The proper interconnection of analog audio signals, and an understanding of the principles of balanced and unbalanced lines, is vital to the maintenance of high quality in an audio system, and will remain important for many years notwithstanding the common usage of digital systems. Unbalanced lines are normally terminated in connectors such as phono plugs, DIN plugs, and quarter-inch 'A-gauge' jack plugs. The balanced line is better at rejecting interference than the unbalanced line, and improvements upon the performance of the unbalanced line in this respect can be 80 dB or more for high-quality microphone lines. Balanced lines are used for professional audio connections because of their greatly superior rejection of interference, and this is particularly useful when sending just a few precious millivolts from a microphone down many meters of cable to an amplifier.