UP (abreviatura de): pulse-code modulation(eng)
TR (processo/parte de): Betacam (audio digital)(por)
TR (processo/parte de): Betacam Digital (audio digital)(por)
TR (processo/parte de): Betacam SP (audio digital)(por)
TR (processo/parte de): Betamax (audio digital)(por)
TR (processo/parte de): U-matic (audio digital)(por)
TR (processo/parte de): VHS (audio digital)(por)
TR (processo/parte de): Betacam (audio digital)(por)
TR (processo/parte de): Betacam Digital (audio digital)(por)
TR (processo/parte de): Betacam SP (audio digital)(por)
TR (processo/parte de): Betamax (audio digital)(por)
TR (processo/parte de): U-matic (audio digital)(por)
TR (processo/parte de): VHS (audio digital)(por)
Definição do conceito
[ENG] PCM | pulse-code modulation | Pulse-code modulation | Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. | Linear pulse-code modulation (LPCM) is a specific type of PCM in which the quantization levels are linearly uniform. This is in contrast to PCM encodings in which quantization levels vary as a function of amplitude (as with the A-law algorithm or the ?-law algorithm). Though PCM is a more general term, it is often used to describe data encoded as LPCM. | A PCM stream has two basic properties that determine the stream´s fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that can be used to represent each sample. | DIGITAL AUDIO RECORDINGS | In 1967, the first PCM recorder was developed by NHK´s research facilities in Japan. The 30 kHz 12-bit device used a compander (similar to DBX Noise Reduction) to extend the dynamic range, and stored the signals on a video tape recorder. In 1969, NHK expanded the system´s capabilities to 2-channel stereo and 32 kHz 13-bit resolution. In January 1971, using NHK´s PCM recording system, engineers at Denon recorded the first commercial digital recordings. | In 1972, Denon unveiled the first 8-channel digital recorder, the DN-023R, which used a 4-head open reel broadcast video tape recorder to record in 47.25 kHz, 13-bit PCM audio. In 1977, Denon developed the portable PCM recording system, the DN-034R. Like the DN-023R, it recorded 8 channels at 47.25 kHz, but it used 14-bits "with emphasis, making it equivalent to 15.5 bits." | In 1979, the first digital pop album, Bop till You Drop, was recorded. It was recorded in 50 kHz, 16-bit linear PCM using a 3M digital tape recorder. | The compact disc (CD) brought PCM to consumer audio applications with its introduction in 1982. The CD uses a 44,100 Hz sampling frequency and 16-bit resolution and stores up to 80 minutes of stereo audio per disc. | HISTORY | In 1920, the Bartlane cable picture transmission system used telegraph signaling of characters punched in paper tape to send samples of images quantized to 5 levels. In 1926, Paul M. Rainey of Western Electric patented a facsimile machine which transmitted its signal using 5-bit PCM, encoded by an opto-mechanical analog-to-digital converter. The machine did not go into production. | .../... | In the United States, the National Inventors Hall of Fame has honored Bernard M. Oliver and Claude Shannon as the inventors of PCM, as described in "Communication System Employing Pulse Code Modulation", U.S. Patent 2,801,281 filed in 1946 and 1952, granted in 1956. Another patent by the same title was filed by John R. Pierce in 1945, and issued in 1948: U.S. Patent 2,437,707. | NOMENCLATURE | The word "pulse" in the term "pulse-code modulation" refers to the pulses to be found in the transmission line. This perhaps is a natural consequence of this technique having evolved alongside two analog methods, pulse-width modulation and pulse-position modulation, in which the information to be encoded is represented by discrete signal pulses of varying width or position, respectively. In this respect, PCM bears little resemblance to these other forms of signal encoding, except that all can be used in time-division multiplexing, and the numbers of the PCM codes are represented as electrical pulses. | SOURCE : Pulse-code modulation Available at : https://en.wikipedia.org/wiki/Pulse-code_modulation Accessed : 27 nov. 2022
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