| For those who have limited knowledge of DSP | | | | number of pulses on output of filter ant filter |
| FIR and IIR terms may seem little bit tricky. Well | | | | function generally can be described |
| FIR stands for Finite Impulse Response and IIR | | | | as:y[n]=x[n]*c0+x[n-1]*c1...x[n-N]*cNwhere y[n] is |
| stands for Infinite Impulse Response. Lets see | | | | output signal at instant n, x[n] input signal at |
| what does it mean in popular manner. | | | | instant n, ck - the impulse response from 0 to N |
| All filters have their own characteristics. | | | | instants, N- number of samples in the pulse |
| Characteristic are a response to a pulse applied to | | | | response. |
| filters input. If we know filters response, we can | | | | Lets see what IIR response look |
| easily calculate filters amplitude and phase | | | | *x[n-1]...bk*x[n-k] |
| behaviour. So filter can be imagined as a transfer | | | | We see, that IIR filter is a bit harder to read, |
| function, which gives a certain response to input | | | | because it has a feedback -what means that |
| signal. | | | | output signal y[n] is fed back to input. Naturally |
| In digital systems signal is sampled and each | | | | there is a question, so why use IIR filter if simpler |
| sample is considered as a pulse. Calculation filter | | | | is to use FIR? One of obvious answers are, that |
| response becomes quite easy task. | | | | IIR filter response can be created with few |
| Lets see what filter responses can be. A pulse in | | | | coefficients comparing to FIR. So IIR requires less |
| filters input may cause finite number of output | | | | computing power than FIR. But in other hand FIR |
| pulses, but can cause thousands (theoretically - | | | | filter is easier to design, but gives flat phase |
| infinite number of response pulses). Here we fase | | | | response. FIR filters are also unconditionally stable |
| two therms - FIR and IIR. | | | | while IIR can be unstable if designed poorly. And in |
| IIR as we mentioned is finite impulse response | | | | side effect can oscillation process start. |
| filter, this means that such filter gives finite | | | | |