In this Texas app note on current sources, on page 12 it talks about reducing noise by filtering it. But it states:
"Without the capacitor, noise from the current source would
feed directly through to the output. The capacitor filters the
noise at a 3dB frequency of 1/(2 π R C), or about 30Hz
in this example. Filtering below this frequency will not
reduce noise further, since the 30Hz pole is already below
the 1/f corner of the current source, and noise can not be
reduced by filtering in the 1/f region."
http://www.ti.com/lit/an/sboa046/sboa046.pdf
But why would filtering below the 1/f corner not reduce noise further? Surely the more filtering we have, the better things get, whether it is 1/f noise or otherwise?
"Without the capacitor, noise from the current source would
feed directly through to the output. The capacitor filters the
noise at a 3dB frequency of 1/(2 π R C), or about 30Hz
in this example. Filtering below this frequency will not
reduce noise further, since the 30Hz pole is already below
the 1/f corner of the current source, and noise can not be
reduced by filtering in the 1/f region."
http://www.ti.com/lit/an/sboa046/sboa046.pdf
But why would filtering below the 1/f corner not reduce noise further? Surely the more filtering we have, the better things get, whether it is 1/f noise or otherwise?