Processing of microphone signals for spatial playback
Disclosed are methods and systems which convert a multi-microphone input signal to a multichannel output signal making use of a time-and frequency-varying matrix. For each time and frequency tile, the matrix is derived as a function of a dominant direction of arrival and a steering strength parameter. Likewise, the dominant direction and steering strength parameter are derived from characteristics of the multi-microphone signals, where those characteristics include values representative of the inter-channel amplitude and group-delay differences.
1 . A method of processing audio, comprising:
receiving an input signal including a plurality of microphone signals;
determining a mixing matrix based on characteristics of the input signal; and
mixing the input signal according to the mixing matrix to produce a multichannel audio output signal including a plurality of output channels, wherein determining the mixing matrix comprises:
calculating a covariance matrix based on a frequency representation of the input signal, wherein the covariance matrix is smoothed over a predetermined time window;
based on the covariance matrix:
determining a vector representative of a dominant direction of arrival and a parameter representative of a degree to which the input signal appears to contain a dominant direction of arrival; and
determining the mixing matrix based on a weighted sum of a first matrix that is independent of the dominant direction of arrival and based on a second matrix that correlates to the dominant direction of arrival, wherein the first matrix is weighted by a first weight that decreases for an increase in value of the parameter, and wherein the second matrix is weighted by a second weight that increases for an increase in value of the parameter.
2 . A system comprising:
one or more processors; and
a non-transitory computer readable medium storing instructions that, when executed by the one or more processors, cause the one or more processors to perform operations of processing audio, the operations comprising:
receiving an input signal including a plurality of microphone signals;
determining a mixing matrix based on characteristics of the input signal; and
mixing the input signal according to the mixing matrix to produce a multichannel audio output signal including a plurality of output channels, wherein determining the mixing matrix comprises:
calculating a covariance matrix based on a frequency representation of the input signal, wherein the covariance matrix is smoothed over a predetermined time window;
based on the covariance matrix:
determining a vector representative of a dominant direction of arrival and a parameter representative of a degree to which the input signal appears to contain a dominant direction of arrival; and
determining the mixing matrix based on a weighted sum of a first matrix that is independent of the dominant direction of arrival and based on a second matrix that correlates to the dominant direction of arrival, wherein the first matrix is weighted by a first weight that decreases for an increase in value of the parameter, and wherein the second matrix is weighted by a second weight that increases for an increase in value of the parameter.