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The μ-law algorithm is a companding algorithm, primarily used in 8-bit PCM digital telecommunication systems in North America and Japan. It is one of the two companding algorithms in the G.711 standard from ITU-T, the other being the similar A-law. A-law is used in regions where digital telecommunication signals are carried on E-1 circuits, e.g. Europe.
Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or compressing an audio signal's dynamic range. Compression is commonly used in sound recording and reproduction, broadcasting, live sound reinforcement and some instrument amplifiers.
In acoustics, loudness is the subjective perception of sound pressure. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics.
An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon and is arrived at by reference to equal-loudness contours. By definition, two sine waves of differing frequencies are said to have equal-loudness level measured in phons if they are perceived as equally loud by the average young person without significant hearing impairment.
ReplayGain is a proposed technical standard published by David Robinson in 2001 to measure and normalize the perceived loudness of audio in computer audio formats such as MP3 and Ogg Vorbis. It allows media players to normalize loudness for individual tracks or albums. This avoids the common problem of having to manually adjust volume levels between tracks when playing audio files from albums that have been mastered at different loudness levels.
A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the signal level in audio equipment.
Audio normalization is the application of a constant amount of gain to an audio recording to bring the amplitude to a target level. Because the same amount of gain is applied across the entire recording, the signal-to-noise ratio and relative dynamics are unchanged. Normalization is one of the functions commonly provided by a digital audio workstation.
In digital and analog audio, headroom refers to the amount by which the signal-handling capabilities of an audio system can exceed a designated nominal level. Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via clipping. Standards bodies differ in their recommendations for nominal level and headroom.
Decibels relative to full scale is a unit of measurement for amplitude levels in digital systems, such as pulse-code modulation (PCM), which have a defined maximum peak level. The unit is similar to the units dBov and decibels relative to overload (dBO).
A peak programme meter (PPM) is an instrument used in professional audio that indicates the level of an audio signal.
ITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard, now referred to as ITU-R BS.468-4, defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests. It is currently maintained by the International Telecommunication Union who took it over from the CCIR.
The loudness war is a trend of increasing audio levels in recorded music, which reduces audio fidelity and—according to many critics—listener enjoyment. Increasing loudness was first reported as early as the 1940s, with respect to mastering practices for 7-inch singles. The maximum peak level of analog recordings such as these is limited by varying specifications of electronic equipment along the chain from source to listener, including vinyl and Compact Cassette players. The issue garnered renewed attention starting in the 1990s with the introduction of digital signal processing capable of producing further loudness increases.
Audio noise measurement is a process carried out to assess the quality of audio equipment, such as the kind used in recording studios, broadcast engineering, and in-home high fidelity.
Loudness monitoring of programme levels is needed in radio and television broadcasting, as well as in audio post production. Traditional methods of measuring signal levels, such as the peak programme meter and VU meter, do not give the subjectively valid measure of loudness that many would argue is needed to optimise the listening experience when changing channels or swapping disks.
The alignment level in an audio signal chain or on an audio recording is a defined anchor point that represents a reasonable or typical level.
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Dialnorm is the metadata parameter that controls playback gain within the Dolby Laboratories Dolby Digital (AC-3) audio compression system. Dialnorm stands for dialog normalization. Dialnorm is an integer value with range 1 to 31 corresponding to a playback gain of -30 to 0 dB (unity) respectively. Higher values afford more headroom and are appropriate for dynamic material such as an action film.
A-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured sound levels in an effort to account for the relative loudness perceived by the human ear, as the ear is less sensitive to low audio frequencies. It is employed by arithmetically adding a table of values, listed by octave or third-octave bands, to the measured sound pressure levels in dB. The resulting octave band measurements are usually added to provide a single A-weighted value describing the sound; the units are written as dB(A). Other weighting sets of values – B, C, D and now Z – are discussed below.
EBU R 128 is a recommendation for loudness normalisation and maximum level of audio signals. It is primarily followed during audio mixing of television and radio programmes and adopted by broadcasters to measure and control programme loudness. It was first issued by the European Broadcasting Union in August 2010 and most recently revised in August 2020.
Linear Acoustic is an American company based in Lancaster, Pennsylvania that develops technology and manufacturers equipment used by television stations, cable television and satellite television services providers, post-production facilities and other content services providers to control, measure, manage and monitor multi-channel digital audio. The company has been especially active in areas related to automated upmixing and downmixing of multichannel broadcast audio, and with issues related to relative loudness of broadcast audio.
References
- ↑ E.M. Grimm; R. van Everdingen; M. J. L. C. Schöpping. Towards a Recommendation for a European Standard of Peak and LKFS Loudness Levels (PDF) (Technical report). Archived from the original (PDF) on 2014-09-12.
- ↑ "Mastering & loudness – FAQ". Spotify for Artists. Archived from the original on 2021-03-02. Retrieved 2020-02-13.
- ↑ "Mixing and Mastering Using LUFS". Mastering The Mix. Retrieved 2020-02-13.
- ↑ ITU-R BS.1770 Algorithms to measure audio programme loudness and true-peak audio level (PDF), International Telecommunication Union (ITU)
- ↑ R 128 LOUDNESS NORMALISATION AND PERMITTED MAXIMUM LEVEL OF AUDIO SIGNALS (PDF), European Broadcasting Union
- ↑ ITU-R BS.1770-2 Algorithms to measure audio programme loudness and true-peak audio level (PDF), International Telecommunication Union
- ↑ ITU-R BS.1770-3 Algorithms to measure audio programme loudness and true-peak audio level (PDF), International Telecommunication Union
- ↑ ITU-R BS.1770-4 Algorithms to measure audio programme loudness and true-peak audio level (PDF), International Telecommunication Union
- ↑ ITU-R BS.1770-5 Algorithms to measure audio programme loudness and true-peak audio level (PDF), International Telecommunication Union
- ↑ EBU Recommendation R 128: Loudness normalisation and permitted maximum level of audio signals (PDF), European Broadcasting Union, August 2011, p. 3, retrieved 2013-05-31
- ↑ EBU Tech 3343 - Practical guidelines for Production and Implementation in accordance with EBU R 128 (PDF), European Broadcasting Union, retrieved 2014-03-14
- ↑ Loudness Explained, TC Electronics, retrieved 2018-02-19