Pulse Code Modulation (PCM) is the simplest form of waveform coding. Waveform coding is used to encode analogue signals (for example speech) into a digital. PCM is a digital scheme for transmitting analog data. Short for pulse code modulation, a sampling technique for digitizing analog signals, especially audio signals.


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  • Pulse Code Modulation (PCM)
  • What is pulse code modulation? Webopedia Definition
  • How pulse-code modulation helped win the war and create CDs
  • Pulse code modulation
  • Basic Elements of PCM
  • How pulse-code modulation helped win the war and create CDs

So rather than amplifying the whole signal, PCM regenerates by picking out individual pulses and sending new, clean pulses along the next length of cable — so the noise content of the signal is not increased.

Though Reeves patented his invention in the pulse code modulation s, PCM required circuitry that technology was not really up to delivering without hugely expensive effort.

This is why PCM was not used commercially until the s, when the invention of the transistor made it viable. The message signal is the signal which is being transmitted for communication and the carrier signal is a high frequency signal which pulse code modulation no data, but is used for long distance transmission.

What is Pulse Code Modulation (PCM)? - Definition from Techopedia

There are many modulation techniques, which are classified according to the type of modulation employed. A signal is pulse code modulated to convert its analog information into a binary sequence, i.

The output of a PCM will resemble a binary sequence. The following figure pulse code modulation an example of PCM output with respect to instantaneous values of a given sine wave. TDM is used more widely because of its natural compatibility with digital communication and its lower bandwidth requirement.

What is pulse code modulation (PCM)? - Definition from

After these pulse code modulation streams reach their destination, they are demultiplexed, broken back down into individual data streams, and demodulated, whereby the modulation procedure is applied in reverse to recreate the original binary numbers. These are further processed to restore the original analog waveform.

In the process of transitioning from one sampling period to the next, the signal gains significant high-frequency energy. pulse code modulation


This process is called quantization. The number of levels is always a power of 2 -- for example, 8, 16, 32, or A Pulse code modulation encoder performs three functions: Before converting the signal from analog to digital, the unwanted frequency components of the signal are filtered out.

This makes the task of converting the signal to digital form much pulse code modulation, and results in an acceptable quality of signal reproduction for voice communication.

Pulse code modulation (PCM)

From an equipment point of viev, because the manufacture of very precise filters would be expensive, a bandwidth of Hertz is generally used. This bandwidth limitation also helps to reduce aliasing pulse code modulation aliasing happens when the number of samples is insufficient to adequately represent the analog waveform the same effect you can see on a computer screen when diagonal and curved lines are displayed as a series of zigzag horizontal and vertical lines.

Sampling Sampling the analogue signal Sampling is the process of reading the values of the filtered analogue signal at discrete time intervals i.

A scientist called Harry Nyquist discovered that the original analogue signal could be reconstructed if enough samples were taken. He found that if the sampling frequency is pulse code modulation least twice the highest frequency of the input analogue signal, the signal could be reconstructed using a low-pass filter at the destination.

Quantisation Quantisation is the process of assigning a discrete value from a range of possible values to each sample obtained. The number of possible values will depend on the number of bits used to represent each sample. Quantisation can be achieved by either rounding the signal up or down to the neares available value, or truncating the signal to the pulse code modulation value which is lower than the actual sample.

The process results in a stepped waveform resembling the source signal.

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