changing sampling rate of filter coeficients
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From: turboii on 22 Sep 2009 07:27 I need to implement a particular filter that has 240 taps and it works/designed for a sampling rate of 125kHz. I want to change the sampling rate of the filter from 125kS/s to 250kS/s to match the the hardware I am using, which operates at 250kS/s if i run the filter as is (at 250kS/s), the spectrum of the filter is stretched by 2. Is there an easy way to modify the filter taps to change the filter's sampling rate?
From: Vladimir Vassilevsky on 22 Sep 2009 10:21 turboii wrote: > I need to implement a particular filter that has 240 taps and it > works/designed for a sampling rate of 125kHz. What is the purpose of this filter? Usually, a FIR filter with more then few dozens of taps indicates a lousy design. The task could be accomplished in more optimal way. > I want to change the sampling rate of the filter from 125kS/s to 250kS/s > to match the the hardware I am using, which operates at 250kS/s So the length is going to be 480 taps. Incredible. > if i run the filter as is (at 250kS/s), the spectrum of the filter is > stretched by 2. Is there an easy way to modify the filter taps to change > the filter's sampling rate? A dull bruteforce solution is increase the number of taps by the factor of 2 by sinc interpolation. The better way is usung two stages: one is the legacy filter, the other is the filter to upsample the result by the factor of 2. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: turboii on 22 Sep 2009 17:11 > >> if i run the filter as is (at 250kS/s), the spectrum of the filter is >> stretched by 2. Is there an easy way to modify the filter taps to change >> the filter's sampling rate? > >A dull bruteforce solution is increase the number of taps by the factor >of 2 by sinc interpolation. The better way is usung two stages: one is >the legacy filter, the other is the filter to upsample the result by the >factor of 2. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com > so to double the smapling rate, i would simply double the number of taps and interpolate between each coefficient? so for example, if my taps were: [3, 5, 10, 10, 5, 3] and i just used linear interpolation, the new coefficients would be: [3, 4, 5, 7.5, 10, 10, 10, 7.5, 5, 4, 3] is that correct? what is the advantage by using a sinc interpolator?
From: Tim Wescott on 22 Sep 2009 17:32 On Tue, 22 Sep 2009 16:11:40 -0500, turboii wrote: >>> if i run the filter as is (at 250kS/s), the spectrum of the filter is >>> stretched by 2. Is there an easy way to modify the filter taps to > change >>> the filter's sampling rate? >> >>A dull bruteforce solution is increase the number of taps by the factor >>of 2 by sinc interpolation. The better way is usung two stages: one is >>the legacy filter, the other is the filter to upsample the result by the > >>factor of 2. >> >> >>Vladimir Vassilevsky >>DSP and Mixed Signal Design Consultant http://www.abvolt.com >> >> > so to double the smapling rate, i would simply double the number of taps > and interpolate between each coefficient? so for example, if my taps > were: > [3, 5, 10, 10, 5, 3] > and i just used linear interpolation, the new coefficients would be: [3, > 4, 5, 7.5, 10, 10, 10, 7.5, 5, 4, 3] > > is that correct? Yes. > what is the advantage by using a sinc interpolator? For most filters, better performance because the sinc interpolator does a better job of retaining the frequency-domain characteristics of the filter. -- www.wescottdesign.com
From: Randy Yates on 22 Sep 2009 17:33
"turboii" <gtu89rx7(a)yahoo.com> writes: > [...] > what is the advantage by using a sinc interpolator? A more accurate frequency response. Model the interpolation as a convolution of the interpolating function (linear, sinc) with the upsampled coefficients. Convolution in time ==> multiplication in frequency, and the sinc interpolator has a rectangular frequency response. -- Randy Yates % "I met someone who looks alot like you, Digital Signal Labs % she does the things you do, mailto://yates(a)ieee.org % but she is an IBM." http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO |