relation btw. Delay of a filter & its Order?

Hi

can anybody explain to me what is the relation between the time delay produced by a filter (e.g. a 10th order butterworth filter) and its order?

What is meant by the delay? is it the maximum delay or the delay at the cut-off frequency?

waiting for response ....


best regards

Hello amihomo, I think that the delay is related to the cut-off delay frecuency.-

Hello,

When a signal is being filtered, it will have a frequency response both in magnitude and phase. The delay in filtering is associated with phase response. Which literraly means your output of the filtered signal will be delayed by a magnitude measurable with phase response.

Hope this helps..

amihomo said:

Hi

can anybody explain to me what is the relation between the time delay produced by a filter (e.g. a 10th order butterworth filter) and its order?

What is meant by the delay? is it the maximum delay or the delay at the cut-off frequency?

waiting for response ....


best regards

Click to expand...

You could plot the delay-to-frequency response with matlab function groupdelay. IIR has nonlinear phase delay, which limits its usage. If possible, please use FIR.

noviceca said:

You could plot the delay-to-frequency response with matlab function groupdelay. IIR has nonlinear phase delay, which limits its usage. If possible, please use FIR.

Click to expand...

hi dear noviceca
thank you for your reply.
but , i'm still not clear about what is meant by the DELAY ,is it the group gelay at the cut-off frequency

for example, when we say a filter has a delay of 10 sampling periods, do we address the group delay?

best regards

Hi,

The group delay depends on the phase response of your filter and is frequency dependent. It is in fact the derivative of your filter's phase with respect with frequency. If your signal contains different frequencies, then these frequencies could take different amount of time to pass through your filter, if your group delay is not constant. That would lead to distorsion....
Hope this helps.

RFCMOS

thank you guys for your comments

as we know, there are two types of delay : carrier and envelope delay (also known as group delay).

but in practice , when we use the term DELAY , do we mean the rise time of the step response of the filter?

regards

delay is half the filter length appoximatly

nagacnu said:

delay is half the filter length appoximatly

Click to expand...

hi
how do you justify your claim?

please explain

regards

guess you can talk about 2 types of delay. In analog sense, delay for an analog filter is defined in the way already nicely explained by RFCMOS. I think it means that if you were it give a frequency sweep to an constant delay filter (frequency being always within the constant group delay range of the filter), the output would be frequency-wise exactly the same as the input (ie ignore magnitude).

You can also talk about the delay of a filter, if it is digital, in terms of number of samples. Perhaps you can simply express above "analog" delay in terms of sampling periods for a paritcular frequency or frequency range, like pass band (if it is constant in this range). Like...if there is a zero crossing in a sinewave's samples given at the input of a digital filter how many samples later would you see the zero crossing for that sinewave at the ouput of a digital filter? This is the delay of that filter in sampling period terms for that particular frequency. Agree?

In addition, AFAIK there are is no reason to analyse filter in any different way becuase the input signal happens to be modulated and has some envelope and carrier content. It is completely defined by the phase and frequncy reponse plots.
-b