Reverberation, artificial  --  Can be used to make vocalists sound better, but also applied in varying degrees to instrumental sounds. Short single delays added to the original give overdubbing effects, sounding like two voices or instruments in unison. Several short delays can make two or three voices sound like a chorus. Longer delays give echoes. Echo plates and spiral steel springs having transducers to impart and pick up sound vibrations have been the standard means of obtaining these effects. Electronic delay lines are also used. These consist of up to several thousand electronic capacitors connected in line in an integrated circuit. The signal is sampled at three times its highest frequency, and a charge corresponding to these samples is passed down the line. Their rate of progress is determined by pulses generated by an external clock. Thus the total delay can be altered by changing the clock frequency and multiple delays are obtained by tapping off at various points along the line. A mixture of various types of delay and reverberation applied at different points and to different instruments can often be found on the same record. Reverberation period The time required for the sound in an enclosure to decay to one millionth (60 dB) of its original intensity.