On 12/10/12 7:44 PM, robert bristow-johnson wrote:> On 12/10/12 5:57 PM, dvsarwate wrote: >> >> All BPFs and HPFs have (negligibly) small >> DC responses, just as all real LPFs have >> (negligibly) small responses at high >> frequencies. > > i don't think that's true, Dilip. want some counter-examples? (i'll bet > you can figure out some counter-examples.) >i just realized that i didn't quote what i should've:> More practically, > H(f) will be **very small**, but not identically > 0 (or within round-off error if numerical > integration is being done), for a BPF or HPF.Dilip, i think you can *practically* design a filter, either FIR or IIR, with a zero smack dab on (or "spot on" if you're UK) DC or where z=1. i don't think there is any numerical issue stopping you from doing that. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
filter impuse response
Started by ●December 9, 2012
Reply by ●December 11, 20122012-12-11
Reply by ●December 11, 20122012-12-11
"manishp" <58525@dsprelated> writes:> Sirs, > > I would like to know if obsevration of impulse response of a filter gives > some clue the type of filter it is (low pass, high pass). > > For example, I am seeing impulse response of a filer which is a LPF. The > impulse response is just a damping sinusoidal waveform. > > Thanks,Why is it important? Just look at it in the frequency domain (transform the impulse response) and you'll know instantly. -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
Reply by ●December 11, 20122012-12-11
On Mon, 10 Dec 2012 17:36:44 -0500, robert bristow-johnson <rbj@audioimagination.com> wrote:>On 12/10/12 11:52 AM, Greg Berchin wrote: >> What was I thinking? If the integral of the impulse response is zero, then the filter has a general highpass (or possibly bandpass) response. > >what i was thinking (and my whole answer is essentially a guess from my >own experience) is that an HPF will be an LPF modulated up to Nyquist. >that's why i would expect most (not all) samples to have the opposite >sign that their adjacent neighbors have.True for discrete time systems (notwithstanding the noteworthy counterexample already presented), but there is also the continuous time case to be considered.
