PCM Full Form – Pulse-Code Modulation

PCM Full Form

PCM Full Form – Pulse-Code Modulation

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals.

Pulse code modulation is a method that is used to convert an analog signal into a digital signal so that a modified analog signal can be transmitted through the digital communication network.

 

It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications.

LPCM is used for the lossless encoding of audio data in the Compact disc Red Book standard (informally also known as Audio CD), introduced in 1982.

 

PCM is in binary form, so there will be only two possible states high and low(0 and 1).

On PCs, PCM and LPCM often refer to the format used in WAV (defined in 1991) and AIFF audio container formats (defined in 1988).

 

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.

RF64 container format (defined in 2007) uses LPCM and also allows non-PCM bitstream storage: various compression formats contained in the RF64 file as data bursts can be “disguised” as PCM linear.

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 μ-law algorithm).

LPCM is used by HDMI (defined in 2002), a single-cable digital audio/video connector interface for transmitting uncompressed digital data.

Though PCM is a more general term, it is often used to describe data encoded as LPCM.

It is also defined as a part of various digital video and audio storage formats (e.g. DV since 1995, AVCHD since 2006[27]).

PCM Full Form – Pulse-Code Modulation

 

LPCM has been defined as a part of the DVD (since 1995) and Blu-ray (since 2006) standards.

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.

PCM is the method of encoding typically used for uncompressed digital audio.

This development improved capacity and call quality compared to the previous frequency-division multiplexing schemes.

AES3 (specified in 1985, upon which S/PDIF is based) is a particular format using LPCM.
LaserDiscs with digital sound have an LPCM track on the digital channel.

In 1973, adaptive differential pulse-code modulation (ADPCM) was developed, by P. Cummiskey, Nikil Jayant and James L. Flanagan.

LPCM data may also be stored in other formats such as AU, raw audio format (header-less file) and various multimedia container formats.

The T-carrier system, introduced in 1961, uses two twisted-pair transmission lines to carry 24 PCM telephone calls sampled at 8 kHz and 8-bit resolution.

The 4ESS switch introduced time-division switching into the US telephone system in 1976, based on medium scale integrated circuit technology.

Electrical engineer W. M. Miner, in 1903, used an electro-mechanical commutator for time-division multiplexing multiple telegraph signals; he also applied this technology to telephony.

PCM Full Form – Pulse-Code Modulation

 

Early electrical communications started to sample signals in order to multiplex samples from multiple telegraphy sources and to convey them over a single telegraph cable.

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.

Another patent by the same title was filed by John R. Pierce in 1945, and issued in 1948: U.S. Patent 2,437,707. The three of them published “The Philosophy of PCM” in 1948.

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.

PCM Full Form – Pulse-Code Modulation

 

British engineer Alec Reeves, unaware of previous work, conceived the use of PCM for voice communication in 1937 while working for International Telephone and Telegraph in France.

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”.

The American inventor Moses G. Farmer conveyed telegraph time-division multiplexing (TDM) as early as 1853.

 

He obtained intelligible speech from channels sampled at a rate above 3500–4300 Hz; lower rates proved unsatisfactory.

The plate collected or passed the beam, producing current variations in binary code, one bit at a time.
U.S. Patent 2,801,281 filed in 1946 and 1952, granted in 1956.

The first transmission of speech by digital techniques, the SIGSALY encryption equipment, conveyed high-level Allied communications during World War II.

PCM Full Form – Pulse-Code Modulation

 

Rather than natural binary, the grid of Goodall’s later tube was perforated to produce a glitch-free Gray code and produced all bits simultaneously by using a fan beam instead of a scanning beam.

By this time Reeves had started working at the Telecommunications Research Establishment.

In 1949, for the Canadian Navy’s DATAR system, Ferranti Canada built a working PCM radio system that was able to transmit digitized radar data over long distances.

 

In 1943 the Bell Labs researchers who designed the SIGSALY system became aware of the use of PCM binary coding as already proposed by Reeves.

As in an oscilloscope, the beam was swept horizontally at the sample rate while the vertical deflection was controlled by the input analog signal, causing the beam to pass through higher or lower portions of the perforated plate.

PCM in the late 1940s and early 1950s used a cathode-ray coding tube with a plate electrode having encoding perforations.

He described the theory and its advantages, but no practical application resulted. Reeves filed for a French patent in 1938, and his US patent was granted in 1943.

PCM Full Form – Pulse-Code Modulation

 

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