Hi,
the original RIAA curve is defined by the 3 time constants 3180µs (pole), 318µs (zero) and 75µs (pole). These time constants can be represented by the frequencies 50Hz, 500Hz and 2122Hz. Later a second zero at 7950µs (zero) was added. This is the so called RIAA/IEC variant.
Since this preequalization curve raises till infinite with rising frequencies and since this is non practical with reallife cutterheads the company Neumann introduced a variant with an additional zero at ~3.18µs. The amplitude response of the preequalization curve levels out above 50kHz. This is called the RIAA-Neumann variant, which afaik has never become a official standard.
In playback RIAA and RIAA/IEC differ in that the IEC-variant adds a subsonic-lowpass filter at 20Hz. The Neumann variant differs to the RIAA-standards in that its bandwidth limit raises from app. 20kHz to higher values.
For a sufficient description of the curve a reference point in frequency and level is needed. Usually 1kHz and anormalized-to-0dB-level is taken. But it could as well be taken from 20Hz or 20kHz or whereever You want and at any reference level you want.
jauu
Calvin
ps. sreten, could You explain what you mean? To me it doesn´t make sense