Sound Enhancements

(that's a double entendre, get it?)

As the LP became established as the dominant size for longer recordings, several developments were made to enhance the sound.

High fidelity

The first of these was the attempt to develop high fidelity, or hi-fi, sound. People who were concerned with hearing all the quality sound now embedded in the new LPs began to buy separate turntables, amplifiers, speakers and woofers to get the best sound possible. Stan Freberg satirized these fans in his 1956 radio show with a skit about a man who turned his whole house into a speaker.

Stereo sound

In 1958 the first stereo two-channel records were issued—by Audio Fidelity in the USA and Pye in Britain, using the Westrex "45/45" single-groove system. While the stylus moves horizontally when reproducing a monophonic disk recording, on stereo records the stylus moves vertically as well as horizontally.

One could envision a system in which the left channel was recorded laterally, as on a monophonic recording, with the right channel information recorded with a "hill-and-dale" vertical motion; such systems were proposed but not adopted, due to their incompatibility with existing phono pickup designs (see below). In the Westrex system, each channel drives the cutting head at a 45 degree angle to the vertical. During playback the combined signal is sensed by a left channel coil mounted diagonally opposite the inner side of the groove, and a right channel coil mounted diagonally opposite the outer side of the groove.

It is helpful to think of the combined stylus motion in terms of the vector sum and difference of the two stereo channels. Effectively, all horizontal stylus motion conveys the L+R sum signal, and vertical stylus motion carries the L-R difference signal. The advantages of the 45/45 system are:

    * greater compatibility with monophonic recording and playback systems. A monophonic cartridge will reproduce an equal blend of the left and right channels instead of reproducing only one channel. (However many monophonic styli would damage a stereo groove, leading to the common recommendation to never use a mono cartridge on a stereo record.) Conversely, a stereo cartridge reproduces the lateral grooves of monophonic recording equally through both channels, rather than one channel. 

     * a more balanced sound, because the two channels have equal fidelity (rather than providing one higher-fidelity laterally recorded channel and one lower-fidelity vertically recorded channel);

    * higher fidelity in general, because the "difference" signal is usually of low power and thus less affected by the intrinsic distortion of hill-and-dale recording.

This system was invented by Alan Blumlein of EMI in 1931 and patented the same year. EMI cut the first stereo test discs using the system in 1933. It was not used commercially until a quarter of a century later.

Stereo sound provides a more natural listening experience where the spatial location of the source of a sound is, at least in part, reproduced.

Other enhancements

Under the direction of C. Robert Fine, Mercury Records initiated a minimalist single microphone monaural recording technique in 1951. The first record, Kubelik/Chicago's performance of "Pictures at an Exhibition" was described as "being in the living presence of the orchestra" by The New York Times music critic. The series of records was then named “Mercury Living Presence”. In 1955 Mercury began three-channel stereo recordings, still based on the principle of the single microphone. The center (single) microphone was of paramount importance, with the two side mics adding depth and space. Record masters were cut directly from a three-track to two-track mixdown console, with all editing of the master tapes done on the original three-tracks. In 1961 Mercury enhanced this technique with three-microphone stereo recordings using 35 mm magnetic film instead of half-inch tape for recording. The greater thickness and width of 35 mm magnetic film prevented tape layer print-through and pre-echo and gained extended frequency range and transient response. The Mercury Living Presence recordings were remastered to CD in the 1990s by the original producer, using the same method of 3-to-2 mix directly to the master recorder.

The development of quadraphonic records was announced in 1971. These recorded four separate sound signals. This was achieved on the two stereo channels by electronic matrixing, where the additional channels were combined into the main signal. When the records were played, phase-detection circuits in the amplifiers were able to decode the signals into four separate channels. There were two main systems of matrixed quadraphonic records produced, confusingly named SQ (by CBS) and QS (by Sansui). They proved commercially unsuccessful, but were an important precursor to later "surround sound" systems, as seen in SACD and home cinema today. A different format, CD-4 (not to be confused with compact disc), by RCA, encoded rear channel information on an ultrasonic carrier, which required a special wideband cartridge to capture it on carefully-calibrated pickup arm/turntable combinations. Typically the high frequency information inscribed onto these LPs wore off after only a few playings, and CD-4 was even less successful than the two matrixed formats.

In the late 1970s and 1980s, a method to improve the dynamic range of mass produced records involved highly advanced disc cutting equipment. These techniques, marketed as the CBS DisComputer and Teldec Direct Metal Mastering, were used to reduce inner-groove distortion. RCA Victor introduced another system to boost dynamic range and achieve a groove with less surface noise under the commercial name of Dynagroove. Two main elements were combined: another disk material with less surface noise in the groove and dynamic expansion for masking background noise. Sometimes this was called "diaphragming" the source material and not favoured by some music lovers for its unnatural side effects. Both elements were reflected in the brandname of Dynagroove, described elsewhere in more detail. Furthermore it used advanced forward looking steering on track distance with respect to volume of sound and position on the disk. Tracks were close to each other with lower volumes and farther away with loud passages. Also the higher track density at lower volumes enabled disk recordings to end farther away from the inner circle than usual, helping to reduce endtrack distortion even further.

Also in the late 1970s, "direct-to-disc" records were produced, aimed at an audiophile niche market. These completely bypassed the use of magnetic tape in favor of a "purist" transcription directly to the master lacquer disc. Also during this period, "half-speed mastered" and "original master" records were released, using expensive state-of-the-art technology. A further late 1970s development was the Disco Eye-Cued system used mainly on Motown 12-inch singles released between 1978 and 1980. The introduction, drum-breaks or choruses of a track were indicated by widely separated grooves, giving a visual clue to DJs mixing the records. The appearance of these records is similar to an LP, but they only contain one track each side.

The early 1980s saw the introduction of "dbx-encoded" records, again for the audiophile niche market. These were completely incompatible with standard record playback preamplifiers, relying on the dbx compandor encoding/decoding scheme to greatly increase dynamic range (dbx encoded disks were recorded with the dynamic range compressed by a factor of two in dB: 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.