Questions about DSPBuilder

[Altera_Forum]

I use dspbuilder to design a FIR ,the parameter is input 8bit，output 8bit ,fs 10M ,fc 1M,order16 Direct FIR. 

However the problem is genrated: first,the filter coefficents can not convert to interger;Second,when use the Filter design&analysis tool to convert to interge ,the quantization error is too big to ignore. What can I do ?

[Altera_Forum]

Design a bigger filter?

[Altera_Forum]

You mean that I should increse the filter order,but we kown that the order is still limited in  

improving the performence of the filter.

[Altera_Forum]

I'm not using DSPBuilder and don't know, what "can not convert to integer" means in this regard. I assume, that some kind of coefficient scaling is performed by any FIR design tool. If I use the Quartus FIR compiler, it would also have issues to realize a certain filter characteristics with insufficient coefficient length. You didn't actually tell the used coefficient length or internal data length, just I/O data length of 8 bit.  

 design a bigger filter could be also understood as increasing data and coefficient length, which seems to be necessary in this case. But you have to know your specification, how far 8-bit data length is meaningful for your application and about the intended filter characteristics.