RIAA equalization
Encyclopedia
Gramophone record
A gramophone record, commonly known as a phonograph record , vinyl record , or colloquially, a record, is an analog sound storage medium consisting of a flat disc with an inscribed, modulated spiral groove...
s, established by the Recording Industry Association of America
Recording Industry Association of America
The Recording Industry Association of America is a trade organization that represents the recording industry distributors in the United States...
(RIAA). The purpose of the equalization
Equalization (audio)
Equalization is the process commonly used in sound recording and reproduction to alter the frequency response of an audio system using linear filters. Most hi-fi equipment uses relatively simple filters to make bass and treble adjustments. Graphic and parametric equalizers have much more...
is to permit greater recording times, improve sound quality, and to limit the vinyl damages that would otherwise arise from recording analog records.
The RIAA equalization curve was intended to operate as a de facto
De facto
De facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
global industry standard for the recording and playback of vinyl records since 1954. However, it is almost impossible to say when the change actually took place.
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.
The RIAA curve
RIAA equalization is a form of preemphasisPreemphasis
In processing electronic audio signals, pre-emphasis refers to a system process designed to increase the magnitude of some frequencies with respect to the magnitude of other frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as...
on recording, and deemphasis
Deemphasis
In telecommunication, de-emphasis is the complement of pre-emphasis, in the antinoise system called emphasis. Emphasis is a system process designed to decrease, , the magnitude of some frequencies with respect to the magnitude of other frequencies in order to improve the overall signal-to-noise...
on playback. A record is cut with the low frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
reduced and the high frequencies boosted, and on playback the opposite occurs. 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
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
. 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 fit into a given surface area, yielding longer playback times. This also has the benefit of eliminating physical stresses on the playback stylus
Stylus
A stylus is a writing utensil, or a small tool for some other form of marking or shaping, for example in pottery. The word is also used for a computer accessory . It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styli are heavily curved to be held more easily...
which might otherwise be hard to cope with, or cause unpleasant distortion
Distortion
A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
.
A potential drawback of the system is that rumble from the playback turntable
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...
's drive mechanism is greatly amplified, which means that players have to be carefully designed to avoid this.
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 amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
. Most hi-fi amplifiers have a built-in phono preamplifier with the RIAA characteristic, though it is often omitted in modern designs, due to the gradual obsolescence of vinyl records. A solution in this case is to purchase an outboard preamplifier with the RIAA equalization curve, which adapts a magnetic cartridge
Magnetic cartridge
A magnetic cartridge is a transducer used for the playback of gramophone records on a turntable or phonograph. It converts mechanical vibrational energy from a stylus riding in a spiral record groove into an electrical signal that is subsequently amplified and then converted back to sound by a...
to an unbalanced −10 dB consumer line-level RCA input. 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 editor
Digital audio editor
A digital audio editor is a computer application for audio editing, i.e. manipulating digital audio. Digital audio editors are the main software component of a digital audio workstation.-For use with music:...
s 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. However, this can add an extra step in processing a sample, and may amplify audio quality issues of the sound card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
being used to capture the signal.
Origins of pre-emphasis
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 LaboratoriesBell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
that the recording pattern of the Western Electric
Western Electric
Western Electric Company was an American electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995. It was the scene of a number of technological innovations and also some seminal developments in industrial management...
"rubber line" magnetic disc cutter had a constant velocity characteristic. 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
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, the bass turnover point, in the amplified microphone signal fed to the recording head. 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
Columbia Records
Columbia Records is an American record label, owned by Japan's Sony Music Entertainment, operating under the Columbia Music Group with Aware Records. It was founded in 1888, evolving from an earlier enterprise, the American Graphophone Company — successor to the Volta Graphophone Company...
and Victor Talking Machine Company
Victor Talking Machine Company
The Victor Talking Machine Company was an American corporation, the leading American producer of phonographs and phonograph records and one of the leading phonograph companies in the world at the time. It was headquartered in Camden, New Jersey....
had a higher amplitude in the midrange region. 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.
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.
Standardization
Evidence from the early technical literature concerning electrical recording suggests that it was not until the 1942–1949 period that there were serious efforts to standardize recording characteristics within an industry. Before this time, 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 CorporationBrunswick Corporation
The Brunswick Corporation , formerly known as the Brunswick-Balke-Collender Company, is a United States-based corporation that has been involved in manufacturing a wide variety of products since 1845. Brunswick's global headquarters is in the northern Chicago suburb of Lake Forest, Illinois...
) did was different from the practices of Victor.
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
National Association of Broadcasters
The National Association of Broadcasters is a trade association, workers union, and lobby group representing the interests of for-profit, over-the-air radio and television broadcasters in the United States...
(NAB), later known as the National Association of Radio and Television Broadcasters (NARTB). 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
Cellulose acetate
Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...
, lacquer
Lacquer
In a general sense, lacquer is a somewhat imprecise term for 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 sheen level from ultra matte to high gloss and that can be further polished as required...
/aluminum, and vinyl disc media. 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 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
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
) radio broadcasting. 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.
It is generally thought that 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. However, as most scholars now agreed that it would be impossible to achieve a global standard overnight, it is almost impossible to say when the change actually took place.[1]
It is suspected that many records were still using EQ curves other than the RIAA well into the 70s. As a result, recently more and more high-end audio manufacturers have been bringing out Phono Equalizers with selectable EQ curves:
Abingdon Music Research (AMR) PH-77
Audio Research (AR) Reference Phono 2
Boulder 2008
EMT JPA-66
FM Acoustics 223
Graham Slee JAZZ CLUB
Millenium Media LOC, LPE-2
Monk Audio Phono Preamplifier
VADLYD MD12
YS Audio Concerto
Zanden 1200mk3
Often the following additional stereo EQ curves are included:
Columbia
Decca
CCIR
TELDEC (Direct Metal Mastering
Direct Metal Mastering
Direct Metal Mastering is a vinyl record manufacturing technology by TELDEC. Records manufactured with this technology are often marked by a "DMM" logo on the outer record sleeve....
)
The Enhanced RIAA curve
The official RIAA standard sets three time-constants. The third time-constant requires the cutting lathe to keep boosting high frequencies up to infinity. This is clearly quite impossible. The RIAA standard did not define any LF or HF roll-off for either cutting or replay. This was understandable in the light of the bandwidth restrictions common in 1950's electronics when the RIAA EQ standard was set.Real cutting systems and real playback systems have both low-frequency and high-frequency roll-offs. An essential feature of all cutting lathes, including the Neumann cutting lathes, is a High-Frequency roll-off above 20KHz; effectively a 4th time constant that is not standardised anywhere, but set by the maker of the cutting lathe and electronics.
The so-called ‘Enhanced RIAA’ curve or ‘eRIAA’ curve attempts to address the inherent roll-off by ‘mirroring’ the natural roll-off with an opposing boost from the cutting lathe to ‘add back’ the high frequencies lost, adding a further time-constant during playback.
Background
The official RIAA standard sets three time-constants. The IEC defined in 1972 a fourth time-constant for the playback LF roll-off as 7950uS/20Hz in the IEC98 Standard.This so-called IEC amendment to the RIAA curve is not universally seen as desirable. It has been and remains subject to debate some 35 years later without any formal conclusion.
Some manufacturers follow the IEC standard, others do not while the remainder make this IEC-RIAA user-selectable.
Since the 1980's and onwards a number of sources
have advocated another time constant to define the behaviour of the playback system at high frequencies. An additional HF time-constant was for example, illustrated in the seminal 1980 work on RIAA Playback Equalisation by Lipshitz/Jung, though it was noted as unwanted.
According to some sources the standard HF roll-off designed into the cutting amplifiers used in Neumann lathes is set at 3.18uS/50KHz, effectively forming another additional time constant to those originally defined by the RIAA. As with the IEC Amendment, these suggestions have remained controversial and are subject to ongoing debate. Some manufacturers implement this additional standard, others do not and still others have made both options user-selectable.
It is worth noting that many common phono preamplifier designs utilise negative feedback equalisation. These include an "unwanted" HF time constant at high frequencies similar to that proposed by Wright et al due to the fact that these preamplifiers have a minimum gain of unity. For many common circuits of Phonostages with around 30dB of Gain this HF time constant falls depended on the precise circuit used around 60KHz. Some phono preamplifiers include additional circuitry to correct this and ensure that the output follows the RIAA curve accurately, however in most, they are omitted.
By comparison many "audiophile" phono stages use circuits that correctly follow the nominal RIAA Curve to the letter without an additional high-frequency time constant.
Some manufacturers implement the 3.18uS time-constant either intentionally or as a consequence of the chosen circuit topology, others do not and still others make it a user-selectable feature.
IEC RIAA curve
An improved version of the replay curve (but not the recording curve) was proposed to the International Electrotechnical CommissionInternational Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
with an extra high-pass filter at 20 Hz (7950 µs). The justification was that DC coupling was becoming more common, which meant that turntable rumble would become a greater problem. However, the proposal did not achieve traction, as manufacturers considered that turntables, arm and cartridge combinations should be of sufficient quality for the problem not to arise.
TELDEC/DIN Curve
Telefunken and Decca founded a record company (Teldec) that used a characteristic proposed for German DIN-Standard on July 1957: DIN45533, DIN45536, DIN45537. It is similar, though not equal, to RIAA. The extent of usage of this curve is unclear.Time Constants: 3180 µs (50 Hz), 318 µs (500 Hz), and 50 µs (3,180 Hz).
Compare to RIAA time constants 3180 µs (50 Hz), 318 µs (500 Hz), and 75 µs (2,120 Hz).