Digital_Audio

Moscow State University the Faculty of Computational Mathematics and Cybernetics Digital Audio Student: Rodionov Pavel Group: 111 Contents Introduction 3 1 Overview of digital audio 3 2 Subjective evaluation 5 3 History of digital audio use in commercial recording 5 4 Digital audio workstation 5 Conclusion 6 Abbreviations 7 References 7 Introduction Digital audio has emerged because of its usefulness in the recording, manipulation, mass-production, and distribution of sound. Modern distribution of music across the internet through on-line stores depends on digital recording and digital compression algorithms. Distribution of audio as data files rather than as physical objects has significantly reduced costs of distribution. From the wax cylinder to the compact cassette, analogue audio music storage and reproduction have been based on the same principles upon which human hearing are based. In an analogue audio system, sounds begin as physical waveforms in the air, are transformed into an electrical representation of the waveform, via a transducer (for example, a microphone), and are stored or transmitted. To be re-created into sound, the process is reversed, through amplification and then conversion back into physical waveforms via a loudspeaker. Although its nature may change, its fundamental wave-like characteristics remain unchanged during its storage, transformation, duplication, and amplification. All analogue audio signals are susceptible to noise and distortion, due to the inherent noise present in electronic circuits. In other words, all distortion and noise in a digital signal are added at capture or processing, and no more is added in repeated copies, unless the entire signal is lost, while analog systems degrade at each step, with each copy, and in some media, with time, temperature, and magnetic or chemical issues. Digital audio is the method of representing audio in digital form. An analog signal is converted to a digital signal at a given sampling rate and bit resolution; it may contain multiple channels (2 channels for stereo or more for surround sound). Generally speaking: the higher the sampling rate and bit resolution the more fidelity, as well as increase the amount of digital data. Sound quality While the goal of both analogue and digital systems is to reproduce audio perfectly, there are several obstacles to achieving this, including: Analogue noise floor in the capturing circuitry has inherent capacitance and inductance that limits the bandwidth of the system, and resistance that limits the amplitude. Digital quantization noise in the capturing circuitry, and sampling rate limits the bandwidth and its bit resolution limits the dynamic range (resolution of amplitude creation). In order to achieve better fidelity, higher quality components are required, which increases overall cost. Conversion process Some audio signals such as those created by digital synthesis originate entirely in the digital domain, in which case analog to digital conversion does not take place. After being sampled with the ADC, the digital signal may then be altered in a process which is called digital signal processing where it may be filtered or have effects applied. The digital audio signal may then be stored or transmitted. Digital audio storage can be on a CD, a digital audio player, a hard drive, USB flash drive, CompactFlash, or any other digital data storage device. Audio data compression techniques — such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC — are commonly employed to reduce the file size. Digital audio can be streamed to other devices. The last step for digital audio is to be converted back to an analog signal with a digital-to-analog converter (DAC). Like ADCs, DACs run at a specific sampling rate and bit resolution but through the processes of oversampling, upsampling, and downsampling, this sampling rate may not be the same as the initial sampling rate. Fidelity evaluation is a long-standing issue with audio systems in general and introduction of lossy compression algorithms and psychoacoustic models has only increased debate. Audio can be measured and analyzed more precisely than can be done manually by listening to the content, but what this technical measurement and analysis lacks is the ability to determine if it sounds "good" or "bad" to any given listener. Like any other human opinion, there are numerous parameters that widely vary between people that affect their subjective evaluation of what is good or bad. Such things that pertain to audio include hearing capabilities, personal preferences, location with respect to the speakers, and the room's physical properties. This is not to say that subjective evaluation is unique to digital audio; digital audio can add to the fervor of discussion because it does introduce more things (e.g., lossy compression, psychoacoustic models) that can be debated. History of digital audio use in commercial recording Commercial digital recording of classical and jazz music began in the early 1970s, pioneered by Japanese companies such as Denon, the BBC, and British record label Decca (who in the mid-70s developed digital audio recorders of their own design for mastering of their albums), although experimental recordings exist from the 1960s. The first 16-bit PCM recording in the United States was made by Thomas Stockham at the Santa Fe Opera in 1976 on a Soundstream recorder. In most cases there was no mixing stage involved; a stereo digital recording was made and used unaltered as the master tape for subsequent commercial release. These unmixed digital recordings are still described as DDD since the technology involved is purely digital. (Unmixed analogue recordings are likewise usually described as ADD to denote a single generation of analogue recording.) Although the first-ever digital recording of a non-classical music piece, Morrissey-Mullen's cover of the Rose Royce hit "Love Don't Live Here Anymore" (released 1979 as a vinyl EP) was recorded in 1978 at EMI's Abbey Road recording studios, the first entirely digitally recorded (DDD) popular music album was Ry Cooder's Bop Till You Drop, recorded in late 1978. It was unmixed, being recorded straight to a two-track 3M digital recorder in the studio. Many other top recording artists were early adherents of digital recording. Digital audio workstation {draw:frame} A digital audio workstation (DAW) is an electronic system designed to record, edit and play back digital audio. A key feature of DAWs is the ability to freely manipulate recorded sounds. Many DAWs, especially computer-based DAWs, have MIDI recording, editing, and playback capabilities. The term "DAW" simply refers to a general combination of audio multitrack software and high-quality audio hardware — the latter being a specialized audio converter unit which performs some variety of analog-to-digital (ADC) and/or digital-to-analog (DAC) signal conversion. For example, a workstation could have eight discrete audio inputs, and two or more audio outputs for playback monitoring or routing signal to other devices. Systems can have as few as two mono inputs and outputs; the discrete audio inputs and outputs provide for simultaneous multitracking dual mono sources or stereo recording. A professional DAC performs the same function as a common sound card, but is generally of higher quality and offers sonic or functional advantages when compared with its consumer cousin. While almost any home computer with multitrack and editing software can function somewhat as a DAW, the term generally refers to computer systems which have high-quality external ADC-DAC hardware, and some form of audio software; some of which is commercial proprietary software. Besides having high-end sound cards most DAWs also require a large amount of RAM, fast CPU(s) and sufficient free hard drive space. Development Musicians and composers long had a desire to integrate stereos, turntables, recording equipment, MIDI keyboards and even electric guitars with computers. Serious computer-based composition tools began to appear with the Atari ST and Amiga computer systems. Enthusiasts continued to seek more integrated, easier-to-use and higher-performance tools for audio creation tasks. Many current DAWs even support integration with video streams allowing full A/V production. Conclusion Digital audio is a new generation of audio usage. The previous one was using audio CDs for distribution of music or spoken word content. So the first step towards the digital audio heaven would be to rip that CD, creating a digital copy of the song and storing it on the computer’s hard drive. There are many ways of doing that and nowadays most music player software comes with the feature built in. For example, iTunes. Digital audio has become an important part of our lives. The Internet has played a big role in making it mainstream and more accessible than ever. There are various formats that suite different needs and purposes, but still they have their limitations due to being closed and proprietary. Maybe creating an open standard that everyone would support could be a good thing, just as HTML has become a basis for the Web. In that case everyone would be able to contribute and innovate making the digital audio progress that much greater to the benefit of others. Abbreviations ADC - Analog-to-Digital Converter DAC - Digital-to-Analog Converter ADD - ADD, a SPARS code appearing on some compact disc recordings, telling the consumer that the recording was made on analog (A) equipment and digital (D) equipment was used to mix/edit and master the recording DAW - Digital Audio Workstation References http://ilyashmorgun.wordpress.com/2009/09/29/essay-on-introduction-to-audio-theory-and-digital-audio/ http://digital-audio.suite101.com/article.cfm/what_is_daw_software http://en.wikipedia.org/wiki/Digital_audio