Talk:Finite impulse response

It looks like the two zeros shown in the example repeat z1. Should there be a z2 as I have added? I am not sure of the signs, either. Also, should there be an i in there?

Thanks - Paul Wilfong paul.wilfong at ngc.com

Thanks for pointing out the typo. Engineers use $j$ isntead of $i$ because the later one could be confused with the current...Faust o 21:30, 4 March 2006 (UTC)[reply]

In the article's example, I plead ignorance about how to read the frequency response plot. It looks to me like the filter is fully passing frequencies at 2pi.

That is something for a further discussion. The spectrum of a discrete time signal, such as the impulse response of an FIR filter, is periodic. In layman's terms, imagine yourself walking along the unit circle in the complex z-domain. The absolute value of the function you experience is the amplitude response. The point (1,0) corresponds to the dc (\omega=0). Clearly your walk will be periodic, i.e. you pass the same points all over again, and so is the frequency response of the filter.Faust o 21:30, 4 March 2006 (UTC)[reply]

Also, how do values of the two zeros, shown to be $-1/2\pm j{\sqrt {3}}/2$ , translate to the z1 and z2 values on the frequency plots, which look to me to be about .75pi and 1.25pi?

I updated the figures, angle(z1)\approx .75pi and angle(z2)\approx 1.25pi. Faust o 21:30, 4 March 2006 (UTC)[reply]

Thanks - Paul Wilfong paul.wilfong at ngc.com

Frequency response relative to sampling frequency

It seems to me that this article is a bit misleading by presenting the frequency response as if they are real frequencies. Are they not relative to the sampling frequency? Pi on the graph corresponds to 1/2 of the sampling frequency, and frequencies above that are aliased. vogeljh@juno.com

Stability of FIR filters

In the Properties subsection it is stated that FIR filters "Are inherently stable. This is due to the fact that all the poles are located at the origin and zeros are located within the unit circle."

It is true that FIR filters are inherently stable, and that all the poles are located at the origin. However the zeros can be outside the unit circle and not affect stability, the system would just not be minimum phase. --Stefantarrant 17:34, 29 September 2006 (UTC)[reply]

To find the impulse reponse...

What does δ(n)- denote as opposed to δ(n)?