Beamformed microphone array
According to a first aspect of the invention, there is provided a method of beamforming for a linear microphone array comprising: storing a desired end-fire beam response including a beamwidth specification; determining an error data set from the stored end-fire beam response; and determining beamforming weights based on a least squares minimisation of the error data set. There are also provided a system, a microphone array, and an apparatus.
1 . A method of beamforming for a plurality of linear microphone arrays within a three-dimensional housing, comprising:
storing a desired end-fire beam response including a beamwidth specification;
determining and storing diffraction behaviors around a microphone array of the plurality of linear microphone arrays;
compensating for the diffraction behaviors by including a diffraction compensation factor;
determining an error data set from the stored end-fire beam response and the diffraction compensation factor; and
determining beamforming weights based on a least squares minimization of the error data set.
2 . The method of claim 1 , further comprising weighting the error data set.
3 . The method of claim 1 , further comprising regularizing the least squares minimization of the error data set.
4 . The method of claim 1 , further comprising an inverse Fourier transformation and a convolution operation.
5 . The method of claim 1 , wherein the beamforming weights low-pass filter the response of a first microphone of the microphone array with a first cut-off frequency and low-pass filter the response of a second microphone of the microphone array with a second cut-off frequency different from the first cut-off frequency, wherein the microphone array has a center, the first microphone is closer to the center than the second microphone, and the first cut-off frequency is higher than the second cut-off frequency.
6 . The method of claim 1 , wherein the beamwidth of an end-fire beam beamformed using the determined beamforming weights varies by no more than 50% across the frequency range of 2000 Hz to 16000 Hz.
7 . The method of claim 1 , wherein the stored desired end-fire beam response is part of a noise-filtering algorithm and is a first main beam, further comprising storing a second beam response including a beamwidth specification different from the beamwidth specification of the stored desired end-fire beam response, wherein the second beam response is also part of the noise-filtering algorithm and is also an end-fire main beam.
8 . The method of claim 1 , wherein the stored desired end-fire beam response is part of a noise-filtering algorithm and is a first null beam, further comprising storing a second beam response including a beamwidth specification different from the beamwidth specification of the stored desired end-fire beam response, wherein the second beam response is also part of the noise-filtering algorithm and is also a null beam.
9 . The method of claim 1 , further comprising compensating for diffraction behaviors of the physical microphone array structure.
10 . A non-transitory computer readable medium having stored thereon software instructions that, when executed by a processing unit, cause the processing unit to perform the method of claim 1 .
11 . A system, comprising:
a processing unit; and
a microphone array comprising a plurality of linear microphone arrays within a three-dimensional housing;
wherein the processing unit is configured to receive audio from the plurality of linear microphone arrays and apply the method of beamforming of claim 1 to the received audio to generate an end-fire beam.
12 . The system of claim 11 , wherein the processing unit is in the same physical package as the microphone array.
13 . The system of claim 11 , wherein the processing unit is a ground station.
14 . The system of claim 11 , wherein the processing unit is configured to sum outputs of one or more microphones of the plurality of linear microphone arrays.
15 . The system of claim 11 , wherein the processing unit is configured to beamform multiple beams, and wherein a second beam of the multiple beams is wider than the end-fire beam.
16 . The system of claim 15 , wherein the end-fire beam is more sensitive than the second beam to the position of a target audio source, and the second beam is more sensitive than the end-fire beam to the position of a noise source.
17 . The system of claim 16 , wherein the processing unit is further configured to execute a noise-filtering algorithm that uses the second beam to reduce the power of any noise signal of the noise source captured by the end-fire beam, and wherein the end-fire beam is an end-fire main beam.
18 . The system of claim 11 , further comprising
a plurality of filters, each filter is configured to receive a respective output signal from a respective linear microphone array of the plurality of linear microphone arrays, each filter is configured to have at least one associated coefficient or constant, and wherein a plurality of filtered signals output from each of the plurality of filters are configured to be combined into a smaller subset of beamformer outputs; and
a user beamformer selection input configured to receive a user selection, and depending on the selection to adjust the coefficient or constant associated with each filter to achieve a desired smaller subset of beamformer outputs and/or resulting beamforming pattern.
19 . The system of claim 18 , further comprising
a control housing;
a data connection between the microphone housing and the control housing;
a processor within the control housing or the microphone housing configured to form an end-fire beam response from the outputs of the plurality of linear microphone arrays; and
one or more user input devices on the control housing configured to adjust the end-fire beam.
20 . The system of claim 19 , further comprising
an output providing an end-fire beam response from the smaller subset of beamformer outputs, wherein the sidelobe response of the output is considerably lower than an interference tube shotgun mic.