# Tagged Questions

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

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### Fast/efficient way to turn real passband samples to complex baseband

I have real-valued samples of a bpsk signal i am receiving (see frequency spectrum in figure A), that I want to turn into complex samples for further processing. However when I just use the received ...
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### Aliasing after downsampling

Let me start with time domain representation of the original signal $$x_n=\sum_{k=0}^{2N-1}X_ke^{j\frac{2\pi nk}{2N}}$$ where $2N$ is number of time/frequency samples ...
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### Comb function and downsampling [duplicate]

I understand role of Dirac comb function in downsampling in theory but I have problem with showing it mathematically. Let me start with time domain representation of the $2N$ periodic original signal ...
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### Elegant way of calculating minimal sampling frequency without aliasing for annoying signals

Given a symmetric Fourier transform with finite support as below, there's an algorithmic procedure to determine the minimal frequency for sampling without aliasing: Find an integer $L>1$ ...
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### The difference of downsampling an image and smoothing an image?

I am, at the moment, trying to read up on some simple computer vision elements, in which i have become a bit comfused on the terms downsampling and smoothing, and whether there is a difference between ...
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### One-bit depth audio

I have a music player which is only able to play sound with one a bit-depth of one. I can produce this by taking a song and simply boosting the signal $+100\textrm{ dB}$. Is there another approach ...
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### Recovering a signal that was upsampled by non-integer factor

I have a data sequence $G[n]$ that is upsampled at the transmitter of a communication system by a non-integer factor ($1.5$ to be precise). At the receiver, I am supposed to downsample the data and ...
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### Gaussian Pyramid - How is Subsampling Rate Related to Sigma?

I found a gaussian pyramid implementation in a MOPS paper (feature detection). They use sampling rate $s=2$ and $\sigma=1$ - i.e. to generate a new level of the pyramid, the current level is smoothed ...
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### How does MATLAB's $\tt upfirdn$ select extra points when downsampling?

I had a signal 512 samples long and I used upfirdn to filter and downsample it by a factor of 2. I thought this would result in a 256 sample long variable, but ...
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### The relationship between downsampling and frequency resolution

I am having trouble understanding a concept that I have seen in many published papers. For example, in this paper (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0082748) they wrote ...
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### Random sampling vs uniform sampling

In this paper of Lustig, he speaks about a something which appears unintuitive: sampling at random may exhibit better performance than sampling uniformly. I tried to understand this starting from page ...
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I am using an on-chip SAR adc where for some reason I can only get accurate signal reconstruction and filtering when I sample at almost 100 times my desired sampling frequency. Specifically, the ...
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### Upsampling and downsampling

Do the processes of upsampling and downsampling affect the magnitude of the transform of a signal? And if not, why am I seeing everywhere that a filter with gain different from 1 is applied after up/...
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### trying to downsample audio

I am trying to downsample from 44100hz to 8000hz, and I am not sure what I am doing wrong here. 44100 / 8000 is 5.5125, so I am getting hung up a little on the fractional remainder which is causing ...
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### What if the Down sampling factor is not an integer?

I have developed a function which down samples an input signal.Say I have an input signal with a sampling rate of 512 samples/sec and would like to down sample it 128 samples/sec, then the down ...
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### Quadrature subsampling result not as expected

Let's suppose I have an ADC running at 81.824MHz. I am quadrature subsampling a signal that is at 143.5MHz using a sampling rate of 81.824MHz/4 = 20.456MHz = Fs. I expect the signal to appear at ...
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### up down sampling and low-pass filters

I am trying to figure out what seems very trivial thing about down sampling and up sampling. The problem that I am facing is how to find the effects of up sample on a signal followed by a filter and/...
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### down sampling and a factor of 2 without loss of information

I am trying to understand the limits of down sampling on a signal, i.e. how far can I go without loss of information or overlapping. It says in the solution manual of the Oppenhiem and Schafer book (...
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### Downsampling fft results to a graphics display

I'm new to dsp. I've got a complex signal that was sampled at 192kHz then an fft of 16384 bins created. This now needs to be plotted on a graph for a real time spectrum display. The problem is if ...
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### Downsampling PCM Audio

I'm looking everywhere for solutions for audio downsampling. However for one reason or another they are incomplete, sometimes buggy, and sometimes are in a programming language I cannot understand. ...
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### Is digital up and down sampling linear/causal/time-invariant?

So I am trying to determine whether the process of up sampling (zero padding) and downsampling are linear, causal and/or time-invariant. Based on some resources I found online, I am under the ...
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### What is a correct way to downsample an impulse train

So I have a signal which is caused by an impulse train. I can determine the impulse train with 500hz but sample my output signal with only 10hz. Then I want to calculate an impulse response function. ...
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### Perfect reconstruction ( Single Channel )

I was trying to solve the following problem . Given an input x[n], consider upsampling by 2, followed by interpolation with a filter having z-transform H(z) for magnification of the signal. ...