Trying to test Filter using NCO Megafunction and Signal Tap Analyzer?

Sampling rate of your signal is inherent in that signal you are given for example it could be 27Msps then you are free to choose your system clock. The easiest way is to use a clock = 27MHz then you process each sample per clock.

You may opt to use 54Mhz clock in which case you can process two channels(if you have two of them) of 27Msps; one channel per clock period sharing same one resource.

Additionally if you have one channel then you may process at double speed for resource sharing e.g. compute half of filter sum of products in one cycle and second half in second clock then add up both halves so you may use half multipliers.

If your clock is 13.5MHz then you need to double resource to process one channel into two subchannels (even/odd).

Normally if you have one data channel then there is no need to make your system clock any different from sampling rate unless you are short of resource.