Does Upsampling or Downsampling Change the Frequency content

[lordsathish]

upsampling and downsampling

Hi ppl,
Does Ups ampling or Down sampling a signal change its frequency content.
Since Up sampling increase the number of zero valued samples in the signal i think it should decrease the DC content of the signal. And again as Up sampling increase
both the sampling frequency and number of samples in the signal i think it should
not affect the frequency content of the signal since in a FFT the frequency domain values are k*Fs/N.
Please do tell me if my views are right...?

 

[ring0]

downsampling and upsampling in frequency

In order to upsample properly, the signal after adding zeroes should be passed through a digital low-pass filter.

https://en.wikipedia.org/wiki/Upsampling

In the case when an ideal low-pass filter is used, the spectrum will be unchanged, as it should be (only scaled along frequency axis).

 

[gabin]

what is the purposes of upsampling

up and down sampling is the process of changing the sampling rate of the signal.

 

[FvM]

frequency content of a signal

You can say, that upsampling (without a filter or interpolation) actually doesn't change the frequency content. The image around 0.5 fs in the higher sampling frequency signal representation is also present at 1.0 fs in the upper spectrum, but outside the presented range. However, the purpose of upsampling usually is in (almost) removing images within the nyquist range, and this implies interpolation respectively a lowpass filter.

 

[jetset]

sine2 frequency content

Downsampling and upsampling means shift in frequency by the dicrete time Fourier frequency shift property :

e^(jωon)x <-> X(e(jω-ωo))

so we may say that yes, they do change frequency content compared to the signal with no change at sampling...

 

[Petre Petrov]

how does the spectrum change with sampling

lordsathish Does Upsampling or Downsampling Change the Frequency content

Hello!
If you increase the sampling frequency Fd you are decreasing all errors (all differences between the sampled signals and the obtained samples).
Please note that you should increase also the number of the used bits n for coding the samples.
If is advisable to works with signal sampling factor (SSF) N>=4.

You could find some evaluation for the sinusoidal and co-sinusoidal signals here:
“A New Approach to Sampling Sinusoidal and Cosinusoidal Signals”, P T Petrov,
https://www.ieindia.org/pdf/88/88ET104.pdf

Also may be it will be useful to know:
“Sampling of the Simplest Signals”, P T Petrov
https://www.ieindia.org/pdf/89/89CP109.pdf

I hope that is helpful to you in some cases.
BR