Anyone who is familiar with vinyl record playback may have heard of the term 'RIAA equalization'. In essence it's an industry wide equalisation spec which enables vinyl records to offer longer playing times and to also improve sound quality and promote record longevity. Using the prescribed equalisation curve during recording, low frequences are reduced and higher frequencies are boosted. And when the record is played back through a pre amplifier, the RIAA curve is electronically inversely re-applied resulting in a mirroring effect, which restores the original sound. In practice the standard RIAA Curve can lead to a low frequency turntable 'rumble' being disproportionately amplified by the RIAA's low frequency boost.
In more recentl times the IEC brought out what has come to be known as the IEC RIAA Curve which is an adaption of the regular RIAA during play back only (not recording) This curve is an attempt to filter subsonic turntable rumble by creating a pole at 20Hz.
Turntable rumble is a low frequency sound which eminates from bearings, belts and drive pulleys inside the turntable. High quality turntables are specifically designed to minimise this by the use of higher quality components.
On the Perreaux Audiant VP3 MM/MC Phono preamplifier it is possible to select the IEC RIAA Curve which will act as an electronic aide to mitigate turntable rumble occuring below 20Hz.
You can select between normal RIAA ans IEC RIAA by selecting dip switch 4 on gain dip switches. Up for IEC RIAA and down for Normal RIAA.