Hello, I am curious as to why sampling parameter is important while designing a filter. I guess, it is sufficient that the original signal has been sampled at a sufficient rate. --------------------------------------- Posted through http://www.DSPRelated.com
Filter and sampling rate
Started by ●October 15, 2015
Reply by ●October 15, 20152015-10-15
Sharan123 wrote:> Hello, > > I am curious as to why sampling parameter is important while designing a > filter. I guess, it is sufficient that the original signal has been > sampled at a sufficient rate. > --------------------------------------- > Posted through http://www.DSPRelated.com >When you design analog filters, you deal with time constants. Given a time constant and a periodic signal you get a phase relationship. Given a phase relationship, you get cancellation or reinforcement of the signal at frequency. This is the basic, inherent nature of filters. Digital filters, at least a subset of them, are just an implementation detail. -- Les Cargill
Reply by ●October 15, 20152015-10-15
On Thu, 15 Oct 2015 09:57:37 -0500, Sharan123 wrote:> Hello, > > I am curious as to why sampling parameter is important while designing a > filter. I guess, it is sufficient that the original signal has been > sampled at a sufficient rate.I'm not sure where your confusion lies, but when you design a digital filter all of it's behavior is normalized by the sampling rate. So if you're sampling a real-world signal, when you change the sampling rate then, depending on your point of view, you either change the signal that you're filtering, or you change the characteristics of the filter with respect to real-world frequencies. Feel free to reiterate your question if you need to. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●October 15, 20152015-10-15
>Hello, > >I am curious as to why sampling parameter is important while designing a >filter. I guess, it is sufficient that the original signal has been >sampled at a sufficient rate. >--------------------------------------- >Posted through http://www.DSPRelated.com1) because Fc (and all filter response) is related to Fs 2) implementation can be improved if there is up/dn sampling ratio between input/output of filter. Kaz --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●October 15, 20152015-10-15
On 10/15/15 2:04 PM, Tim Wescott wrote:> On Thu, 15 Oct 2015 09:57:37 -0500, Sharan123 wrote: > >> Hello, >> >> I am curious as to why sampling parameter is important while designing a >> filter. I guess, it is sufficient that the original signal has been >> sampled at a sufficient rate. > > I'm not sure where your confusion lies, but when you design a digital > filter all of it's behavior is normalized by the sampling rate.just to pile on a little more, when computers (or DSPs) crunch numbers, it's only pure numbers they're crunching. they have no idea if the period between adjacent x[n] is a micro-second or a month.> So if > you're sampling a real-world signal, when you change the sampling rate > then, depending on your point of view, you either change the signal that > you're filtering,well you *are* changing the signal (from the computer's POV). e.g. if you're sampling faster, a physical signal remaining at a constant frequency will appear to the computer as lower in frequency.> or you change the characteristics of the filter with > respect to real-world frequencies.which means the filter coefficients have to change if the filter is supposed to treat the new (e.g. lower) frequency the same as it previously treated the older (higher) frequency. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●October 15, 20152015-10-15
Tim Wescott <seemywebsite@myfooter.really> wrote:> On Thu, 15 Oct 2015 09:57:37 -0500, Sharan123 wrote:>> I am curious as to why sampling parameter is important while designing a >> filter. I guess, it is sufficient that the original signal has been >> sampled at a sufficient rate.> I'm not sure where your confusion lies, but when you design a digital > filter all of it's behavior is normalized by the sampling rate.The sampling rate isn't important if your filter frequencies are all relative to the sample rate. It depends on how you do filter design. -- glen
Reply by ●October 16, 20152015-10-16
>On Thu, 15 Oct 2015 09:57:37 -0500, Sharan123 wrote: > >> Hello, >> >> I am curious as to why sampling parameter is important while designinga>> filter. I guess, it is sufficient that the original signal has been >> sampled at a sufficient rate. > >I'm not sure where your confusion lies, but when you design a digital >filter all of it's behavior is normalized by the sampling rate. So if >you're sampling a real-world signal, when you change the sampling rate >then, depending on your point of view, you either change the signal that>you're filtering, or you change the characteristics of the filter with >respect to real-world frequencies. > >Feel free to reiterate your question if you need to.Thanks. I am getting a hang of it. I need to work out a simple filter in Matlab myself and then I will probably have follow-on questions ... --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●October 16, 20152015-10-16
On Fri, 16 Oct 2015 00:53:29 +0000, glen herrmannsfeldt wrote:> Tim Wescott <seemywebsite@myfooter.really> wrote: >> On Thu, 15 Oct 2015 09:57:37 -0500, Sharan123 wrote: > > >>> I am curious as to why sampling parameter is important while designing >>> a filter. I guess, it is sufficient that the original signal has been >>> sampled at a sufficient rate. > >> I'm not sure where your confusion lies, but when you design a digital >> filter all of it's behavior is normalized by the sampling rate. > > The sampling rate isn't important if your filter frequencies are all > relative to the sample rate. > > It depends on how you do filter design.But then the sampling rate is important so that you can plug the correct number into your filter design. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●October 17, 20152015-10-17
On Friday, October 16, 2015 at 3:57:46 AM UTC+13, Sharan123 wrote:> Hello, > > I am curious as to why sampling parameter is important while designing a > filter. I guess, it is sufficient that the original signal has been > sampled at a sufficient rate. > --------------------------------------- > Posted through http://www.DSPRelated.comEverything needs to be with respect to the sampling frequency so that your design works in the real world. Even if you simulate it you can have say unity fs and have a nyquest frequency of 0.5 a la Matlab.
Reply by ●October 17, 20152015-10-17
>Feel free to reiterate your question if you need to.Dear Tim, What happens if one has access to sampled data and you have not control or information about the system which was used to sample. All you know is, sampling was done at sufficient rate. Probably, very hypothetical question, but what are the implications of using incorrect sampling value while designing a filter. --------------------------------------- Posted through http://www.DSPRelated.com
