From the fundamentals of digital audio to its application
Introduction: There are specifications, characteristics and unique properties of digital technology.
The name digital audio has quickly penetrated the market since the launch of CD players and audio CDs (hereinafter referred to as “CDDA” in this series) in 1982. Before that, audio sources (media recording) were LP records and magnetic tapes, and turntables and tape recorders were the core of audio playback equipment. After the advent of CDDA, MD (Mini Disc) and DAT (Digital Audio Tape) were developed as digital audio applications. In addition, SACD (Super Audio CD), DVD and Blu-ray have appeared, and recently, audio playback in file formats such as MP3, PC / USB audio, and Internet audio has become widespread.
The core technologies of digital audio are AD (analog to digital) conversion and DA (digital to analog) conversion. As long as it is audio, there is no doubt that the quality of the analog signal is important. However, digital audio has specifications, characteristics, and properties of digital audio that are different from conventional analog audio, and most of them are concentrated in the DA conversion system in the playback system.
Digital audio is a technology that has already been put into practice and is widely used in various devices. For this reason, some may point to “what happens now”. However, there are few cases where it is precisely and essentially explained. In this series titled “From the Basics to Digital Audio Applications,” we plan to explain the theory, core technology, applied technology, and unique mounting technology of digital audio in detail from this perspective. First, in Part 1 and Part 2, we will introduce the differences between analog audio and digital audio, and the points to keep in mind when understanding digital audio signals.
What is digital audio in the first place?
Similar to a general electrical signal, the characteristics of a conventional analog audio signal are defined by “signal level” and “signal frequency”. In the reproduction of an analog source, the signals that are handled with the exception of the control system are completely analog signals, and the main characteristics of the analog signals are applied as is. Figure 1 shows the general image of the analog audio reproduction system. Representatives of music sources are LP records and magnetic tapes (open reels, cassettes), and record players (including cartridges) and decks are used as electrical signal conversion and reproduction devices. The noise at each stage of signal processing determines the dynamic range as the ratio of signal to noise.
On the other hand, in digital audio, the source of the signal is a digital signal. The digital signal has digital information according to the signal level and the frequency of the original analog signal. At the same time, it has “digital signal characteristics”. The properties of a digital signal are the “quantization bit number” (quantization resolution, also expressed as “M bit”) that defines the information of the amplitude axis and the “sample rate” (sample rate, fs) which defines the frequency axis information. ) It is also expressed).
