1. 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, 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 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 i in the input link, an analyser, 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 o to estimate the amount of background noise in the signal S o and to pass as an input to the analyser a signal representing the estimated amount of background noise wherein the threshold above which the analyser produces an output control signal is set adaptively by the analyser dependent on the estimated background noise.