for reasonably symmetric systems the left and right echo path models are similar enough that a single echo path model can be used for estimating the total echo power spectrum and a gain filter for removing the echo from the microphone channels. The proposed algorithm is also applicable to multi-channel systems and the computational complexity is very low