Multi-stream noise predictive filter circuit (502, 504, 506, 508, 510, 512, 514, 516, 700), comprising: - a first noise predictive filter circuit operable to generate a first interim output corresponding to a first data input (Input 1, 122a, 177a) based upon a non-matrix based combination of the first data input (Input 1, 122a, 177a), a previous instance of the first data input (Input 1, 122a, 177a) and a previous instance of a second data input (Input 2, 122b, 177b); - a first square and log function circuit yielding a first processed output based on the first interim output; - a second noise predictive filter circuit operable to generate a second interim output corresponding to the second data input (Input 2, 122b, 177b) based upon a non-matrix based combination of the second data input (Input 2, 122b, 177b), a previous instance of the first data input (Input 1, 122a, 177a) and a previous instance of the second data input (Input 2, 122b, 177b); - a second square and log function circuit yielding a second processed output based on the first interim output; - a combining circuit operable to combine at least the first processed output with the second processed output to yield a combination branch metric (522, 524, 526, 528, 530, 532, 534, 536, 790); - wherein the non-matrix based combination of the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b) is carried out based on - error values between the first data input (Input 1, 122a, 177a), the second data input (Input 2, 122b, 177b) and ideal outputs corresponding to the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b), - variances of the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b) and - respective first and second filter coefficients for the first noise predictive filter circuit and the second noise predictive filter circuit. - a first noise predictive filter circuit operable to generate a first interim output corresponding to a first data input (Input 1, 122a, 177a) based upon a non-matrix based combination of the first data input (Input 1, 122a, 177a), a previous instance of the first data input (Input 1, 122a, 177a) and a previous instance of a second data input (Input 2, 122b, 177b); - a first square and log function circuit yielding a first processed output based on the first interim output; - a second noise predictive filter circuit operable to generate a second interim output corresponding to the second data input (Input 2, 122b, 177b) based upon a non-matrix based combination of the second data input (Input 2, 122b, 177b), a previous instance of the first data input (Input 1, 122a, 177a) and a previous instance of the second data input (Input 2, 122b, 177b); - a second square and log function circuit yielding a second processed output based on the first interim output; - a combining circuit operable to combine at least the first processed output with the second processed output to yield a combination branch metric (522, 524, 526, 528, 530, 532, 534, 536, 790); - wherein the non-matrix based combination of the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b) is carried out based on - error values between the first data input (Input 1, 122a, 177a), the second data input (Input 2, 122b, 177b) and ideal outputs corresponding to the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b), - variances of the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b) and - respective first and second filter coefficients for the first noise predictive filter circuit and the second noise predictive filter circuit. - error values between the first data input (Input 1, 122a, 177a), the second data input (Input 2, 122b, 177b) and ideal outputs corresponding to the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b), - variances of the first data input (Input 1, 122a, 177a) and the second data input (Input 2, 122b, 177b) and - respective first and second filter coefficients for the first noise predictive filter circuit and the second noise predictive filter circuit.