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MakkinTosken
RIAA and Replay RumbleRIAA is the abbreviation for ‘Recording Industry Association of America’ andis the de facto worldwide post-1954 standard for equalisation of microgrooverecords, as opposed to the numerous standards for 78s. Because the RIAAstandard was not invented in Europe, but a worldwide standard was needed, theIEC invented an LP equalisation standard that was almost identical. The onlydifference is that the IEC standard recommends bass cut on replay only, with a−3 dB point at 20 Hz (7,950 μs) in order to reduce rumble. Most manufacturersof high-quality pre-amplifiers assume that their products will be complementedby equally good turntables and that replay rumble will not be a problem, so they
ignore the IEC recommendation. Their equalisation is therefore RIAA.Nevertheless, there is considerable pressure to modify RIAA stages to include alow-frequency roll-off because:• Some valve power amplifiers are susceptible to output transformer coresaturation if high-amplitude signals are applied at low frequencies (<50 Hz).• Bass reflex loudspeakers are easily overloaded at low frequencies becausethere is negligible damping of cone motion below their roll-off frequency.Bookshelf reflex loudspeakers tend to roll off below 100 Hz, whereasfreestanding reflex loudspeakers could improve this to 50 Hz, or less, but thisstill leaves both vulnerable to low frequency noise.• Vinyl records contain low frequency (<20 Hz) noise due to warps andrumble.It is therefore argued that these problems could be avoided by implementingsome form of LF roll-off within the RIAA stage. One possibility is to implementthe IEC 7,950 μs recommendation, but a more sophisticated approach is toincorporate a properly designed high-pass filter having a final slope of 12 dB/octave, or more, set at ≈10 Hz.The author firmly believes that neither of the preceding electrical approaches iscorrect and that RIAA equalisation should be reserved solely for correcting therecord equalisation applied by the manufacturer at the time of cutting. CDplayers do not add a 10 Hz high-pass filter to solve the problems of poorlydesigned loudspeakers or questionable output transformers, so why adulteratevinyl? Warps and rumble are mechanical problems, and should have mechanicalsolutions, not electrical ‘fixes’
