Abstract:
Audio processor for processing a set of input audio channels and generate a corresponding processed set of signals adapted for playback via a set of narrow-spaced loudspeakers with the purpose of providing a spatial image widening effect. The audio processor includes a cross talk canceller active only in a pre-selected frequency range, e.g. 1.5-18 kHz, and substantially in-active outside this frequency range. In addition, the audio processor includes applying substantially similar frequency weightings to the two input audio channels within the mentioned pre-selected frequency range. This frequency weighting is selected such that the processed set of signals provides a listener with a perceived timbre being substantially the same as a perceived timbre provided by the input set of audio signals. The frequency weighting is preferably based on a magnitude of an ipsi-lateral or a contra-lateral transfer function, or based on a square root of sum of squares of magnitudes of ipsi-lateral and contral-lateral transfer functions. The audio processor is advantageous since it provides a high sound quality without severe tonal coloration and with a stable spatial widening effect tolerant to listener head movements in spite of very narrow-spaced loudspeakers, such as with a listening angle of 4° or less, e.g. in a mobile phone or other handheld devices. In addition, the processor is advantageous in that it provides a high reproduction quality of both timbre and spatial aspects for normal stereo signals as well as binaural signals, including 3D spatial content in case of binaural input signals, without the need to adapt the processing to the actual input signal type.
Abstract:
A method and a system for equalizing one or more loudspeaker(s), e.g. a hi-fi system, positioned in a room in order to compensate sound reproduction from the loudspeaker for an influence of the room. The method includes measuring a listening position transfer function (L) from electrical input of the loudspeaker (L1) to a sound pressure at a listening position (LP) in the room. A global transfer function (G) representing a spatial average of sound pressure level in the room generated by the loudspeaker (L1) is determined. This global transfer function (G) can either be determined as an average of two or more transfer functions measured in field points scattered across the room or it can be calculated based on an acoustic power output measured from the loudspeaker (L1) together with data regarding sound absorption properties of the room. An upper gain limit (UGL) as a function of frequency is then determined based on an inverse of the global transfer function (G). An equalizing filter (F) is then determined based on an inverse of the listening position transfer function (L), but with its gain being limited to a maximum gain in accordance with the upper gain limit (UGL). Finally, the loudspeaker (L1) is equalized with the equalizing filter (F), the filter (F) being implemented such as a minimum phase approximation by an FIR or an HR filter. Preferably, a lower gain limit (LGL) as a function of frequency is also determined as an inverse of the global transfer function (G), wherein a gain of the equalizing filter (F) is limited to a minimum gain in accordance with the lower gain limit (LGL). By use of the upper and lower gain limits (UGL, LGL) it is possible to implement a system capable of automatically designing the equalizing filter (F) with only simple tasks to perform for an operator of the system.