Fidelity and Formats
The audio quality of LPs increased greatly over time. Some significant advances in LP landmarks are:
- Stereo sound, 1958
- Helium-cooled cutting heads that could withstand higher levels of high frequencies (Neumann SX68) – previously, the cutting engineer had to reduce the HF content of the signal sent to the record cutting head, otherwise the delicate coils could burn out
- Elliptical Stylus (marketed by several manufacturers at the end of the 60s)
- Cartridges that operate at lower tracking forces of circa 2 grams, beginning from mid-60s
- Half speed and 1/3 speed record cutting, which extend the usable bandwidth of the record
- Matrixed quadraphonic records (SQ, QS, EV-4, UHJ)
- "Discrete" quadraphonic CD4 records, which enabled frequencies of up to 50 kHz to be recorded and played back
- Longer-lasting, antistatic record compounds (ex: RCA Dynaflex, Q-540)
- Better stylus tip shapes (Shibata, Van den Hul, MicroLine, etc.)
- Direct Metal Mastering
- Noise-reduction (CX encoding, DBX encoding), starting from 1973
Early LP recordings were monaural, but stereo LP records became commercially available in 1958. In the 1970s, quadraphonic sound (four-channel) records became available. These did not achieve the popularity of stereo records, partly because of scarcity of consumer playback equipment, competing and incompatible quad record standards (each of which were compatible with two-channel stereo equipment) and partly because of the lack of quality in quad-remix releases. Quad never escaped the reputation of being a "gimmick". Three-way and quadraphonic recordings, which were favored and championed by artists like Leopold Stokowski and Glenn Gould, are now making a modest comeback, with older masters being turned into multi-channel Super Audio CDs. (However, a fair number of new surround recordings—primarily classical—are being made for SACD and Blu-ray Audio.)
The composition of vinyl used to press records has varied considerably over the years. Virgin vinyl is preferred, but during the 1970s energy crisis, it became commonplace to use recycled vinyl – melted unsold records with all of the impurities. Sound quality suffered, with increased ticks, pops and other surface noises. Other experiments included reducing the thickness of LPs, leading to warping and increased susceptibility to damage. Using a bead of 130 grams of vinyl had been the standard, but some labels experimented with as little as 90 grams per LP. Today, high fidelity pressings follow the Japanese standard of 160, 180 or 200 grams.
Besides the standard black vinyl, specialty records are also pressed on different colors of PVC or special "picture discs" with a card picture sandwiched between two clear sides. Records in different novelty shapes are also produced.
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