ABSTRACT
There are several standards for line signal levels. In any audio system it is necessary to select a suitable nominal level for the signal passing through it. If the incoming signal does have to be amplified, this should be done as early as possible in the signal path, to get the signal well above the noise floor. RF filtering is applied at the very front end to prevent noise breakthrough and other EMC problems. It must be done before the incoming signal encounters any semiconductors where RF demodulation could occur, and can be regarded as a ‘roofing filter’. Balanced inputs are used to prevent noise and crosstalk from affecting the input signal, especially in applications where long interconnections are used. They are standard on professional audio equipment, and are slowly but steadily becoming more common in the world of hifi. An interfering signal at significant voltage couples directly to the inner signal line, through stray capacitance.
