Reply by Erik de Castro Lopo●January 18, 20042004-01-18
Fred Marshall wrote:
>
> "Jim Thomas" <jthomas@bittware.com> wrote in message
>
> > There's a good resampling tutorial (and source code) here:
> > http://www.dspguru.com/info/faqs/mrfaq.htm
>
> The above is a good reference if the sample rates have a rational
> relationship. So, it is possible to adjust the sample rates, or one of
Secret Rabbit Code is a library for sample rate conversion of audio signals.
It is capable of conversion between arbitrary ratios and even time varying
ratios. It is released under the terms of the GNU General Public License
and is available here:
http://www.mega-nerd.com/SRC/
Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo nospam@mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"In civilian equipment, such as computers, the number
of components alone makes miniaturization essential if
the computer is to be housed in a reasonable-sized
building." Electronics Oct. 1, 1957, p. 178
Reply by Fred Marshall●January 13, 20042004-01-13
"Jim Thomas" <jthomas@bittware.com> wrote in message
news:10082i4s5s6fv37@corp.supernews.com...
> tanh wrote:
> > Hello,
> >
> > I'm trying to add 2 different digital waveforms together, but the 2
> > are sampled at different rates..
> >
> > Logically, first I must resample them to another common sampling rate,
> > but.. how should I go about it? Can I reconstruct the analog waveform
> > and then resample at the desired sampling rate?
> >
> > If my priority is to preserve the frequency content, can I just simply
> > use some sort of curve fitting to reconstruct the waveform? What sort
> > curve fitting is best to use?
> >
> > What other methods can I do this? What are the considerations that I
> > must look out for?
> >
> > Thanks in advance!
> >
> > Regards,
> > Tanh
>
> There's a good resampling tutorial (and source code) here:
> http://www.dspguru.com/info/faqs/mrfaq.htm
The above is a good reference if the sample rates have a rational
relationship. So, it is possible to adjust the sample rates, or one of
them, to end up with the same rate on both. If this isn't the case, then
you'd need to interpolate - which is the simple way of "going back to
continuous" without going all the way. Interestingly, sample rate
modification upward and interpolation are the same operation if the
interpolation ratio is a rational fraction. If it isn't then some other
method of interpolation will be necessary on one of the signals.
I've often wondered how various numerical curve fitting interpolation
methods affect the frequency content - haven't researched it. There must be
some papers on the subject however. There are papers that develop spectral
signal to noise ratio for various interpolation methods - so that approach
gets to the question. Whether a wide enough variety of methods has been
studied in this manner I don't know.
If you had lots of time and memory you might just interpolate up to some
very high rates that are close and then do some very simple interpolation on
one signal. Then the maximum interpolation distance would be 1/2 a sample
interval. Eventually as the sample rate gets very high, linear
interpolation could be acceptable and 2nd order would probably be quite
good. As to the functions used for interpolation, I wonder what happens if
you use 2 sincs centered and weighted by the adjacent samples? I'd expect
that to be pretty good at the edges and worst at the midpoint. At the
midpoint it might take 4 or 6 or 8 or ..... I don't know how many but you
could calculate it. For that matter if you used sin^3(x)/x^3 at each
sample then the number of terms would be smaller because of the more rapid
decay of the terms.
Maybe someone else knows more about this....
Fred
Reply by Jim Thomas●January 13, 20042004-01-13
tanh wrote:
> Hello,
>
> I'm trying to add 2 different digital waveforms together, but the 2
> are sampled at different rates..
>
> Logically, first I must resample them to another common sampling rate,
> but.. how should I go about it? Can I reconstruct the analog waveform
> and then resample at the desired sampling rate?
>
> If my priority is to preserve the frequency content, can I just simply
> use some sort of curve fitting to reconstruct the waveform? What sort
> curve fitting is best to use?
>
> What other methods can I do this? What are the considerations that I
> must look out for?
>
> Thanks in advance!
>
> Regards,
> Tanh
There's a good resampling tutorial (and source code) here:
http://www.dspguru.com/info/faqs/mrfaq.htm
--
Jim Thomas Principal Applications Engineer Bittware, Inc
jthomas@bittware.com http://www.bittware.com (703) 779-7770
Time flies like an arrow. And fruit flies like bananas.
Reply by tanh●January 13, 20042004-01-13
Hello,
I'm trying to add 2 different digital waveforms together, but the 2
are sampled at different rates..
Logically, first I must resample them to another common sampling rate,
but.. how should I go about it? Can I reconstruct the analog waveform
and then resample at the desired sampling rate?
If my priority is to preserve the frequency content, can I just simply
use some sort of curve fitting to reconstruct the waveform? What sort
curve fitting is best to use?
What other methods can I do this? What are the considerations that I
must look out for?
Thanks in advance!
Regards,
Tanh