Need explanation of basics of the filter parameters

[patan.gova]

Hello,

I observed that the magnitude(dB) value of the respective cutoff frequency is changing when the order for the filter(FIR) is changed.
can someone explain
1) what is the relation between magnitude(dB) to the cutoff frequency of a filter.what should the real of magnitude of cutoff frequency as the theory.
3)why the order of the filter changes the magnitude of the cutoff frequency
3)How the filter response or what will be effected if the order of the filter is changes.
Thanks.

 

[FvM]

There's a detailed online help for Matlab fdesign parameters. E.g. :

Fc — cutoff frequency for the point 6 dB below the passband value. Specified in normalized frequency units.

As far as I know, the design tries to meet the specification. With an unreasonable low tap number (FIR "filter order), it possibly fails the 6 dB point.