Hi all, As I know there are two interpolation method: 1. As many DSP book said, pading (L-1) zero points into space between two primitive samples, then lowpass filter it. Then we get the result. 2. linear cubic langerange interpolation. What is difference between those two method? Which has better performance? As my understanding first method always apply to the rational number upsample (include L or L/M). The second method always apply to nonrational number upsample. Am I right? When rational nember upsampling, two method can be used. The performance of first method depends on the lp filter. If the filter has perfect frequency response the first method will achieve optimal performance. Whereas the performance of second method depends on the numbers of interperlation (8th langerange interpolation achieve better than 4th langerange interpolation). Am I right? Is there any quantantive relationship between taps of lp filter and number of langerange interpolation? _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

# compare of two interpolation method

Started by ●April 23, 2007

Reply by ●April 23, 20072007-04-23

On Apr 23, 2:03 pm, "HouYongmin" <houyong...@hotmail.com> wrote:> As I know there are two interpolation method: > > 1. As many DSP book said, pading (L-1) zero points into space > between two primitive samples, then lowpass filter it. Then we get the > result. > > 2. linear cubic langerange interpolation.well, there are many more than only these two.> What is difference between those two method? Which has better > performance? > > As my understanding first method always apply to the rational number > upsample (include L or L/M). The second method always apply to nonrational > number upsample. Am I right? > > When rational nember upsampling, two method can be used. The > performance of first method depends on the lp filter.both of these methods have an impulse function and corresponding LPF of which the performance (usually the stop-band attenuation) can be compared. in a sense, Hou, there *are* two fundamental methods of interpolating (of which there are many variants of each). the rational number interpolation is really upsampling by a known _integer_ and then decimating (downsampling by another integer) by picking out the samples you want (the samples you do not want are best not calculated in the first place). this is polyphase filtering and the sample-rate conversion (SRC) ratio *is* a rational number and you are restricted to that (meaning the interpolated times land exactly on the sampling instances of the intermediate upsampled signal). however, you can use opitimization like Parks-McClellan algorithm to design a really good LPF and pick out the interpolation coefficients from the FIR that results. that finite set of FIR coefficients would live in a table somewhere. interpolating using Lagrange or Hermite or B-spline or any other polynomial interpolation is when your new sampling instances can be *any* value of time; not restricted to integer values of your upsampled signal. actually linear interpolation and drop-sample interpolation are 1st and 0th order polynomial interpolation. from knowing the interpolating polynomial, you can determine a continuous- time impulse response and from that, a frequency response of an LPF to judge the quality of interpolation. i can send you a few papers describing some of this if you want. now these two methods can be combined: upsample by an integer ratio of 128 or 256 or 512 and then interpolate, using a polynomial, the adjacent micro-samples. usually linear interpolation is fine. r b-j

Reply by ●April 24, 20072007-04-24

Method 1 uses sinc function as its core (assuming rectangular window is used), while method 2 uses cubic Lagrange.>Hi all, > > As I know there are two interpolation method: > > 1. As many DSP book said, pading (L-1) zero points into space >between two primitive samples, then lowpass filter it. Then we get the >result. > > 2. linear cubic langerange interpolation. > > > What is difference between those two method? Which has better >performance? > > As my understanding first method always apply to the rationalnumber>upsample (include L or L/M). The second method always apply tononrational>number upsample. Am I right? > > When rational nember upsampling, two method can be used. The >performance of first method depends on the lp filter. If the filter has >perfect frequency response the first method will achieve optimal >performance. Whereas the performance of second method depends on the >numbers of interperlation (8th langerange interpolation achieve better >than 4th langerange interpolation). Am I right? > > Is there any quantantive relationship between taps of lp filterand>number of langerange interpolation? > > > > > > > > >_____________________________________ >Do you know a company who employs DSP engineers? >Is it already listed at http://dsprelated.com/employers.php ? >_____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?