PCM [ Pulse Code Modulation ] Pulse Code Modulation
PCM is one of the methods to convert analog signals such as voice into digital data. A sample of signal strength at regular intervals. If you save it as is, it will be uncompressed data.
PCM
The analog signal strength is measured at regular intervals according to the sampling rate and quantized as an integer value within a specific number of bits. For example, audio from a CD is recorded at a 44.1 kHz (kilohertz) sample rate and 16-bit quantization, which measures signals 44,100 times per second and represents their intensity in 65,536 (2 16 ) steps.
Higher quality data can be obtained by increasing the sampling rate and the number of quantization bits, but the amount of data increases accordingly. According to the sampling theorem, signals up to half the sampling frequency can be reproduced, which is called the Nyquist frequency. In the case of speech, it is known that the upper limit of human audible sound is about 20 kHz, and it is said that if a sampling frequency higher than 40 kHz is used, it will be possible to reproduce a near-natural sound from the recorded data.
The normal PCM method is also called linear PCM (LPCM), which is a format in which the data obtained by each sampling is ordered, but the difference registration method In addition, a method for adaptively changing the number of quantization bits of each DPCM sample according to the fluctuation range of the immediately previous sample is called ADPCM (Adaptive Defferential PCM). This is often used in practice because it can reduce the amount of data after encoding while maintaining almost the same quality as PCM.
