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Upsampling and interpolation, downsampling and decimation Summary The terms Interpolation and Upsampling are used inconsistently in DSP literature. Sometimes, they are used as synonyms, and the meaning depends on the context.
The same applies to Downsampling and Decimation. |
The following definitions are used throughout this web page:
Upsampling Figure 1: Original waveform |
Figure 1 shows samples (black) of a continuous-time waveform (blue).
Three zero samples are inserted for every sample, upsampling it by a factor of four.
The result is shown in Figure 2.
Figure 2: Upsampling by four |
| Upsampling: Insertion of zero samples without filtering. |
Upsampler | Interpolation The waveform from Figure 2 is now lowpass filtered using an ideal lowpass.
The cutoff frequency is the highest possible frequency component from the original signal in Figure 1.
The result is shown in figure 3:
Figure 3: Interpolation with a factor of four |
| Interpolation: Insertion of zero samples and filtering. |
Interpolator | Downsampling Downsampling: Removing  samples every  samples. |
Downsampler |
Decimation
| Decimation: Filtering according to the highest possible frequency at the output bandwidth, and downsampling |
Decimator |
References The definitions are used for example in Oppenheim&Schafer, or Fred Harris' “Multirate Signal Processing”.
© Markus Nentwig 2007-2008
The content of this page is provided without any warranty and may not be reproduced without permission.
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mnentwig@elisanet.fi
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