Objective evaluation of diffuseness in multichannel audio reproduction

The reproduction of diffuse sound is one of the important issues in multichannel audio. In the room acoustics, the interaural cross-correlation coefficient (IACC) is known as an objective measure of diffuseness. It uses a binaural signal recorded by a dummy-head microphone set in the sound field. In the audio reproduction, however, the IACC is not a good measure because the diffuse sound comes only from the loudspeakers’ directions instead of every direction. Although the inter-channel cross-correlation coefficient (ICC) among channel signals has been used to estimate the diffuseness of audio reproduction, the actual diffuseness in the reproduction should be dependent on loudspeaker positions of the reproduction system. This study addresses a new method for objective evaluation of diffuseness in audio reproduction based on the binaural signal. The method analyzes the influence of loudspeakers on the interaural cross-correlation function (IACF) and uses a weighting function for IACF to reduce the influence. The weighted IACC that is obtained from the weighted IACF is then proposed as a new measure of diffuseness for audio reproduction. Subjective evaluation experiment was conducted using binaural sound materials recorded by a dummy-head microphone set in the sound field of audio reproduction. Eleven people evaluated these binaural signals by a headphone reproduction paying attention to the diffuseness and timbre of sound. The subjective evaluation results were compared with the calculated values by the new method. As the result, it is found that the values accorded with the subjective evaluation results, meaning that the new method can generate an appropriate objective measure of diffuseness for audio reproduction.