Rumble (noise)
Encyclopedia
A rumble is a form of low-frequency noise
created by a random sound wave existing between certain limitation points. In audio
rumble refers to a low frequency sound from the bearings inside a turntable
. This is most noticeable in low quality turntables with ball bearings. Higher quality turntables use slide bearings, minimizing rumble.
Some phono pre-amplifiers implement a rumble filter, in an attempt to remove the noise. A heavier platter can also help dampen 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 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 of 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.
, 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.
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.
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
created by a random sound wave existing between certain limitation points. In audio
Sound recording and reproduction
Sound recording and reproduction is an electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording...
rumble refers to a low frequency sound from the bearings inside a turntable
Turntable
A turntable is generally a rotating platform, and may refer to:-Music:* Turntable, a motor-driven platform that normally rotates a gramophone record at a constant rotational velocity as part of a phonograph....
. This is most noticeable in low quality turntables with ball bearings. Higher quality turntables use slide bearings, minimizing rumble.
Some phono pre-amplifiers implement a rumble filter, in an attempt to remove the noise. A heavier platter can also help dampen this.
Rumble measurement is carried out on turntables (for vinyl recordings) which tend to generate very low frequency noise originating from the centre bearing
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
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
Intermodulation
Intermodulation or intermodulation distortion is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities...
, modulating of 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 filterLow-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut 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
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
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
Damping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
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 filterHigh-pass filter
A high-pass filter is a device that passes high frequencies and attenuates frequencies lower than its cutoff frequency. A high-pass filter is usually modeled as a linear time-invariant system...
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 measurementAudio quality measurementAudio 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....
- Noise measurementNoise measurementNoise 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....
- Headroom
- Wow & flutter measurement
- Crosstalk measurementCrosstalk measurementCrosstalk 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 hard to keep below the desired...
- ITU-R 468 noise weightingITU-R 468 noise weightingITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests...
- A-weightingA-weightingA Weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...
- Weighting filterWeighting filterA weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others, for measurement or other purposes.- Audio applications :...
- Equal-loudness contourEqual-loudness contourAn equal-loudness contour is a measure of sound pressure , 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...
- Fletcher-Munson curves