Hello, I have problem puting the rigth name on the rigth thing: --> In "Discrete-time signal processing" of Oppenheim and schafer : "In general, the operation of reducing the sampling rate (including any prefiltering) will be called downsampling" section 4.6.1 --> In "An overview of sigma-delta converters" in IEEE signal processing of january 1996 vol 13, no 1 it is say "The collective operation of low-pass filtering and downsampling is know as decimation" What is the exact word for just take one sample among N ? Decimation or downsampling What is the exact word for take one sample among N after prefiltering ? Decimation or downsampling
Decimation / downsampling
Started by ●February 14, 2004
Reply by ●February 14, 20042004-02-14
I think of of them as almost the same thing but with decimation being a part of downsampling. "Decimation" comes from the Roman method of punishment where a group of men were selected at random and every tenth one was killed - hence the "deci" part of the word. So I think of decimation in signal processing as the keeping of some of the original samples and throwing others away in some orderly fashion. I think of downsampling as the whole process of resampling at a lower sample rate which generally includes some kind of antialias filter followed by a decimation. Also downsampling may involve some interpolation followed by decimation to get to the desired rate. Imagine if you wanted the data sampled at 2/3 of its original rate. So here the overall down sampling can be done by a 3x upsampling, lowpass filtering and then decimation by two. Of course these steps can be combined into a poly phase method where the decimation becomes the orderly picking of outputs from different filters. IHTH, -- Clay S. Turner, V.P. Wireless Systems Engineering, Inc. Satellite Beach, Florida 32937 (321) 777-7889 www.wse.biz csturner@wse.biz "pardon_232000" <pardon_232000@yahoo.fr> wrote in message news:ef9acc9e.0402141028.41443d4b@posting.google.com...> Hello, > > I have problem puting the rigth name on the rigth thing: > > --> In "Discrete-time signal processing" of Oppenheim and schafer : > "In general, the operation of reducing the sampling rate (including > any prefiltering) will be called downsampling" section 4.6.1 > > --> In "An overview of sigma-delta converters" in IEEE signal > processing of january 1996 vol 13, no 1 it is say > "The collective operation of low-pass filtering and downsampling is > know as decimation" > > > What is the exact word for just take one sample among N ? Decimation > or downsampling > What is the exact word for take one sample among N after prefiltering > ? Decimation or downsampling
Reply by ●February 14, 20042004-02-14
"Clay S. Turner" <CSTurner@WSE.Biz> wrote in message news:TIuXb.21136$Bv3.13074@bignews3.bellsouth.net...> I think of of them as almost the same thing but with decimation being apart> of downsampling. "Decimation" comes from the Roman method of punishment > where a group of men were selected at random and every tenth one was > killed - hence the "deci" part of the word. So I think of decimation in > signal processing as the keeping of some of the original samples and > throwing others away in some orderly fashion. I think of downsampling asthe> whole process of resampling at a lower sample rate which generallyincludes> some kind of antialias filter followed by a decimation. Also downsampling > may involve some interpolation followed by decimation to get to thedesired> rate. Imagine if you wanted the data sampled at 2/3 of its original rate.So> here the overall down sampling can be done by a 3x upsampling, lowpass > filtering and then decimation by two.Really I meant 2x interpolation followed by 3x decimation. Sorry about the transposition. Of course these steps can be combined> into a poly phase method where the decimation becomes the orderly pickingof> outputs from different filters. > > IHTH, > > -- > Clay S. Turner, V.P. > Wireless Systems Engineering, Inc. > Satellite Beach, Florida 32937 > (321) 777-7889 > www.wse.biz > csturner@wse.biz > > > > "pardon_232000" <pardon_232000@yahoo.fr> wrote in message > news:ef9acc9e.0402141028.41443d4b@posting.google.com... > > Hello, > > > > I have problem puting the rigth name on the rigth thing: > > > > --> In "Discrete-time signal processing" of Oppenheim and schafer : > > "In general, the operation of reducing the sampling rate (including > > any prefiltering) will be called downsampling" section 4.6.1 > > > > --> In "An overview of sigma-delta converters" in IEEE signal > > processing of january 1996 vol 13, no 1 it is say > > "The collective operation of low-pass filtering and downsampling is > > know as decimation" > > > > > > What is the exact word for just take one sample among N ? Decimation > > or downsampling > > What is the exact word for take one sample among N after prefiltering > > ? Decimation or downsampling > >
Reply by ●February 14, 20042004-02-14
"pardon_232000" <pardon_232000@yahoo.fr> wrote in message news:ef9acc9e.0402141028.41443d4b@posting.google.com...> Hello, > > I have problem puting the rigth name on the rigth thing: > > --> In "Discrete-time signal processing" of Oppenheim and schafer : > "In general, the operation of reducing the sampling rate (including > any prefiltering) will be called downsampling" section 4.6.1 > > --> In "An overview of sigma-delta converters" in IEEE signal > processing of january 1996 vol 13, no 1 it is say > "The collective operation of low-pass filtering and downsampling is > know as decimation" > > > What is the exact word for just take one sample among N ? Decimation > or downsamplingIt's always correct to say that one is sampling at the reduced rate because it is as if the original sampling had been done at that lower rate. Whether it is proper to do this or not / i.e. whether it causes frequency aliasing or not / would be a matter of concern.> What is the exact word for take one sample among N after prefiltering > ? Decimation or downsamplingI would probably say "sample rate reduction by a factor of N" (with the assumption that the prefiltering was done as was done properly). I believe that decimation (by a factor of N) is also a common term. Downsampling might connotes something different although it might also be used and understood in the context you've given. Downsampling could also mean sampling where the objective is to do a frequency translation of a bandpass signal to a lower frequency. For example: A bandpass signal with <1kHz bandwidth centered at 10kHz is sampled at 1kHz in quadrature with I and Q clocks. There results I and Q sample streams at 1kHz each. The signal has been downsampled to the lowest possible frequency and rate at the same time. So, the essential differences are: Was the original signal bandlimited to <fs/2 or was it bandlimited to <fs/2N? If the former, then sampling at a lower rate would be problematic. If the former, then filtering so that the bandwidth is limited to fs/2N is necessary. If the latter, then sampling at a lower rate would be OK. If the latter, then prefiltering is unnecessary. Fred