Rumble measurement

Rumble measurement

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 drive pulleys or belts, as well as from irregularities in the record disc itself.

It can be heard as low-frequency noise, and becomes a serious problem when playing records on audio systems with a good low-frequency response. Even when not audible, rumble can cause intermodulation, modulating the amplitude of other frequencies. The ‘unweighted’ response curve is intended for use in assessing the level of inaudible rumble with such intermodulation in mind.

Turntable design

One way to reduce rumble is to make the turntable very heavy, so that it acts as mechanical damper or low-pass filter, but even with the best turntables a lot of rumble tends to be generated by warped records or pressing irregularities sometimes visible as ‘bobbles’ in the surface. An important factor affecting rumble is low-frequency resonance resulting from pickup arm mass bouncing against stylus compliance. This resonance is usually in the 10–30 Hz region, and will increase rumble as well as reducing tracking ability if not well-damped. Good pickup arms incorporate viscous damping aimed at eliminating such resonance.

Rumble filters

Because these effects generate a mostly vertical component at the stylus, which corresponds to a difference signal in stereo reproduction, the incorporation of a high-pass filter operating only on the channel difference can be very effective in reducing rumble without loss of bass. Such a filter merges the two channels to mono at very low frequencies, which is not generally considered to have any effect on stereo perception, though it can change the sound balance (often for the better) by altering the way in which resonant room modes are stimulated (reducing corner to corner stimulation.. The original circuit was designed in 1978 by Jeff Macaulay and featured as a circuit idea in 'Wireless World' Most so-called rumble filters work by simply rolling off the low-frequency response, which is detrimental to sound quality.

Though several standards exist that define how rumble should be measured, they all have a common basis, and use the weighting curves shown here.DIN 45539 (1971) and IEC98-1964 both cover rumble measurement.BS4852: Part 1 (1972) is specific in requiring that a slow rectifier be used, which shall reach 99% of its steady indication in 5s +-0.5s with not more than 10% overshoot.

See also

*Audio quality measurement
*Noise measurement
*Wow & flutter measurement
*Crosstalk measurement

*ITU-R 468 noise weighting
*Weighting filter
*Equal-loudness contour
*Fletcher-Munson curves

Wikimedia Foundation. 2010.

См. также в других словарях:

  • Rumble — may refer to:People*Darren Rumble, a retired professional ice hockey defensemanMusic* Rumble (song), an instrumental rock song by Link Wray *Rumble Fish (group), a Korean rock band * rumble fish , Do As Infinity s fifth single * Rumble Fish is… …   Wikipedia

  • Audio quality measurement — seeks to quantify the various forms of corruption present in an audio system or device. The results of such measurement are used to maintain standards in broadcasting, to compile specifications, and to compare pieces of equipment. The need for… …   Wikipedia

  • Wow and flutter measurement — is carried out on audio tape machines, cassette recorders and players, and other analog recording and reproduction devices with rotary components (e.g. movie projectors, turntables (vinyl recording), etc.). This measurement quantifies the amount… …   Wikipedia

  • Noise measurement — is carried out in various fields. In acoustics, it can be for the purpose of measuring environmental noise, or part of a test procedure using white noise, or some other specialised form of test signal. In electronics it relates to the sensitivity …   Wikipedia

  • Crosstalk measurement — is made on audio systems to determine the amount of signal leaking across from one channel to another. Interchannel crosstalk applies between the two channels of a stereo system, and is usually not very important on modern systems, though it was… …   Wikipedia

  • Audio noise measurement — is carried out when assessing the quality of audio equipment, such as is used in recording studios, broadcast studios, and in the home (Hi Fi).Noise in general refers to unwanted sound, often loud, but in audio systems it is the low level hiss or …   Wikipedia

  • List of IEC standards — In order to distinguish standards published by the International Electrotechnical Commission numerically from other international standards, their number range was shifted in 1997 by adding 60000. So what used to be called IEC 27 is now… …   Wikipedia

  • A-weighting — A graph of the A , B , C and D weightings across the frequency range 10 Hz – 20 kHz Video illustrating A weighting by analyzing a sine sweep (contains audio) A weighting is the most …   Wikipedia

  • Weighting — The process of weighting involves emphasising some aspects of a phenomenon, or of a set of data giving them more weight in the final effect or result. It is analogous to the practice of adding extra weight to one side of a pair of scales to… …   Wikipedia

  • Headroom — In a digital and analog audio systems, headroom is the amount by which linear signal capabilities exceed actual signal level. In digital audio, headroom is defined as the amount that full scale (FS) exceeds the permitted maximum level (PML) in dB …   Wikipedia

Поделиться ссылкой на выделенное

Прямая ссылка:
Нажмите правой клавишей мыши и выберите «Копировать ссылку»