![]() ![]() ![]() The bandwidth of the filter is always specified to the -3dB point, so in the first iteration of design our filter has a smaller bandwidth than specified (somewhere less than 9kHz). We can see from the first figure that the attenuation in the stopband exceeded our specifications, perhaps we can tweak the attenuation and passband frequency to enhance the design. The code above gives us the following response:īut if we zoom in we will see that the attenuation at 10kHz is greater than 3dB: Using the Octave/Matlab code below, we can see how to design a lowpass filter with a bandwidth of 10kHz and a cutoff of 15kHz using Octave's built in fir1 function, which is well documented here close all *Designing an FIR filter length to be odd length will give the filter an integral delay of (N-1)/2. After trying the calculated N, one can then tweak N or parameters which make up N to meet filter specifications. The equation below is an efficient way to compute a reasonable starting length. You can guess and check until the filter matches your expected bandwidth and cutoff requirements, but this could be a long and tedious process. Typically, in FIR filter design the length of the filter will need to be specified. I won't get into the details much further on FIR filters and their pro's and con's as this tutorial focuses more on designing filters fast and efficiently with the aid of Octave. As the series progresses, it will discuss the necessary steps to implement the filter on real hardware.Ī FIR filter is a digital filter whose impulse response settles to zero in finite time as opposed to an infinite impulse response filter (IIR), which uses feedback and may respond indefinitely to an input signal.The great thing about FIR filters is that they are inherently stable and can easily be designed to have linear phase. This tutorial will focus on designing a finite impulse response (FIR) filter. ![]()
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