1.6. Audio Coding

At present, there is no single standard coding system for audio information, since the methods and methods of working with audio information have begun to develop in comparison with the methods of working with other types of information with the most recent ones. Therefore, many different companies that work in the field of information coding have created their own corporate standards for audio information. But among these corporate standards, there are two main areas.

The FM (Frequency Modulation) method is based on the statement that theoretically any complex sound can be represented as a decomposition into a sequence of the simplest harmonic signals of different frequencies. Each of these harmonic signals is a regular sine wave and therefore can be described by numeric parameters or encoded. The audio signals form a continuous spectrum, i.e., are analog, therefore their decomposition into harmonic series and representation in the form of discrete digital signals is performed using special devices - analog-to-digital converters (ADC). The inverse transform, which is necessary to reproduce sound encoded by a numeric code, is performed using digital-to-analog converters (D / A). Due to such transformations of audio signals, there are losses of information associated with the encoding method, therefore the quality of sound recording using the FM method is usually not satisfactory and corresponds to the sound quality of the simplest electromusical instruments with a color characteristic of electronic music. At the same time, this method provides a quite compact code, so it was widely used in those years when the resources of computer equipment were clearly insufficient.

The basic idea of the wave-table synthesis method (Wave-Table) is that in the previously prepared tables there are samples of sounds for many different musical instruments. These sound samples are called samples. The numerical codes that are embedded in the sample express such characteristics as the type of instrument, its model number, pitch, duration and intensity of sound, its dynamics, some components of the environment in which the sound is observed, and other parameters characterizing the characteristics of the sound. Since real sounds are used for the samples, the quality of the encoded sound information is very high and approaches the sound of real musical instruments, which is more consistent with the current level of development of modern computer technology.