In accordance with a first aspect of the present invention there is
provided a telephone apparatus including a transmitter portion and a
receiver portion, an input transducer for converting input audio signals
into electrical signals, a connectable input link between the input
transducer and the transmitter portion to deliver when connected an input
electrical signal to the transmitter portion to be transmitted by the
transmitter portion, an output transducer for converting an output
electrical signal into an audio signal and a connectable output link
between the receiver portion and the output transducer for delivering
when connected an output signal to the output transducer, optionally an
echo cancellation circuitry portion adapted to sample the output signal
and produce an echo replica signal, optionally a mixer included in the
input link for mixing an echo replica signal produced by the echo
cancellation circuit with an input signal produced by the input
transducer, and an echo suppression circuitry portion including detector
means for producing a first magnitude signal which represents a magnitude
property of a first sample of an output signal S.sub.o in the output link
and a second magnitude signal which represents a magnitude property of a
second sample of an input electrical signal S.sub.i in the input link
between the mixer and the transmitter portion, an analyzer, connected to
receive inputs comprising the first and second magnitude signals from the
detector means, for measuring a relationship between the first and second
magnitude signals and for producing a control signal when the
relationship exceeds a threshold, wherein the detector means is operable
periodically to analyse characteristics of the signal S.sub.o to estimate
the amount of background noise in the signal S.sub.o and to pass as an
input to the analyzer a signal representing the estimated amount of
backgroudn noise wherein the threshold above which the analyzer produces
an output control signal is set adaptively by the analyzer dependent on
the estimated background noise.
