IIR low pass filter: floating point and fixed point I have implemented an IIR low pass filter in direct form 2, the input to the filter is a unit impulse $\delta[n]$. I have calculated the output of the filter for the mentioned input using the difference equation of direct form 2, the equations are given below:

$$\begin{align}w[n] &amp;= x[n] - a_1 w[n-1] - a_2 w[n-2] \\
y[n] &amp;= b_0 w[n] + b_1 w[n-1] + b_2 w[n-2] \end{align}$$


How to plot the frequency response of the output with out using inbuilt commands in MATLAB? Also I want to implement the same in fixed point using 32 bit and plot the frequency reponse of it. 
For plotting should I use freqz command or plot(abs(fft(my ouput))?. Both should give me same frequency response, but I am getting different responses,
setting aside the DF1 vs. DF2 issue (and we know there are several other forms besides those two, all with advantages and disadvantages), there is an answer, sans phase response, to the OP's original question here.