The RIAA curve for a phono preamp has a 40 dB swing from 20 Hz to 20KHz. Half of that is a 20 dB boost of the bass and the other half is a similar cut in the treble. It crosses the zero point at 1 KHz.
However, it is not a completely straight line from boost to cut.
Obviously the more accurate the curve, the closer your LPs' frequency response will be to flat when you play records.
The frequency response will also be influenced by the interaction of the phono cartridge with the preamp. One can have a preamp with a very flat response that becomes a lot less flat if mismatched to a cartridge.
It bears repeating, though, that this one parameter is not the only one that affects a phono preamp's sound quality. Distortion, noise, headroom and other factors are also very important. The ultimate test is what the user thinks of the sound when he plays a record.
However, it is not a completely straight line from boost to cut.
Obviously the more accurate the curve, the closer your LPs' frequency response will be to flat when you play records.
The frequency response will also be influenced by the interaction of the phono cartridge with the preamp. One can have a preamp with a very flat response that becomes a lot less flat if mismatched to a cartridge.
It bears repeating, though, that this one parameter is not the only one that affects a phono preamp's sound quality. Distortion, noise, headroom and other factors are also very important. The ultimate test is what the user thinks of the sound when he plays a record.