Problem in Sampling

Dear All,


I have one problem in real time signal processing. My signal frequency is
4000Hz and the sampling frequency is 8000Hz. Actually it should be more than
8KHz.

Becasue of that i am loosing the zero resting points of the sampled signal.

With out increasing the sampling frequency , is there any remedy for
avoiding the information loss ?

Thanking you,

Sai Kumar wrote:

> Dear All,
> 
> 
> I have one problem in real time signal processing. My signal frequency is
> 4000Hz and the sampling frequency is 8000Hz. Actually it should be more than
> 8KHz.
> 
> Becasue of that i am loosing the zero resting points of the sampled signal.
> 
> With out increasing the sampling frequency , is there any remedy for
> avoiding the information loss ?
> 
> Thanking you,
> 
> 
> 
> 
If your signal is centered around 4000Hz but is sufficiently low 
bandwidth you can sample at 7000Hz and get very good reconstruction.

But if your signal is DC to 4000Hz you're out of luck (but at least 
you're also saved from esoteric undersampling schemes).

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Hi Tim,
          Thank you,
          But i am unlucky as u said.

"Sai Kumar" <saikumar.s@in.bosch.com> wrote in message
news:cfheji$cv6$1@ns1.fe.internet.bosch.com...
> Dear All,
>
>
> I have one problem in real time signal processing. My signal frequency is
> 4000Hz and the sampling frequency is 8000Hz. Actually it should be more
than
> 8KHz.
>
> Becasue of that i am loosing the zero resting points of the sampled
signal.
>
> With out increasing the sampling frequency , is there any remedy for
> avoiding the information loss ?
>
> Thanking you,
>
>
>
>

On Fri, 13 Aug 2004 09:33:33 +0530, "Sai Kumar"
<saikumar.s@in.bosch.com> wrote:

>Dear All,
>
>
>I have one problem in real time signal processing. My signal frequency is
>4000Hz and the sampling frequency is 8000Hz. Actually it should be more than
>8KHz.
>
>Becasue of that i am loosing the zero resting points of the sampled signal.
>
>With out increasing the sampling frequency , is there any remedy for
>avoiding the information loss ?
>
>Thanking you,

Hi,
  your post sounds like you're sampling 
an analog 4 kHz pure tone (although you didn't actually 
describe your signal in a meaningful way), at a 
sample rate of 8000 samples per second.

Is that really what you're doing?

[-Rick-]

Rick Lyons wrote:
> 
> On Fri, 13 Aug 2004 09:33:33 +0530, "Sai Kumar"
> <saikumar.s@in.bosch.com> wrote:
> 
> >Dear All,
> >
> >
> >I have one problem in real time signal processing. My signal frequency is
> >4000Hz and the sampling frequency is 8000Hz. Actually it should be more than
> >8KHz.
> >
> >Becasue of that i am loosing the zero resting points of the sampled signal.
> >
> >With out increasing the sampling frequency , is there any remedy for
> >avoiding the information loss ?
> >
> >Thanking you,
> 
> Hi,
>   your post sounds like you're sampling
> an analog 4 kHz pure tone (although you didn't actually
> describe your signal in a meaningful way), at a
> sample rate of 8000 samples per second.
> 
> Is that really what you're doing?

Well, no he can't be doing that. He can't produce a perfectly pure tone
at exactly a steady 4KHz and he can't sample at a perfectly steady 8KHz
either. But that appears to be what he is trying to do, and now he is
wondering why he can't land his samples exactly on the zero state of
each wave. Or, maybe he is asking something else - who knows?

-jim


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Sai Kumar wrote:

> Hi Tim,
>           Thank you,
>           But i am unlucky as u said.
> 
> "Sai Kumar" <saikumar.s@in.bosch.com> wrote in message
> news:cfheji$cv6$1@ns1.fe.internet.bosch.com...
> 
>>Dear All,
>>
>>
>>I have one problem in real time signal processing. My signal frequency is
>>4000Hz and the sampling frequency is 8000Hz. Actually it should be more
> 
> than
> 
>>8KHz.
>>
>>Becasue of that i am loosing the zero resting points of the sampled
> 
> signal.
> 
>>With out increasing the sampling frequency , is there any remedy for
>>avoiding the information loss ?
>>
>>Thanking you,
>>
>>
>>
>>
> 
> 
> 
If your signal really has significant components from 0 to 4000Hz then 
you have no choice but to sample at greater than 8000Hz -- with real 
anti-aliasing filters you'll probably need to go much higher (16kHz 
would not be out of line).

I think you need to describe your problem more fully if you want help 
with it.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Hi Kumar - so you have frequencies between +/- 4000Hz present and you are
(complex?) sampling at 8000 samples per second ?  Why not filter prior to
sampling so you only have a small amplitude for frequencies around +/- 4kHz
and above?

"Sai Kumar" <saikumar.s@in.bosch.com> wrote in message
news:cfhi5q$otm$1@ns1.fe.internet.bosch.com...
> Hi Tim,
>           Thank you,
>           But i am unlucky as u said.
>
> "Sai Kumar" <saikumar.s@in.bosch.com> wrote in message
> news:cfheji$cv6$1@ns1.fe.internet.bosch.com...
> > Dear All,
> >
> >
> > I have one problem in real time signal processing. My signal frequency
is
> > 4000Hz and the sampling frequency is 8000Hz. Actually it should be more
> than
> > 8KHz.
> >
> > Becasue of that i am loosing the zero resting points of the sampled
> signal.
> >
> > With out increasing the sampling frequency , is there any remedy for
> > avoiding the information loss ?
> >
> > Thanking you,
> >
> >
> >
> >
>
>