It is known, that non-uniformity of the frequency response of the channel influences level of ISI. And what kind of distortions is characteristic for non-uniform group delay time?
group delay time?
Started by ●February 5, 2009
Reply by ●February 5, 20092009-02-05
On Feb 5, 3:08�am, "alex65111" <alex65...@list.ru> wrote:> It is known, that non-uniformity of the frequency response of the channel > influences level of ISI. And what kind of distortions is characteristic for > non-uniform group delay time?A non-constant group delay vs frequency (non-linear phase vs frequency) distorts the pulse shape. This causes ISI. John
Reply by ●February 5, 20092009-02-05
>On Feb 5, 3:08=A0am, "alex65111" <alex65...@list.ru> wrote: >> It is known, that non-uniformity of the frequency response of thechannel>> influences level of ISI. And what kind of distortions is characteristicf=>or >> non-uniform group delay time? > >A non-constant group delay vs frequency (non-linear phase vs >frequency) distorts the pulse shape. This causes ISI. > >John >As on level of pulsations group delay it is possible to estimate effective duration of the impulse response?
Reply by ●February 5, 20092009-02-05
On Feb 5, 3:47�pm, "alex65111" <alex65...@list.ru> wrote:> >On Feb 5, 3:08=A0am, "alex65111" <alex65...@list.ru> wrote: > >> It is known, that non-uniformity of the frequency response of the > channel > >> influences level of ISI. And what kind of distortions is characteristic > f= > >or > >> non-uniform group delay time? > > >A non-constant group delay vs frequency (non-linear phase vs > >frequency) distorts the pulse shape. This causes ISI. > > >John > > As on level of pulsations group delay it is possible to estimate effective > duration of the impulse response?If you have a model for your channel, then it's trivial to find its impulse response. Look at it and determine how much of it has a significantly-large magnitude. Jason
Reply by ●February 5, 20092009-02-05
On 5 Feb, 21:47, "alex65111" <alex65...@list.ru> wrote:> As on level of pulsations group delay it is possible to estimate effective > duration of the impulse response?I can't see that there is a relation between group delay and the duration of the impulse response. For IIR filters the group delay can be finite for all frequencies [*]. Yet the duration of the impulse response is infinitely long. Rune [*] I'm pretty sure that's the case for 1st order Butterworth filters.
Reply by ●February 5, 20092009-02-05
Rune Allnor wrote:> On 5 Feb, 21:47, "alex65111" <alex65...@list.ru> wrote: > >> As on level of pulsations group delay it is possible to estimate effective >> duration of the impulse response? > > I can't see that there is a relation between group delay > and the duration of the impulse response. For IIR filters > the group delay can be finite for all frequencies [*]. > Yet the duration of the impulse response is infinitely long. > > Rune > > [*] I'm pretty sure that's the case for 1st order Butterworth > filters.C'mon, Rune. What's the difference between a first-order Butterworth and a first-order IIR od any class? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 5, 20092009-02-05
On Feb 5, 4:53�pm, Rune Allnor <all...@tele.ntnu.no> wrote:> On 5 Feb, 21:47, "alex65111" <alex65...@list.ru> wrote: > > > As on level of pulsations group delay it is possible to estimate effective > > duration of the impulse response? > > I can't see that there is a relation between group delay > and the duration of the impulse response.well, i think they are linearly related, for a filter of fixed shape and adjustable resonant frequency, f0. lower that frequency and the effective impulse response length (however "effective" is defined) and the mean group delay (however "mean" is defined) both go up in a 1/f0 manner.> For IIR filters > the group delay can be finite for all frequencies [*]. > Yet the duration of the impulse response is infinitely long.how about the "effective duration"? i thought that someone had a result that related integral{ tau(w) * |H(w)|^2 dw} to sum{ n * |h[n]|^2 } for a general filter. i dunno. r b-j r b-j
Reply by ●February 6, 20092009-02-06
On 6 Feb, 00:12, Jerry Avins <j...@ieee.org> wrote:> Rune Allnor wrote: > > On 5 Feb, 21:47, "alex65111" <alex65...@list.ru> wrote: > > >> As on level of pulsations group delay it is possible to estimate effective > >> duration of the impulse response? > > > I can't see that there is a relation between group delay > > and the duration of the impulse response. For IIR filters > > the group delay can be finite for all frequencies [*]. > > Yet the duration of the impulse response is infinitely long. > > > Rune > > > [*] I'm pretty sure that's the case for 1st order Butterworth > > � � filters. > > C'mon, Rune. What's the difference between a first-order Butterworth and > a first-order IIR od any class?Excluding the order, elliptic filters have stuff going on so that the unwrapped phase responses have near-infinite slopes. Rune
Reply by ●February 6, 20092009-02-06
On 6 Feb, 01:39, robert bristow-johnson <r...@audioimagination.com> wrote:> On Feb 5, 4:53�pm, Rune Allnor <all...@tele.ntnu.no> wrote: > > > On 5 Feb, 21:47, "alex65111" <alex65...@list.ru> wrote: > > > > As on level of pulsations group delay it is possible to estimate effective > > > duration of the impulse response? > > > I can't see that there is a relation between group delay > > and the duration of the impulse response. > > well, i think they are linearly related, for a filter of fixed shape > and adjustable resonant frequency, f0. �lower that frequency and the > effective impulse response length (however "effective" is defined) and > the mean group delay (however "mean" is defined) both go up in a 1/f0 > manner. > > > For IIR filters > > the group delay can be finite for all frequencies [*]. > > Yet the duration of the impulse response is infinitely long. > > how about the "effective duration"? > > i thought that someone had a result that related > > � �integral{ tau(w) * |H(w)|^2 dw} > > to > > � �sum{ n * |h[n]|^2 } > > for a general filter. > > i dunno.I haven't seen too many discussions of the group delay, so you might be right. My interpretation is that the group delay says something about the time it takes for a response to occur on the output of the filter, not how long the response lasts. If you want to look at durations of the IR, the locations of the poles are better indicators: The IR of resonant systems last for long times, and these systems have poles close to the unit circle. Rune
Reply by ●February 6, 20092009-02-06
