Acoustic feedback correction

A filter apparatus for correcting feedback from a loudspeaker to a microphone, said apparatus comprising:

• an adaptive digital filter which, in use, receives an incoming signal and provides a modelled feedback signal for subtraction from an outgoing signal to provide a corrected outgoing signal;
• and
• means for changing the weights of said filter in accordance with an algorithm for reducing the difference between an actual feedback signal and said modelled feedback signal, each weight change including a variable scaling factor which varies in accordance with the ratio of a first value indicative of the long-term average power of the sound being fed back to a second value indicative of the short-term average power of the sound being fed back;
• wherein said first and second values are derived from said outgoing signal;
• and
• if said second value is less than a threshold value then said second value is set to the threshold value.

A filter apparatus for correcting feedback from a loudspeaker to a microphone, said apparatus comprising:

• an adaptive digital filter which, in use, receives an incoming signal and provides a modelled feedback signal for subtraction from an outgoing signal to provide a corrected outgoing signal;
• and
• means for changing the weights of said filter in accordance with an algorithm for reducing the difference between an actual feedback signal and said modelled feedback signal, each weight change including a variable scaling factor which varies in accordance with the ratio of a first value indicative of the long-term average power of the sound being fed back to a second value indicative of the short-term average power of the sound being fed back;
• wherein said first and second values are derived from said outgoing signal;
• and
• if power of said incoming signal is less than an incoming signal power threshold value when said second value is set to a predetermined value.

A filter apparatus for correcting feedback from a loudspeaker to a microphone, said apparatus comprising:

• an adaptive digital filter which, in use, receives an incoming signal and provides a modelled feedback signal for subtraction from an outgoing signal to provide a corrected outgoing signal;
• and
• means for changing the weights of said filter in accordance with an algorithm for reducing the difference between an actual feedback signal and said modelled feedback signal, each weight change including a variable scaling factor which varies in accordance with the ratio of a first value indicative of the long-term average power of the sound being fed back to a second value indicative of the short-term average power of the sound being fed back;
• wherein a first partial weight change which is not dependent on said variable scaling factor, and a second partial weight change which is dependent on said variable scaling factor are added in predetermined proportions to provide said weight change.

An echo cancelling apparatus comprising a filter apparatus for correcting feedback from a loudspeaker to a microphone, said filter apparatus comprising:

• an adaptive digital filter which, in use, receives an incoming signal and provides a modelled feedback signal for subtraction from an outgoing signal to provide a corrected outgoing signal;
• and
• means for changing the weights of said filter in accordance with an algorithm for reducing the difference between an actual feedback signal and said modelled feedback signal, each weight change including a variable scaling factor which varies in direct accordance with the ratio of a first value indicative of the long-term average power of the sound being fed back to a second value indicative of the short-term average power of the sound being fed back;
• wherein said adaptive filter provides a first modelled feedback signal for subtraction from the outgoing signal to provide a first corrected outgoing signal;
• the echo cancelling apparatus further comprising:
• a static filter which, in use, receives the incoming signal and provides a second modelled feedback signal for subtraction from the outgoing signal to provide a second corrected outgoing signal;
• a comparator means for comparing said first and second corrected outgoing signals and outputting the lower of the two signals as a corrected outgoing signal;
• and
• means for substituting the weights of said adaptive filter into the static filter on said first corrected outgoing signal being lower than said second corrected outgoing signal.

A filter apparatus for correcting acoustic feedback from a loudspeaker to a microphone, said apparatus comprising:

• means for splitting an incoming signal into a plurality of frequency-banded incoming signals;
• means for splitting the outgoing signal into a plurality of frequency-banded outgoing signals;
• a plurality of adaptive filters, operable to receive respective ones of said frequency-banded incoming signals, and to provide respective modelled frequency-banded feedback signals for subtraction from respective frequency-banded outgoing signals to provide respective frequency-banded corrected outgoing signals;
• means for changing the weights of the filters in accordance with an algorithm for reducing the difference between the frequency-banded outgoing signals and respective modelled frequency-banded feedback signals, the weight changes including variable scaling factors which vary in direct accordance with the respective ratios of a first value indicative of the long-term average power within a frequency-band of the sound being fed back to a second value indicative of the short-term average power within the frequency-band of the sound being fed back;
• and
• means for combining said plurality of frequency-banded corrected outgoing signals to provide a corrected outgoing signal.