The desired signal of the standard MWF (S-MWF) is usually the speech component in one of the microphone signals, referred to as the reference microphone signal.
The reference microphone signal is used to derive an adaptive threshold by opening the gate only if the input signal magnitude is grater than the reference microphone magnitude signal.
where X l (k,n) denotes the lth plane wave as received by a reference microphone, a l (k,n) is the relative propagation vector of the lth plane wave from the reference microphone to all M microphones, d k,n) is the diffuse sound, and v k,n) is the additive noise.
For each hearing aid, we consider one of the microphones to be the reference microphone, i.e., disregarding equalization effects the receiver signal would optimally be equal to the reference microphone signal in the absence of noise.
The first input is the reference microphone, which picks up the unwanted noise.
Hence, the reference microphone selection determines the amount of speech distortion.
For spatially distributed microphones, the selection of the reference microphone may have a large influence on the performance of the MWF depending on the positions of the speech/noise sources and the microphones [5 7, 17].
The transfer function represents the primary path from the reference microphone to the error microphone, and is the secondary-path transfer function between the output of adaptive filter and the output of error microphone.
Though the algorithm was good, the reference microphone was an unpredictable variable: it had practical placement problems.
