In 1958 we were introduced to the stereo effects on phonographic records. The stereo consists of two separate channels of sound recorded in the same groove and given the name stereophonic, which still resident in the vinyl records of today. Just as the use of your two eyes creates a perception of depth, so can the effect of musical presence be achieved by stereophonic? Recording sounds with two appropriately positioned microphones and playing it back on two separated loudspeakers facilitate this. A stereo recording provides two separate signal channels as oscillations perpendicular to either one or the other of the faces of the record groove. These two signals are then fed into an audio amplifier through to the loudspeakers. The monaural pickup is replaced by one with two coils, which sense the motion of the stylus at right angles to each groove wall. The inside wall is used as the left channel and the outside wall the right. The set conditional criteria for frequency control of a recording are that the variation in frequency should not be perceptible to the ear. A frequency of about 0.1 percent is less than just the noticeable difference in frequency over most of the audible frequency range. In order to eliminate both slow variations in pitch of the recording, called wow, and rapid variations, known as flutter, the revolutionary speed of the record is carefully controlled by use of a reasonable weighted turntable and a meticulous precision motor and the automatic vibrations of the turntable are essentially secluded from the stylus to avoid rumble. In analogue systems, particularly tape systems, a measurement of the pitch shifting and pitch stability. Wow refers to slow shifts in pitch and flutter to faster, vibrato like fluctuations. |
