Rumble (noise) - Rumble Filters

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.