RIAA equalization is a specification for the correct playback of gramophone records, established by the Recording Industry Association of America (RIAA). A gramophone The purpose of the equalization is to permit greater playback times, improve sound quality, and to limit the physical extremes that would otherwise arise from recording analog records without such equalization. Equalization (or equalisation, EQ) is the process of changing the frequency envelope of a sound in Audio processing.
The RIAA equalization curve has operated as a de facto global industry standard for the recording and playback of vinyl records since 1954. A technical standard is an established norm or requirement It is usually a formal document that establishes uniform engineering or technical criteria methods processes and practices Before then, especially from 1940, each record company applied its own equalization; there were over 100 combinations of turnover and rolloff frequencies in use, the main ones being Columbia-78, Decca-U. S. , European (various), Victor-78 (various), Associated, BBC, NAB, Orthacoustic, World, Columbia LP, FFRR-78 and microgroove, and AES.
Equalization practice for electrical recordings dates to the beginning of the art. In 1926 it was disclosed by Joseph P. Maxwell and Henry C. Harrison from Bell Telephone Laboratories that the recording pattern of the Western Electric "rubber line" magnetic disc cutter had a constant velocity characteristic. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Western Electric Company (sometimes abbreviated WE and WECo) was an American Electrical engineering company the manufacturing arm This meant that as frequency increased in the treble, recording amplitude decreased. Conversely, in the bass as frequency decreased, recording amplitude increased. Therefore, it was necessary to attenuate the bass frequencies below about 250 Hz, the bass turnover point, in the amplified microphone signal fed to the recording head. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Otherwise, bass modulation became excessive and overcutting took place into the next record groove. When played back electrically with a magnetic pickup having a smooth response in the bass region, a complementary boost in amplitude at the bass turnover point was necessary. G. H. Miller in 1934 reported that when complementary boost at the turnover point was used in radio broadcasts of records, the reproduction was more realistic and many of the musical instruments stood out in their true form.
West in 1930 and later P. G. H. Voight (1940) showed that the early Wente-style condenser microphones contributed to a 4 to 6 dB midrange brilliance or pre-emphasis in the recording chain. This meant that the electrical recording characteristics of Western Electric licensees such as Columbia Records and Victor Talking Machine Company had a higher amplitude in the midrange region. Columbia Records is an American Record label founded in 1888 Columbia is the oldest surviving Brand name in pre-recorded sound being the first record company Victrola redirects here For other uses see Victrola (disambiguation The Victor Talking Machine Company ( 1901 – 1929 Brilliance such as this compensated for dullness in many early magnetic pickups having drooping midrange and treble response. As a result, this practice was the empirical beginning of using pre-emphasis above 1,000 Hz in 78 and 33 1/3 rpm records, some 29 years before the RIAA curve. In processing electronic audio signals preemphasis refers to a system process designed to increase within a band of frequencies the magnitude of some (usually higher frequencies
Over the years a variety of record equalization practices emerged and there was no industry standard. For example, in Europe,for many years recordings required playback with a bass turnover setting of 250 to 300 Hz and a treble rolloff at 10,000 Hz ranging from 0 to -5 dB, or more. In the United States there were more varied practices and a tendency to use higher bass turnover frequencies, such as 500 Hz, as well as a greater treble rolloff like -8. 5 dB, and more. The purpose was to record higher modulation levels on the record.
Evidence from the early technical literature concerning electrical recording suggests that it wasn't until the 1942-1949 period that there were serious efforts to standardize recording characteristics within an industry. Heretofore, electrical recording technology from company to company was considered a proprietary art all the way back to the 1925 Western Electric licensed method first used by Columbia and Victor. For example, what Brunswick-Balke-Collender (Brunswick Corporation) did was different from the practices of Victor. The Brunswick Corporation, formerly known as the Brunswick-Balke-Collender Company, is a United States -based Corporation that has been involved in
Broadcasters were faced with having to adapt daily to the varied recording characteristics of many sources: various makers of "home recordings" readily available to the public, European recordings, lateral cut transcriptions, and vertical cut transcriptions. Efforts were started in 1942 to standardize within the National Association of Broadcasters (NAB), later known as the National Association of Radio and Television Broadcasters (NARTB). National Association of Broadcasters (NAB is a trade association representing the interests of for-profit over-the-air radio and television broadcasters in the United States The NAB, among other items, issued recording standards in 1949 for laterally and vertically cut records, principally transcriptions. A number of 78 rpm record producers as well as early LP makers also cut their records to the NAB/NARTB lateral standard.
The lateral cut NAB curve was remarkably similar to the NBC Orthacoustic curve which evolved from practices within the National Broadcasting Company since the mid-1930s. Empirically, and not by any formula, it was learned that the bass end of the audio spectrum below 100 Hz could be boosted somewhat to override system hum and turntable rumble noises. Likewise at the treble end beginning at 1,000 Hz, if audio frequencies were boosted by 16 dB at 10,000 Hz the delicate sibilant sounds of speech and high overtones of musical instruments could survive the noise level of cellulose acetate, lacquer/aluminum, and vinyl disc media. Cellulose acetate, first prepared in 1865 is the Acetate Ester of Cellulose. In a general sense lacquer is a clear or coloured Varnish, that dries by solvent evaporation and often a curing process as well that produces a hard durable finish in any When the record was played back using a complementary inverse curve (de-emphasis), signal to noise ratio was improved and the programming sounded more lifelike. In telecommunication deemphasis is a system process designed to decrease within a band of frequencies the magnitude of some (usually higher frequencies with respect to the magnitude
In a related area, around 1940 treble pre-emphasis similar to that used in the NBC Orthacoustic recording curve was first employed by Edwin Howard Armstrong in his system of Frequency Modulation (FM) radio broadcasting. Edwin Howard Armstrong ( December 18, 1890 &ndash January 31, 1954) was an American Electrical engineer and Inventor FM radio receivers using Armstrong circuits and treble de-emphasis would render high quality wide-range audio output with low noise levels.
When the Columbia LP was released in June 1948, the developers subsequently published technical information about the 33 1/3 rpm, microgroove, long playing record. Columbia disclosed a recording characteristic showing that it was like the NAB curve in the treble, but had more bass boost or pre-emphasis below 150 Hz. The authors disclosed electrical network characteristics for the Columbia LP curve. This was the first such curve based on formulae.
In 1951 at the beginning of the post-World War II high fidelity (hi-fi) popularity, the Audio Engineering Society (AES) developed a standard playback curve. This was intended for use by hi-fi amplifier manufacturers. If records were engineered to sound good on hi-fi amplifiers using the AES curve, this would be a worthy goal towards standardization. This curve was defined by the time constants of audio filters and had a bass turnover of 400 Hz and a 10,000 Hz rolloff of -12 dB.
RCA Victor and Columbia were in a "market war" concerning which recorded format was going to win: the Columbia LP versus the RCA Victor 45 rpm disc (released in February 1949). Besides also being a battle of disc size and record speed, there was a technical difference in the recording characteristics. RCA Victor was using "New Orthophonic" whereas Columbia was using the LP curve.
Ultimately the New Orthophonic curve was disclosed in a publication by R. C. Moyer of RCA Victor in 1953. He traced RCA Victor characteristics back to the Western Electric "rubber line" recorder in 1925 up to the early 1950s laying claim to long-held recording practices and reasons for major changes in the intervening years. The RCA Victor New Orthophonic curve was within the tolerances for the NAB/NARTB, Columbia LP, and AES curves. It eventually became the technical predecessor to the RIAA curve and superseded all other curves. By the time of the stereo LP in 1958, the RIAA curve, identical to the RCA Victor New Orthophonic curve, became standard throughout the national and international record markets.
RIAA equalization is therefore a form of preemphasis on recording, and deemphasis on playback. In processing electronic audio signals preemphasis refers to a system process designed to increase within a band of frequencies the magnitude of some (usually higher frequencies In telecommunication deemphasis is a system process designed to decrease within a band of frequencies the magnitude of some (usually higher frequencies with respect to the magnitude A record is cut with the low frequencies reduced and the high frequencies boosted, and on playback the opposite occurs. Frequency is a measure of the number of occurrences of a repeating event per unit Time. The result is a flat frequency response, but with noise such as hiss and clicks arising from the surface of the medium itself much attenuated. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium The other main benefit of the system is that low frequencies, which would otherwise cause the cutter to make large excursions when cutting a groove, are much reduced, so grooves are smaller and more can be fitted in a given surface area, yielding longer playback times. This also has the benefit of eliminating physical stresses on the playback stylus which might otherwise be hard to cope with, or cause unpleasant distortion. A stylus (plural styli or styluses) is a Writing utensil. The word is also used for a computer accessory ( PDAs) A distortion is the alteration of the original shape (or other characteristic of an object image sound waveform or other form of information or representation
A potential drawback of the system is that rumble from the playback turntable's drive mechanism is greatly amplified, which means that players have to be carefully designed to avoid this. Rumble measurement is carried out on turntables (for vinyl recordings which tend to generate very low frequency noise originating from the centre Bearing and from The phonograph, or gramophone, was the most common device for playing recorded Sound from the 1870s through the 1980s
RIAA equalization is not a simple low-pass filter. It carefully defines transition points in three places - 75 µs, 318 µs and 3180 µs, which correspond to 2122 Hz, 500 Hz and 50 Hz. Implementing this characteristic is not especially difficult, but more involved than a simple linear amplifier. The word linear comes from the Latin word linearis, which means created by lines. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. The phono input of most hi-fi amplifiers have this characteristic built in, though it is omitted in many modern designs, due to the gradual obsolescence of vinyl records. High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction A solution in this case is to buy a special preamplifier which will adapt a magnetic cartridge to a standard line-level input, and implement the RIAA equalization curve separately. A magnetic cartridge is a Transducer used for the playback of Gramophone records on a turntable or phonograph. Line level is a term used to denote the strength of an audio signal used to transmit analog sound information between audio components such as CD and DVD Some modern turntables feature built-in preamplification to the RIAA standard. Special preamplifiers are also available for the various equalization curves used on pre-1954 records.
Digital audio editors often feature the ability to equalize audio samples using standard and custom equalization curves, removing the need for a dedicated hardware preamplifier when capturing audio with a computer. A digital audio editor is a computer application for Audio editing, i However, this can add an extra step in processing a sample, and may amplify audio quality issues of the sound card being used to capture the signal. A sound card (also known as an audio card is a Computer Expansion card that facilitates the input and output of audio signals to/from a computer under
References
- Powell, James R. , Jr. The Audiophile's Technical Guide to 78 RPM, Transcription, and Microgroove Recordings. 1992; Gramophone Adventures, Portage, MI. ISBN 0-9634921-2-8
- Powell, James R. , Jr. Broadcast Transcription Discs. 2001; Gramophone Adventures, Portage, MI. ISBN 0-9634921-4-4
- Powell, James R. , Jr. and Randall G. Stehle. Playback Equalizer Settings for 78 RPM Recordings. Second Edition. 1993, 2001; Gramophone Adventures, Portage, MI. ISBN 0-9634921-3-6
External links
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic