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Digital Filtering Problem

Question asked by akcay.baycan on Mar 23, 2016
Latest reply on Mar 24, 2016 by akcay.baycan
 I am using STM32f405, and CMSIS dsp library, to filter a signal acquired by ADS1278. The filter used is a 12th order bandpass butterworth IIR filter whose coefficients generated by matlab, and my signal is 2430Hz The problem is;
When I use a filter with a pass band 2300Hz-2500Hz everything work fine. But if a use a more narrow band like 2420Hz-2440Hz filter output is not stable. It is making noise, not periodic but randomly, like 2 seconds ok then a noise, 5 seconds ok then a noise. Matlab says filter is stable for 32bit quantized coefficients, but actually there is problem. 
Can anyone suggest a way to findout where is the problem?