Patent ID: 8577045

Claim:
An apparatus for encoding a multi channel audio signal, the apparatus comprising: a receiver for receiving the multi channel audio signal comprising at least a first audio signal from a first microphone and a second audio signal from a second microphone; a time difference unit for determining an inter time difference between the first audio signal and the second audio signal by combining successive observations of cross-correlations between the first audio signal and the second audio signal for a plurality of offsets for determining the inter time difference in response to the cross correlations and where the cross-correlations are processed to derive probabilities that are accumulated using a modified Viterbi algorithm and wherein the time difference unit comprises a trellis state machine having a plurality of states, each of the plurality of states corresponding to a time offset of the plurality of time offsets; a path unit for determining path metrics for states of the trellis state machine in response to the cross correlations; a probability unit for determining state probability metrics for the states in response to path metrics associated with paths from previous states to current states; a unit for determining the inter time difference in response to the state probability metrics; and a unit for dividing the first audio signal and the second audio signal into a plurality of frames; and the time difference unit is arranged to, for each state of the states of the trellis state machine, determining a new state probability metric in response to a previous state probability metric for the state and correlation coefficients for a subset of time offsets; a delay unit for generating a compensated multi channel audio signal from the multi channel audio signal by delaying at least one of the first audio signal and the second audio signal in response to the inter time difference signal; a mono unit for generating a mono signal by combining channels of the compensated multi channel audio signal; and a mono signal encoder for encoding the mono signal.