Apparatus And A Method For Audio Signal Processing

Abstract

An apparatus, such as a headset, configured to process audio signals from multiple microphones, comprising: a first pair of microphones (101, 102) outputting a first pair of microphone signals and a second pair of microphones (103, 104) outputting a second pair of microphone signals; a first beamformer (105) and a second beamformer (106) each configured to receive a pair of microphone signals and adapt the spatial sensitivity of a respective pair of microphones as measured in a respective beamformed signal (XL; XR) output from a respective beamformer (105; 106); wherein the spatial sensitivity is adapted to suppress noise relative to a desired signal; a third beamformer (107) configured to dynamically combine the signals (XL; XR) output from the first beamformer (105) and the second beamformer (106) into a combined signal (XC); wherein the signals are combined such that signal energy in the combined signal is minimized while a desired signal is preserved; and a noise reduction unit (109) configured to process the combined signal (XC) from the third beamformer (107) and output the combined signal such that noise is reduced.

Description

[0001]It has been discovered that use of multiple microphones and the use of beamforming techniques provide audio signal reproduction that is superior to single microphone or non-beamforming systems. The multiple microphones are located at different positions and allows so-called spatial sampling which in turn enables cancelling of noise interfering with a desired signal such as a person's voice; this is also known as beamforming, spatial filtering or noise-cancelling. Subsequent time varying post-filters are often applied as a means to further discriminate the person's voice from (background) noise signals.[0002]Multiple microphones and the use of beamforming techniques are frequently embodied in headsets, hearing aids, laptop computers and other electronic consumer devices.[0003]The technical field of beamformers has been extensively researched; however their qualities and configurations have not been fully exploited.RELATED PRIOR ART[0004]US 2012 / 0020485 discloses an audio signal...

AI Technical Summary

Benefits of technology

[0011]By arranging the microphones, such that intra-pair microphones sit closer than inter-pair microphones at least when the apparatus is in normal operation and intra-pairs in end-fire configurations, the first and the second beamformer can take advantage of any near-field effect to cancel or suppress more noise at low frequencies and in addition make it possible to cancel more noise at higher frequencies, avoiding spatial aliasing. Additionally, the third beamformer can take advantage of the different local noise levels that the different pairs of microphones are exposed to. When the microphone pairs sit on different sides of a person's head, the head may form a wind and / or sound shadow reducing noise level on one side of the person's head. It is a major advantage of the invention that the highly complex problem of designing a single adaptive beamformer operating on all microphone inputs is decomposed into three simple, robust, well-understood dual-microphone beamformers.

[0012]In general, different types of microphones with different characteristics may be selected.

[0013]A desired signal is a signal that typically represents voice from a speaker within proximity of the microphones or voice appearing from a certain direction relative to the orientation of the microphones. A desired signal may be characterised by being emitted from one or more sound sources having predefined spatial locations with respect to the spatial location of the microphones. Since multiple microphones are used to pick up the desired signal the desired signal may be characterised by a predefined phase and / or amplitude difference among the microphone signal and / or among beamformed signals. A desired signal may also be characterised by a predefined temporal characteristic and / or a predefined phase- / amplitude-frequency characteristic.

[0014]A noise signal or simply noise may include turbulence sounds induced by wind occurring at sufficiently high wind speeds and acting on the microphone membranes. Noise may also include background sounds such as tones from machines, sounds from items rattling or chinking, sounds from people talking amongst each other, etc. In some definitions, noise is characterised by being emitted from one or more sound sources that are located at other locations than the desired signal.

[0015]The first beamformer and the second beamformer adapt the directional sensitivity gradually or in steps e.g. comprising sensitivities that are at least approximated from the group of the following characteristics: Omni-directional, bi-directional, cardioid, subcardioid, hypercardioid, supercardioid or shotgun. The directional sensitivity may be changed gradually between an omni-directional, a bi-directional and a cardioid characteristic. The first beamformer may be configured as disclosed in WO 2009 / 132646 which is hereby incorporated by reference for everything disclosed in connection with especially FIG. 1 thereof.

[0016]The third beamformer may combine the signals from the first and the second beamformer in accordance with coefficients estimated from noise powers. In case the noise power of the signal from the first beamformer is higher than the noise power of the signal from the second beamformer, the signal from the second beamformer is weighted higher than the signal from the first beamformer and vice versa. The noise level of a signal may be estimated when voice is detected as not present.

Problems solved by technology

Furthermore, the first and the second beamformers may not be able to cancel the noise equally well, depending on the relative position of the microphone pair, the signal of interest and interfering noises.

As a consequence, the noise may not be suppressed equally well and / or the desired signal may not be preserved equally well.

When noise reduction is performed, there is a risk of introducing voice processing artifacts that degrades voice quality.

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