Waveformkódolás

Waveformkódolás, also known as waveform coding or speech coding, is a process used in telecommunications and digital signal processing to represent the analog waveform of a signal, typically speech, in a digital format. The primary goal is to reduce the amount of data required to represent the signal while maintaining acceptable quality. This is crucial for efficient transmission and storage of audio information.

There are several categories of waveform coding techniques. One broad category is waveform coding proper, which aims to accurately reproduce the original waveform as closely as possible. Examples include pulse-code modulation (PCM), which samples the analog signal at regular intervals and quantizes the amplitude of each sample. Differential pulse-code modulation (DPCM) and adaptive differential pulse-code modulation (ADPCM) are variations that encode the difference between consecutive samples, exploiting the correlation between them to achieve better compression.

Another approach is model-based coding, which uses a model of the signal's generation process. For speech, this often involves modeling the vocal tract and the excitation source (e.g., vocal cord vibrations). Linear predictive coding (LPC) is a well-known example, where past speech samples are used to predict the current sample. More advanced techniques, such as code-excited linear prediction (CELP), combine waveform matching with source modeling to achieve high compression ratios with good perceptual quality.

The choice of waveform coding technique depends on factors such as desired bit rate, acceptable distortion, and computational complexity. Lower bit rates are achieved by more aggressive compression, which can sometimes lead to audible artifacts. Waveform coding is fundamental to modern digital communication systems, including voice over IP (VoIP) and mobile phone networks.