quiet sounds were meant to be played back at low gain and loud sounds were meant to be played back at high gain, via automatic gain control in the playback equipment; this reduced the effect of surface noise on quiet passages). A similar and very short lived scheme involved using the CBS-developed "CX" noise reduction encoding/decoding scheme.
ELPJ, a Japanese-based company, has developed a player that uses a laser instead of a stylus to read vinyl discs. In theory the laser turntable eliminates the possibility of scratches and attendant degradation of the sound, but its expense limits use primarily to digital archiving of analog records. Various other laser-based turntables were tried during the 1990s, but while a laser reads the groove very accurately, since it does not touch the record, the dust that vinyl naturally attracts due to static charge is not cleaned from the groove, worsening sound quality in casual use compared to conventional stylus playback.
The normal commercial disc is engraved with two sound bearing concentric spiral grooves, one on each side of the disc, running from the outside edge towards the centre. Since the late 1910s, both sides of the record have been used to carry the grooves. The recording is played back by rotating the disc clockwise at a constant rotational speed with a stylus (needle) placed in the groove, converting the vibrations of the stylus into an electric signal (see magnetic cartridge), and sending this signal through an amplifier to loudspeakers.
The majority of music records are pressed on black vinyl. The colouring material used to blacken the transparent PVC plastic mix is carbon black, the generic name for the finely divided carbon particles produced by the incomplete burning of a mineral oil based hydrocarbon. Carbon black increases the strength of the disc and renders it opaque.