Note from the Guest Editors

An audibly distinctive test signal, a pink noise signal at a standard level and periodic but brief interruptions (optimized for the ear's memory for level and spectral differences), is applied to a recording medium or transmission channel. The test signal recovered from the recording medium or transmission channel is compared and matched to a reference uninterrupted pink noise signal at a standard level, the interruptions being used to switch between the test and reference signals and to provide an audible cue as to the identity of the signal heard at any moment so that a rapid confirmation and adjustment, if necessary, of recording/reproduction or transmission/reception calibration can be achieved primarily by ear and, if desired, also by applying the signals to measuring instruments.