It was suggested by Wright in The Tube Preamp Cookbook ¹ that Neumann cutting lathes incorporated this bandwidth defining filter by means of an extra, high-frequency pole at 3.18µS (50 kHz) in the cutting equaliser.

However, when the RIAA equalization standard was written, it was just assumed that the lathe manufacturer would include some kind of bandwidth limiting filter to define the upper skirt of the passband, which is exactly what they did. And it wouldn't be desirable anyway because an equaliser with such a transfer characteristic would amplify any spurious supersonic signals and noise thereby putting the recording cutter-head amplifier, coils, chisel and lacquer under unnecessary stress. No equaliser can ever provide infinite gain. Where T 1 = 3180µS, T 2 = 318µS, and T 3 = 75µSįrom which it's fairly easy to see that H(jω) ⇒ ∞ as ω ⇒ ∞.

Neumann's disc cutting system with lathe and electronics rack - circa 1968Īs specified in the standard, the transfer function of the RIAA equalisation on the record side is given by, Stereo Lab - RIAA and the Neumann Pole Neumann's Last Pole - Revised in March 2020

Riaa equalization audacity