The measuring system is 196kHz, but I have "full range" channels and high pass channels from 2,5kHz cutted both on 15 kHz, so the next harmonics are also attenuated.
btw, the measuring system gents self noise on -130dBu and dynamic range is up to 40 dBu, so I cannot say I am measuring with dBFS. And, for all, previous stages (like the input + attenuator) produces very low noise and little distortion. The two signal followers in attenuator produces wery low noise, but the followers used in Sallen Key filters "do", so the final noise is filtered, but why the noise is produced, dont know... one signal follower can rise the noise about 1 dB or what I know, with noise level at -110 dBu, but this time, it is more than 20 dB worse...