Comparison of results with Direct form1 and Direct form2 implementation of IIR filters The results obtained from Direct form1 and Direct form2 implementations (in C language) of IIR (BiQuad) filters are a little different. In the implementation, i have made the b0 coefficient as 1. So, I am just using 4 coefficients (a2,a1,b2,b1) in the implementation. The maximum error between the obtained outputs from these two implementations is in the range of 0.01 for the ITU-T standard audio test signal. So, I just want to know whether this error is because of the implementation, or any other reasons? Will the Outputs of both implementations be the same, always (i.e. error is almost 0)? 

In the implementation, I am using around 8 stages of filtering. (i.e. Cascaded Biquad filters)

The referred structure forms as attached below.
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Will the Outputs of both implementations be the same, always (i.e. error is almost 0)?


That depends A LOT on the numerical precision of your data representation and mathematical operations and on the filter itself, specifically the location of the poles. 

If you use double precision in a communication application, there should be little to no difference. If you are trying to do audio processing with 16-bit fixed point format, the errors induced by Direct Form II are so large that it's basically unusable.