La Wikipedia dice en inglés porque en castellano poco cuenta:
Sobre los vinilos
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Frequency response and noise
In 1925, electric recording extended the recorded frequency range from acoustic recording (168–2000 Hz) by 2½ octaves to 100–5000 Hz. Even so, these early electronically recorded records used the exponential-horn phonograph (see Orthophonic Victrola) for reproduction.
The frequency response of vinyl records may be degraded by frequent playback if the cartridge is set to track too heavily, or the stylus is not compliant enough to trace the high frequency grooves accurately, or the cartridge/tonearm is not properly aligned. The RIAA has suggested the following acceptable losses: down to 20 kHz after one play, 18 kHz after three plays, 17 kHz after five, 16 kHz after eight, 14 kHz after fifteen, 13 kHz after twenty five, 10 kHz after thirty five, and 8 kHz after eighty plays. While this degradation is possible if the record is played on improperly set up equipment, many collectors of LPs report excellent sound quality on LPs played many more times when using care and high quality equipment. This rapid sound degradation is not usually typical on modern Hi-Fi equipment with a properly balanced tonearm and well balanced low-mass stylus.
CD-4 LPs contain two sub-carriers, one in the left groove wall and one in the right groove wall. These sub-carriers use special FM-PM-SSBFM (Frequency Modulation-Phase Modulation-Single Sideband Frequency Modulation) and have signal frequencies that extend to 45 kHz. It should be noted that CD-4 sub-carriers could be played with any type stylus as long as the pickup cartridge had CD-4 frequency response. The recommended Stylus for CD-4 as well as regular stereo records was a line contact or Shibata type.
Gramophone sound suffers from rumble, low-frequency (below about 30 Hz) mechanical noise generated by the motor bearings and picked up by the stylus. Equipment of modest quality is relatively unaffected by these issues, as the amplifier and speaker will not reproduce such low frequencies, but high-fidelity turntable assemblies need careful design to minimize audible rumble.
Room vibrations will also be picked up if the pedestal—turntable—pickup arm—stylus system is not well damped.
Tonearm skating forces and other perturbations are also picked up by the stylus. This is a form of frequency multiplexing as the "control signal" (restoring force) used to keep the stylus in the groove is carried by the same mechanism as the sound itself. Subsonic frequencies below about 20 Hz in the audio signal are dominated by tracking effects, which is one form of unwanted rumble ("tracking noise") and merges with audible frequencies in the deep bass range up to about 100 Hz. High fidelity sound equipment can reproduce tracking noise and rumble. During a quiet passage, woofer speaker cones can sometimes be seen to vibrate with the subsonic tracking of the stylus, at frequencies as low as about 0.5 Hz (the frequency at which a 33⅓ rpm record turns on the turntable). Another reason for very low frequency material can be a warped disk: its undulations produce frequencies of only a few hertz and presentday amplifiers have large power bandwidths. For this reason, many stereo receivers contained a switchable subsonic filer. Some subsonic content is directly out of phase in each channel. If played back on a mono subwoofer system, the noise will cancel, significantly reducing the amount of rumble that is reproduced.
At high audible frequencies, hiss is generated as the stylus rubs against the vinyl, and from dirt and dust on the vinyl. Noise can be reduced somewhat by cleaning the record prior to playback.
Another method, introduced by the Lenco company is playing the disk "wet". Using a special dispenser the groove is wetted ahead of the stylus passing by and dries up afterwards. This certainly reduces hiss, but when it became clear that any disk once played wet, should forever be played this way because of residue left behind, people did not change over in great numbers. With normal cleaning this problem does not occur (this also seems to remove Lenco residue if present).
Y sobre el CD-4 LPs (sonido cuadrafónico)
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Compatible Discrete 4 (CD-4) or Quadradisc (not to be confused with compact disc) was introduced in 1971 as a discrete quadraphonic system created by JVC. Record companies who adopted this format include Arista, Atlantic, Capricorn, Elektra, Fantasy, JVC, Nonesuch, RCA, Reprise and Warner.
This was the only fully discrete Quadraphonic Phonograph record system to gain major industry acceptance.
In the CD-4 system, the Quadraphonic audio was divided into Left and Right channels with the Left recorded on one groove wall and the Right on the other, which is the case with normal stereo. The audio frequencies (20Hz to 15KHz), often referred to as the sum channel, would contain the sum of the Left Front plus Left Back signals in the Left channel and the sum of the Right Front plus the Right Back signals in the Right channel. In other words, if you looked at the audio frequencies only, you had an ordinary stereo recording. Along with this audio, a separate 30KHz sub-carrier was recorded on each groove wall. The sub-carrier on each side carried the difference signal for that side. This was the information that enabled a combined signal to be resolved into two separate signals. For the Left sub-carrier it would be Left Front minus Left Back, and for the Right sub-carrier it would be the Right Front minus the Right Back. These audio signals were modulated onto the carriers using a special FM-PM-SSBFM (Frequency Modulation-Phase Modulation-Single Sideband Frequency Modulation) technique. This created an extended sub-carrier frequency range from 18 kHz to 45 kHz for the left and right channels. The algebraic addition and subtraction of the sum and difference signals would then yield compatible and discrete Quadraphonic playback. CD-4 was responsible for major improvements in phonograph technology including better compliance, lower distortion levels, pick-up cartridges with a significantly higher frequency range, and new record compounds such as Q-540, which were highly anti-static. Also a direct by-product of CD-4 technology was the Shibata contact stylus. Invented by Dr. Norio Shibata, the Shibata stylus greatly increased the contact area on the groove walls, which in turn reduced wear over time, thus maintaining the original LP's fidelity and frequency range for much longer than normal. This, of course, prolonged the overall playable life of a record – a definite boon for any audiophile or serious record collector. But what was (arguably) even more impressive was that the Shibata stylus was also capable of recovering sizeable portions of program audio that would otherwise be compromised or lost on a damaged or scratched disc (audio that a standard, non-CD-4-compatible stylus would fail to pick up). A typical CD-4 system would have a turntable with a CD-4 cartridge, a CD-4 demodulator, a discrete four-channel amplifier, and (ideally) four full-range loudspeakers. Some manufactures built the CD-4 demodulator into complete four-channel receivers.
Simply put, CD-4 consists of four recorded signals (LF, LB, RB, RF) and the following coding matrix.
The CD-4 encoding/decoding matrix:
* (LF+LB)+(LF-LB)=2LF or Left Front
* (LF+LB)-(LF-LB)=2LB or Left Back
* (RF+RB)+(RF-RB)=2RF or Right Front
* (RF+RB)-(RF-RB)=2RB or Right Back
Although CD-4 (and Quadraphonic audio in general) failed due to late FCC approval of FM Quadraphonic broadcasting, the improvements CD-4 engendered spilled over into, and substantially improved, the production of conventional stereo LP records.
Igualmente, aunque esos discos sean capaces de albergar hasta 50kHz, ¿donde los reproducirias y como? Y si lo hubiera, ¿existe algún micro de medición que pueda medir eso?
¿Para que valen esas frecuencias que nadie humano oye ni aunque tuviesen ese sistema cuadrafonico?
¿Un plato de batería llega a 50kHz? Puede ser, pero no hay micros que escuchen.
En fin, que yo lo veo como una curiosidad más que como algo a tener en cuenta.
, pero trasnochamos como si hubiesemos salido 
