# Questions tagged [downsampling]

In signal processing, downsampling (or "subsampling") is the process of reducing the sampling rate of a signal.

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### Sample keypoint found in multi-scale to one scale (scale space with O octaves)

For a multi-scale keypoints detector, local extremas are found between the scales at EACH octave. The scale-space is implemented as follows: Each octave is downsampled by half from the first image in ...
3answers
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### Practical Applications of upsampling and downsampling

I'm a complete novice to digital signal processing, and I've started reading a few books on it. In particular, I've run across the concept of upsampling and downsampling. As I understand it, given a ...
2answers
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### Z-transform of a downsampler

In this paper or multirate filtering, the author establishes the following mathematical relationship. Let $y_D$ be the output of a downsampler such that $$y_D[n] = x[Mn]$$ where $M$ is the ...
2answers
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### Downsample Equiripple FIR filter

I am designing some Downsampling filters using the remez exchange algorithm (Matlab FDAtool). I see that some times i get a spike at the first and last coefficients. does anybody knows why is that? my ...
1answer
4k views

### Converting from stereo to mono by averaging

Hi I'm doing a past exam question about converting from stereo to mono. The scenario is below: The first question is: Explain why would this result in a noisy encoding. How is the noise introduced ...
1answer
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### Reference for Supersampling

I want to downsample images to arbitrary sizes using supersampling to avoid aliasing effect. The only two good explanations I found were on Wikipedia and everything2.com, but there are still gaps. ...
2answers
11k views

### How to extract vocal part from stereo audio signal?

I'm now processing MP3 file and encounter this problem. My MP3 is stereo encoded. What I want to do is extract vocal part for further processing(whatever mode of output signals, mono or stereo are ...
3answers
3k views

### Downsampling lowpass filter for audio: FIR or IIR?

I'm working on a real-time audio processing project in which I have to downsample a 44.1 kHz to a yet-to-be-determined lower sampling rate essentially for reducing computational complexity. I'm ...
3answers
5k views

### What is anti-alias pre-filter for preventing aliasing after under-sampling?

We know that the under-sampling results in aliasing and frequencies higher than half of the Nyquist rate is not distinguishable. I've a base band signal that I want to use the higher frequencies which ...
3answers
2k views

### What is the effect of aliasing on the magnitude of the autocorrelation?

I've a question about the effect of aliasing on the magnitude of autocorrelations. From a simulation in MATLAB, I don't see any effect of aliasing or any need to anti-alias filter when I take the ...
5answers
3k views

### Why would I leave a signal oversampled?

I can't think of a better way for asking this question so I will start with an example. Suppose that I have an input signal with a max frequency of 50Hz (sampled at 100Hz). Now the signals of interest ...