PCM (Pulse-Code Modulation) - definition
PCM (Pulse-Code Modulation) - definition
PCM (Pulse-Code Modulation) is a technique of digital modulation of an analogue signal, which involves sampling the signal at specified intervals and then representing each sample by a binary code. It is one of the basic and most widely used methods of converting analogue signals into digital form, used in telecommunications systems, audio recording, data transmission and digital signal processing, among others.
The PCM process consists of three main stages: sampling, quantisation and encoding. In the first stage, the analogue continuous signal is measured at fixed intervals according to the sampling frequency, which, according to the Nyquist theorem, must be at least twice the highest frequency of the source signal. Each sample is then quantised, i.e. rounded to the nearest value from a fixed set of levels, and finally each of these values is encoded as a sequence of bits.
PCM is an uncompressed technique, meaning that the data is recorded in its full digital form, with no reduction of information. For this reason, it provides a very high fidelity reproduction of the original signal, but at the same time generates large amounts of data. Standard applications such as CD-Audio discs use sampling at 44.1 kHz and 16-bit resolution, which allows for accurate sound reconstruction.
PCM provides the foundation for more complex signal coding methods such as DPCM (Differential PCM) or ADPCM (Adaptive Differential PCM), which use correlations between samples to reduce the amount of data transmitted. PCM is widely used in digital telephony (e.g. E1/T1 systems), the audio and video industry, as well as in medical and industrial signal recording and transmission systems. Due to the deterministic nature of this modulation, PCM-encoded signals are easy to process and resistant to noise in digital transmission channels.
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