The decibel is a relative unit of measurement corresponding to one tenth of bel. It is used to express the ratio of one value of a power or field quantity to another, on a logarithmic scale, the logarithmic quantity being called the power level or field level, respectively, it can be used to express a change in an absolute value. In the latter case, it expresses the ratio of a value to a fixed reference value. For example, if the reference value is 1 volt the suffix is "V", if the reference value is one milliwatt the suffix is "m". Two different scales are used when expressing a ratio in decibels, depending on the nature of the quantities: power and field; when expressing a power ratio, the number of decibels is ten times its logarithm to base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level; when expressing field quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two so that the related power and field levels change by the same number of decibels with linear loads.
The definition of the decibel is based on the measurement of power in telephony of the early 20th century in the Bell System in the United States. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell. Today, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics and control theory. In electronics, the gains of amplifiers, attenuation of signals, signal-to-noise ratios are expressed in decibels. In the International System of Quantities, the decibel is defined as a unit of measurement for quantities of type level or level difference, which are defined as the logarithm of the ratio of power- or field-type quantities; the decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. The unit for loss was Miles of Standard Cable. 1 MSC corresponded to the loss of power over a 1 mile length of standard telephone cable at a frequency of 5000 radians per second, matched the smallest attenuation detectable to the average listener.
The standard telephone cable implied was "a cable having uniformly distributed resistance of 88 Ohms per loop-mile and uniformly distributed shunt capacitance of 0.054 microfarads per mile". In 1924, Bell Telephone Laboratories received favorable response to a new unit definition among members of the International Advisory Committee on Long Distance Telephony in Europe and replaced the MSC with the Transmission Unit. 1 TU was defined such that the number of TUs was ten times the base-10 logarithm of the ratio of measured power to a reference power. The definition was conveniently chosen such that 1 TU approximated 1 MSC. In 1928, the Bell system renamed the TU into the decibel, being one tenth of a newly defined unit for the base-10 logarithm of the power ratio, it was named the bel, in honor of the telecommunications pioneer Alexander Graham Bell. The bel is used, as the decibel was the proposed working unit; the naming and early definition of the decibel is described in the NBS Standard's Yearbook of 1931: Since the earliest days of the telephone, the need for a unit in which to measure the transmission efficiency of telephone facilities has been recognized.
The introduction of cable in 1896 afforded a stable basis for a convenient unit and the "mile of standard" cable came into general use shortly thereafter. This unit was employed up to 1923 when a new unit was adopted as being more suitable for modern telephone work; the new transmission unit is used among the foreign telephone organizations and it was termed the "decibel" at the suggestion of the International Advisory Committee on Long Distance Telephony. The decibel may be defined by the statement that two amounts of power differ by 1 decibel when they are in the ratio of 100.1 and any two amounts of power differ by N decibels when they are in the ratio of 10N. The number of transmission units expressing the ratio of any two powers is therefore ten times the common logarithm of that ratio; this method of designating the gain or loss of power in telephone circuits permits direct addition or subtraction of the units expressing the efficiency of different parts of the circuit... In 1954, J. W. Horton argued that the use of the decibel as a unit for quantities other than transmission loss led to confusion, suggested the name'logit' for "standard magnitudes which combine by addition".
In April 2003, the International Committee for Weights and Measures considered a recommendation for the inclusion of the decibel in the International System of Units, but decided against the proposal. However, the decibel is recognized by other international bodies such as the International Electrotechnical Commission and International Organization for Standardization; the IEC permits the use of the decibel with field quantities as well as power and this recommendation is followed by many national standards bodies, such as NIST, which justifies the use of the decibel for voltage ratios. The term field quantity is deprecated by ISO 80000-1. In spite of their widespread use, suffixes are not recognized by the IEC or ISO. ISO 80000-3 describes definitions for units of space and time; the decibel for use in acoustics is defined in ISO 80000-8. The major difference from the article below is t
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Paul Kelly - Stories of Me is a 2012 Australian documentary directed by Ian Darling and produced by Shark Island Productions. The film sold out within 10 hours at the 2012 Melbourne International Film Festival and before its official theatrical release on 25 Oct 2012, the film went on a sold out National Tour as special event releases with Paul Kelly and director Ian Darling appearing on stage after the screening, it was broadcast on the ABC on 27 October 2012. With a career spanning more than thirty years, this feature-length documentary explores Kelly's life from his childhood in Adelaide as the sixth of nine children and grandson of two famous opera singers, through to his reputation as one of Australia's best singer-songwriters; the relationship of Kelly's art to his life and personal journey are revealed as are the many hurdles he faced along the way. The interview subjects include various members of Kelly's family, many of his fellow musicians and friends including novelists Richard Flanagan and Fiona McGregor, film director Rachel Perkins and musicians Megan Washington and Archie Roach.
As part of the film's social impact and educational outreach program Shark Island Productions and The Caledonia Foundation launched Paul Kelly & The Portraits at the National Portrait Gallery by The Hon Tony Burke MP and Paul Kelly - Portrait of an Artist Schools' Education and Curriculum program by The Hon Peter Garrett AM and developed with the English Teachers Association NSW. The report Music to Our Ears with the Music Council of Australia was commissioned to increase parental engagement to advance music education in schools. Paul Kelly - The Essays is a companion paperback book and e-book to the film tracking Kelly's life from aspiring cricketer as a young boy through to his status as one of Australia's best musicians. Paul Kelly - Stories of me Study Guide Music to Our Ears Commissioned Report Paul Kelly - Portrait of an Artist Curriculum Resource Won ATOM AWARD Best Educational/Training Resource Won ATOM AWARD Best Documentary Arts Finalist ATOM AWARD Best Documentary General Finalist ATOM AWARD Best Documentary Biography Won Australian Screen Sound Guild Award Best Sound in a Documentary Won FCCA Award Best Documentary Nominated AACTA Award Best Sound in a Documentary Paul Charlier Nominated ADG Award Best Documentary Feature Ian Darling Won ASE Award Best Documentary Editing Sally Fryer Official Selection at the Melbourne International Film Festival 2012 Official Selection at the Canberra International Film Festival 2012 Cast Paul Kelly Production Ian Darling as Director Sally Fryer ASE as Editor Susan Mackinnon as Producer Mary Macrae as Producer Toby Creswell as Executive Producer David Leser as Executive Producer Simon Smith as Director of Photography Benjamin Cunningham as Cinematographer Paul Charlier as Sound Designer and Music MixerMusic Paul Kelly Official website Paul Kelly - Stories of Me on IMDb