Conversion of nearly monaural audio to 5.1-channel audio for portable multimedia devices

In this paper, an upmixing method is proposed which converts nearly monaural audio signals into 5.1-channel ones for portable multimedia devices. Since spatial information is not clear due to close spacing between stereo microphones in portable devices, the proposed method tries to estimate the source direction depending on the frequency using azimuth-frequency analysis instead of directly estimating the inter-channel time difference or the inter-channel level difference between the two microphones. Then, a frequency-dependent amplitude panning technique is proposed to generate 5.1-channel audio signals. The performance of the proposed method is evaluated by examining the directivity patterns of upmixed 5.1-channel audio signals. Consequently, it is shown that the proposed method provides better directivity patterns than a conventional method based on passive surround decoding.