Reply by Jeremiah Smith●September 9, 20032003-09-09
my main goal is to 'filter out' periodicities in a signal mixture. i know
the signal is composed of periodic waveforms, whose waveforms are the same
from period to period. I currently am only concerned with exact integer
periods for simplification.
I can detect one of the present periods reliably, but need to filter the
detected one out to detect the others. You mentioned the use of an IIR
filter - how exactly would it's impluse response look like in formula form?
"Alexey Lukin" <lukin@ixbt.com> wrote in message
news:b225ff4d.0309082159.180f93bd@posting.google.com...
> "Jeremiah Smith" <parlous@hotmail.com> wrote in message
news:<vlqf7o20qp4pc3@corp.supernews.com>...
> > i have tried a straight operation of adding the impulse responses
without
> > luck. the reason i want to try multiple impulses for one convolution is
>
> 1. You should concolve, not add impulse responses.
>
> > because if i do one period concolution at a time, the remaining signal i
can
> > use gets smaller and smaller. anyone know how to do this?
>
> 2. Probably this simple filter is not good enough for narrow notch
> filtering: it removes many other frequencies too. You can consider
> using narrower notches, e.g. IIR filters.
>
> Alex
Reply by Fred Marshall●September 9, 20032003-09-09
"Jeremiah Smith" <parlous@hotmail.com> wrote in message
news:vlqh9fcskoci67@corp.supernews.com...
>
> actually the impluse response is
>
> h(t) = q(t) - q(t - p)
>
> where q(t) is the unit impluse
>
> "Jeremiah Smith" <parlous@hotmail.com> wrote in message
> news:vlqf7o20qp4pc3@corp.supernews.com...
> >
> > i have an impluse response that is designed to remove periodicities from
a
> > signal as follows:
> >
> > h(t) = x(t) - x(t - p)
> >
> > where p is a period, and for this case p is an integer. i then use
> > convolution to get a remainder signal with the periodicity removed as
so:
> >
> > z(t) = conv( x(t), h(t) )
> >
> > i proceed then to get a final filtered signal by extracting the parts of
z
> > from z( p ) to z( max - p ).
> >
> > This is fine for a single period, but suppose i want to remove two or
more
> > periodicities with one transfer function and one convolution operation?
> >
> > i have tried a straight operation of adding the impulse responses
without
> > luck. the reason i want to try multiple impulses for one convolution is
> > because if i do one period concolution at a time, the remaining signal i
> can
> > use gets smaller and smaller. anyone know how to do this?
>
The impulse response that you offer is defined as the difference between a
function x(t) and itself delayed or advanced in time. But, you didn't
define x(t). So that's a problem. It almost appears that x(t) is a signal.
If x(t) is a signal then the formulation doesn't take into account time
variations of amplitude of the periodic components (and by extension,
phase).
Otherwise, it's not clear what sort of a "system" h(t) represents. I
suppose "x(t-p)" could be the output of an adapted filter but then it
wouldn't be x(t-p) any more. The only thing that will generate x(t-p) is a
pure delay.
As suggested, an adapted filter might be a better bet than a pure delay ....
if that's what you meant, it's not at all clear.
Fred
Reply by Alexey Lukin●September 9, 20032003-09-09
"Jeremiah Smith" <parlous@hotmail.com> wrote in message news:<vlqf7o20qp4pc3@corp.supernews.com>...
> i have tried a straight operation of adding the impulse responses without
> luck. the reason i want to try multiple impulses for one convolution is
1. You should concolve, not add impulse responses.
> because if i do one period concolution at a time, the remaining signal i can
> use gets smaller and smaller. anyone know how to do this?
2. Probably this simple filter is not good enough for narrow notch
filtering: it removes many other frequencies too. You can consider
using narrower notches, e.g. IIR filters.
Alex
Reply by Jeremiah Smith●September 9, 20032003-09-09
actually the impluse response is
h(t) = q(t) - q(t - p)
where q(t) is the unit impluse
"Jeremiah Smith" <parlous@hotmail.com> wrote in message
news:vlqf7o20qp4pc3@corp.supernews.com...
>
> i have an impluse response that is designed to remove periodicities from a
> signal as follows:
>
> h(t) = x(t) - x(t - p)
>
> where p is a period, and for this case p is an integer. i then use
> convolution to get a remainder signal with the periodicity removed as so:
>
> z(t) = conv( x(t), h(t) )
>
> i proceed then to get a final filtered signal by extracting the parts of z
> from z( p ) to z( max - p ).
>
> This is fine for a single period, but suppose i want to remove two or more
> periodicities with one transfer function and one convolution operation?
>
> i have tried a straight operation of adding the impulse responses without
> luck. the reason i want to try multiple impulses for one convolution is
> because if i do one period concolution at a time, the remaining signal i
can
> use gets smaller and smaller. anyone know how to do this?
>
>
>
Reply by Jeremiah Smith●September 8, 20032003-09-08
i have an impluse response that is designed to remove periodicities from a
signal as follows:
h(t) = x(t) - x(t - p)
where p is a period, and for this case p is an integer. i then use
convolution to get a remainder signal with the periodicity removed as so:
z(t) = conv( x(t), h(t) )
i proceed then to get a final filtered signal by extracting the parts of z
from z( p ) to z( max - p ).
This is fine for a single period, but suppose i want to remove two or more
periodicities with one transfer function and one convolution operation?
i have tried a straight operation of adding the impulse responses without
luck. the reason i want to try multiple impulses for one convolution is
because if i do one period concolution at a time, the remaining signal i can
use gets smaller and smaller. anyone know how to do this?
Reply by Jeremiah Smith●September 8, 20032003-09-08
i have an impluse response that is designed to remove periodicities from a
signal as follows:
h(t) = x(t) - x(t - p)
where p is a period, and for this case p is an integer. i then use
convolution to get a remainder signal with the periodicity removed as so:
z(t) = conv( x(t), h(t) )
i proceed then to get a final filtered signal by extracting the parts of z
from z( p ) to z( max - p ).
This is fine for a single period, but suppose i want to remove two or more
periodicities with one transfer function and one convolution operation?
i have tried a straight operation of adding the impulse responses without
luck. the reason i want to try multiple impulses for one convolution is
because if i do one period concolution at a time, the remaining signal i can
use gets smaller and smaller. anyone know how to do this?