Suodatin Pussi wrote:
> Janey wrote:
>> Hi All,
>> 
>> This query is related to data resampling. I have an ADC whose sampling
>> frequency is 40Mhz now I need two different version of resampled data
>> one being data resampled at 20Mhz while the other being at 22Mhz.
>> Could any one please tell me what would be the best way of doing the
>> resampling of data obtained from the ADC.
>> 
>> Thanking you,
>> 
>> Regards
>> 
>> Janey
> A Fir approach:
> For up 11 you add 10 zeros to each sample and fir-filter the signal.
> Since multiplying with zeros will result in zero output, you can skip
> these calcs. Basicly you're multiplying each sample with every 11th
> filter coefficient (startpoint however differs, depending on overlap).
> For down 20 you throw away 19 out of every 20 filtered samples, so you
> could have skipped these calcs and start the fir at every 20th sample.
> The best thing is to draw it out on paper.
> Don't forget so gain the signal with the upfactor. Since instead of
> adding zero's you actually should have repeated each sample 11 times.
> The fir filter should have a lp cuttoff for the lowest fs (its doing
> both cutoff and interpolating).
Using a FIR approach you actually do not up 11 or down sample 20 the
signal. It's more like interpolating the signal with 11/20th (you do not
have a large intermediate signal). But thinking as if you upsample and
downsample makes it easier to understand the mechanism.
Instead of adding zero's you could repeat a sample 11 times. Sincs
they're all the same in value you just can sum all corresponding FIR
coeffients and multiply it with the sample value. From the summed FIR
coeffs you could make a table.
But thinking in therms

In article <ed172f93.0406152009.1602d7c5@posting.google.com>,
Janey <janeyup@lycos.com> wrote:
>This query is related to data resampling. I have an ADC whose sampling
>frequency is 40Mhz now I need two different version of resampled data
>one being data resampled at 20Mhz while the other being at 22Mhz.
>Could any one please tell me what would be the best way of doing the
>resampling of data obtained from the ADC.

You probably want to low-pass filter for both new sampling rates to
avoid aliasing unless the original signal is already appropriate
(e.g. already has no components above 10MHz or 11Mhz).

You can use a windowed sinc interpolator for the 22MHz interpolation.
On a fast computer you can calculate the taps on the fly, or save them
into a hash table as needed.  No need to upsample.


IMHO. YMMV.
-- 
Ron Nicholson   rhn AT nicholson DOT com   http://www.nicholson.com/rhn/ 
#include <canonical.disclaimer>        // only my own opinions, etc.

Janey wrote:
> Hi All,
> 
> This query is related to data resampling. I have an ADC whose sampling
> frequency is 40Mhz now I need two different version of resampled data
> one being data resampled at 20Mhz while the other being at 22Mhz.
> Could any one please tell me what would be the best way of doing the
> resampling of data obtained from the ADC.
> 
> Thanking you,
> 
> Regards
> 
> Janey
A Fir approach:
For up 11 you add 10 zeros to each sample and fir-filter the signal.
Since multiplying with zeros will result in zero output, you can skip
these calcs. Basicly you're multiplying each sample with every 11th
filter coefficient (startpoint however differs, depending on overlap).
For down 20 you throw away 19 out of every 20 filtered samples, so you
could have skipped these calcs and start the fir at every 20th sample.
The best thing is to draw it out on paper.
Don't forget so gain the signal with the upfactor. Since instead of
adding zero's you actually should have repeated each sample 11 times.
The fir filter should have a lp cuttoff for the lowest fs (its doing
both cutoff and interpolating).

Janey wrote:
> Hi All,
> 
> This query is related to data resampling. I have an ADC whose sampling
> frequency is 40Mhz now I need two different version of resampled data
> one being data resampled at 20Mhz while the other being at 22Mhz.
> Could any one please tell me what would be the best way of doing the
> resampling of data obtained from the ADC.
> 
> Thanking you,
> 
> Regards
> 
> Janey


You may want to peek at Secret Rabbit Code.

www.mega-nerd.com

Hi Jim,

Thanks for your informative response.

Regards
Janey

Jim Thomas <jthomas@bittware.com> wrote in message news:<10d0kneft1ccd82@corp.supernews.com>...
> Janey wrote:
> > Hi All,
> > 
> > This query is related to data resampling. I have an ADC whose sampling
> > frequency is 40Mhz now I need two different version of resampled data
> > one being data resampled at 20Mhz while the other being at 22Mhz.
> > Could any one please tell me what would be the best way of doing the
> > resampling of data obtained from the ADC.
> > 
> > Thanking you,
> > 
> > Regards
> > 
> > Janey
> 
> Read the Multirate FAQ at DSPGuru:
> 
> http://www.dspguru.com/info/faqs/mrfaq.htm
> 
> For the 20MHz, you'll need to decimate by two.  For 22MHz, you'll need 
> to interpolate by 11 and then decimate by 20.  There are a lot of ways 
> to reduce the computations involved, but those are spelled out pretty 
> well in the FAQ.

Hi Honglei,

Thanks for your informative response.

Regards
Janey

"Honglei Chen" <hchen@mathworks.com> wrote in message news:<capecq$ov5$1@fred.mathworks.com>...
> Just use decimator afterwards.  The 20MHz one should be easy, just directly
> downsampling by 2.  The 22Mhz one, since is not a integer, may require
> upsampling first and then down sampling.
> 
> 
> "Janey" <janeyup@lycos.com> wrote in message
> news:ed172f93.0406152009.1602d7c5@posting.google.com...
> > Hi All,
> >
> > This query is related to data resampling. I have an ADC whose sampling
> > frequency is 40Mhz now I need two different version of resampled data
> > one being data resampled at 20Mhz while the other being at 22Mhz.
> > Could any one please tell me what would be the best way of doing the
> > resampling of data obtained from the ADC.
> >
> > Thanking you,
> >
> > Regards
> >
> > Janey

Janey wrote:
> Hi All,
> 
> This query is related to data resampling. I have an ADC whose sampling
> frequency is 40Mhz now I need two different version of resampled data
> one being data resampled at 20Mhz while the other being at 22Mhz.
> Could any one please tell me what would be the best way of doing the
> resampling of data obtained from the ADC.
> 
> Thanking you,
> 
> Regards
> 
> Janey

Read the Multirate FAQ at DSPGuru:

http://www.dspguru.com/info/faqs/mrfaq.htm

For the 20MHz, you'll need to decimate by two.  For 22MHz, you'll need 
to interpolate by 11 and then decimate by 20.  There are a lot of ways 
to reduce the computations involved, but those are spelled out pretty 
well in the FAQ.

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com          (703) 779-7770
In theory, theory and practice are the same, but in practice, they're not

Just use decimator afterwards.  The 20MHz one should be easy, just directly
downsampling by 2.  The 22Mhz one, since is not a integer, may require
upsampling first and then down sampling.


"Janey" <janeyup@lycos.com> wrote in message
news:ed172f93.0406152009.1602d7c5@posting.google.com...
> Hi All,
>
> This query is related to data resampling. I have an ADC whose sampling
> frequency is 40Mhz now I need two different version of resampled data
> one being data resampled at 20Mhz while the other being at 22Mhz.
> Could any one please tell me what would be the best way of doing the
> resampling of data obtained from the ADC.
>
> Thanking you,
>
> Regards
>
> Janey

Hi All,

This query is related to data resampling. I have an ADC whose sampling
frequency is 40Mhz now I need two different version of resampled data
one being data resampled at 20Mhz while the other being at 22Mhz.
Could any one please tell me what would be the best way of doing the
resampling of data obtained from the ADC.

Thanking you,

Regards

Janey