Overview of PCM File Format

Overview of PCM File Format

PCM file: the analog audio signal is directly formed by Analog-to-analog conversion (A/D conversion ).Binary SequenceThe file does not have an additional file header and end mark. Windows Convert can Convert PCM audio files to Microsoft WAV files.
Number of channels,Number of sampling digitsAndSampling frequency.

Sampling frequency:That is, the sampling frequency, which refers to the number of times the sound sample is obtained per second. The higher the sampling frequency, the better the sound quality, and the more authentic the sound is, but at the same time it occupies more resources. Because the resolution of human ears is very limited, it cannot be determined at a too high frequency. There are several levels of 16-bit sound cards, such as 22 KHz and 44 KHz. Among them, 22 KHz is equivalent to the sound quality of common fmbroadcast, and 44 KHz is equivalent to the CD sound quality. Currently, the common sampling frequency is no more than 48 KHz.
Number of sampling digits: the sampling value or sampling value (that is, the sample amplitude is quantified ). It is a parameter used to measure the fluctuation of sound, or the resolution of the sound card. The larger the value, the higher the resolution, and the stronger the sound.
Number of audio channels: it is easy to understand. There are two channels: single-channel and stereo. A single-channel sound can only use one speaker to generate a sound. (Some also process two speakers to output the same sound channel ), the PCM of the stereo sound can make both speakers speak out (generally there is a division of work in the left and right channels), and the space effect can be better felt.

Next, let's look at the concepts of the number of sampling digits and the sampling frequency. Let's take a look at these images. The black curve in the figure represents the natural acoustic waves recorded by the PCM file, the red curve represents the acoustic waves output by the PCM file, the horizontal coordinate is the sampling frequency, and the ordinate coordinate is the number of sampling digits. The grids in these images are gradually encrypted from left to right. First, the density of the horizontal coordinates is increased, and then the density of the vertical coordinates is increased. Obviously, the smaller the unit of the abscissa, that is, the smaller the interval between the two sampling points, the more favorable it is to keep the original sound. In other words, the higher the sampling frequency, the more assured the sound quality; similarly, the smaller the ordinate unit, the more favorable the sound quality, that is, the larger the number of sampling digits, the better.

Generally, the number of sampling digits in a computer is divided into 8-bit and 16-bit, but note that the 8-bit values do not mean dividing the ordinate coordinates into eight portions, but dividing them into 256 portions to the power of two; similarly, the 16-bit system divides the ordinate coordinates into 65536 portions of the 16 power. The sampling frequencies include 11025 HZ (11 KHz), 22050 HZ (22 KHz), and 44100Hz (44 KHz) three.

Now we can get the formula for the capacity occupied by PCM files: storage capacity = (sampling frequency * sampling digit * channel) * time/8 (unit: bytes ).
(44.1*1000 * l6 * 2) * 60/8 = 10,584,000 (bytes) = 10.584MBytes. This value is the storage space occupied by PCM audio files on the hard disk.