Abstract
In this paper, we propose a new frequency-dependent amplitude panning method for stereophonic image enhancement applied to a sound source recorded using two closely spaced omni-directional microphones. The ability to detect the direction of such a sound source is limited due to weak spatial information, such as the inter-channel time difference (ICTD) and inter-channel level difference (ICLD). Moreover, when sound sources are recorded in a convolutive or a real room environment, the detection of sources is affected by reverberation effects. Thus, the proposed method first tries to estimate the source direction depending on the frequency using azimuth-frequency analysis. Then, a frequency-dependent amplitude panning technique is proposed to enhance the stereophonic image by modifying the stereophonic law of sines. To demonstrate the effectiveness of the proposed method, we compare its performance with that of a conventional method based on the beamforming technique in terms of directivity pattern, perceived direction, and quality degradation under three different recording conditions (anechoic, convolutive, and real reverberant). The comparison shows that the proposed method gives us better stereophonic images in a stereo loudspeaker reproduction than the conventional method without any annoying effects.
Highlights
Stereo loudspeaker reproduction is widely used to provide a more natural listening experience because of the distinguished relative positions of objects and events in the horizontal plane [1]
In real reverberant recording environments, the DS beamformer changed the direction of stereophonic images due to the reverberant effects [15]. This was because the reverberation time changed according to the frequency, and the DS beamforming weights could not be adapted to this reverberation time change [14]. These results suggest that frequency-dependent amplitude panning for stereophonic image enhancement is necessary for real reverberant environments
We proposed a frequency-dependent stereophonic image enhancement method that could be applied to two closely spaced omni-directional microphones available for portable audio recording devices
Summary
Stereo loudspeaker reproduction is widely used to provide a more natural listening experience because of the distinguished relative positions of objects and events in the horizontal plane [1]. The width or length of the portable device body such as a smart phone or digital camera is approximately 10 cm, the allowable distance between two microphones is less than 3 cm This hardware limitation makes it difficult to match the perceived azimuth angle of the reproduced sound source to the actual that of the original sound source, when a spaced recording technique is applied [8]. We propose frequency-dependent amplitude panning for stereophonic image enhancement when two omni-directional microphones are closely spaced, as deployed in portable devices. In [16,17], frequency-dependent amplitude panning was used to enhance the stereophonic image for portable devices equipped with closely spaced stereo microphones, where the ratio of spectral magnitudes between the left- and right-channel signal was used for the panning.
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