Questions tagged [downsampling]

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

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470 views

Decreasing Sample Rate in DFT (FFT) for Audio Analysis

I'm working with audio data analysis through FFT algorithm. My example audio is a sine wave at 440 Hz and 44100 Hz sampling rate. FFT methods in programming, like ...
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2answers
505 views

Downsampling from 100Hz to 60 Hz

I have two sensors measuring a single time varying signal . The first sensor (reference sensor) is sampling the data at 60 Hz and the second sensor (test sensor) is sampling the data at 60 Hz. I ...
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1answer
155 views

Downsampling in MATLAB - why scaling filter coefficients?

Trying to undertsand how MATLAB does resampling, looking at toolbox/signal/resample.m. This is the part where (downsampling) filter coefficients are calculated: <...
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1answer
57 views

Most natural interpolation to simulate increasing distance?

Background: I'm generating multiple datasets with varying scales of resolution to simulate taking pictures from varying distances and then comparing image classification performances. For example ...
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1answer
1k views

Downsampling audio for use in Machine Learning

I'm trying to use the work (Neural Networks) done in this repo: https://github.com/jtkim-kaist/VAD It says this: Note: To apply this toolkit to other speech data, the speech data should be ...
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1answer
96 views

Multirate Signal processing for matching DAC of the SDR

I have been breaking my head for a long time. Please help with this..any input would be helpful! I am trying to implement a OFDM system using SDR (USRPN210 for Transmitter and USRP2 for receiver) ...
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2answers
472 views

What is the effect of the natural logarithm in the frequency domain?

I have read that taking the natural logarithm of a signal $x$ in the time domain will introduce a spectral broadening and hence "up-sampling" process before the logarithm is required. I tried to test ...
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1answer
237 views

Downsampling a high pass filter

If I have an ideal high pass filter as the one in the picture: And I downsample it by 2, e.g. $h_{new}[n] = h[2n]$, is my understanding correct that the resulting filter would look like this in the ...
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1answer
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Python's $\tt resample$ vs $\tt resample\_poly$ vs $\tt decimate$

I have multiple signals each measured with a sampling rate 300Hz. They are mostly periodic, although there are some parts of some of the signals, that seem to be random and do not follow the rest of ...
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2answers
59 views

Explaining a statement regarding aliasing in a document

I am reading this document and in the section "Aliasing and Anti-Aliasing", the author make the following statement: Consider a signal with two frequency components: $f_1 = 10\,\text{Hz}$ which is ...
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0answers
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Downsampling and upsampling of a signal in Python

If I want to downsample a signal in Python, is it better to use method resample from SciPy Signal Processing module or method decimate from the same module? What is the difference between these two ...
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1answer
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How left out down-sampling in 3D-DWT just on the Z direction

I am working on image processing by a 3D wavelet transform. I have a problem with the classification size of the wavelet coefficients. As you know, when we apply 3D_DWT on the image (for example: ...
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1answer
449 views

Image zoom out using Gaussian blur and downsampling

I am trying to implement a simple zoom out algorithm using two steps: The image is blurred using gaussian convolution of standard deviation $0.8\sqrt{{\tt zoomfactor}^2-1}$ as we saw in class. The ...
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1answer
72 views

How does the bandlimit of an image reduce by an octave in Gaussian Pyramid procedure?

Reference paper 1. For arguments sake, let's say that the maximum and minimum frequency in an image are 256Hz and 1024Hz. When I perform filtering using the gaussian function, the "bandlimit" reduces ...
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1answer
657 views

Downsampling and convolution

(Code snippet with example below). In MATLAB, assume I have a long signal vector y (length N) that I wish to convolve with a ...
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1answer
1k views

Down sample incoming stream of data to plot a dynamic graph

I am working on a module where I need to plot ECG streaming data on a graph. This graph has configurable speed i.e. plot 1 heartbeat data sample within say 50mm,25mm, etc. For this, I am required to ...
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0answers
648 views

Synchronizing signals with different sample rates

I am relatively new to signal processing, so I am still missing some basic knowledge, but I am trying to improve as much as I can. I am trying to synchronize two signals with matlab using cross-...
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1answer
1k views

Downsampling: Mathematical derivation

The problem I am having is related to sample rate conversion and more precise to sample rate reduction. I have been working on the paper Interpolation and Decimation of Digital Signals Tutorial Review ...
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1answer
361 views

Is FIR decimation the fastest possible method for integer downsampling?

For a digital music synthesizer I am developing, I have a stream of incoming samples $x_i$ and would like to downsample by $M$ to obtain a stream of samples $y_{Mi}$. I am currently bandpassing the ...
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1answer
1k views

Downsampling in Matlab simple example

I'm trying to visualise downsampling in the frequency domain in matlab I take a simple sinusoid, perform an fft and plot a two sided spectrum. Then I downsample the time domain signal (...
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1answer
488 views

Derivation of downsampling in the frequency domain

I'm having some trouble with this derivation $$s_d = \begin{cases}1&\text{for}\quad m\quad\text{multiples of}\quad D\\ 0 &\text{otherwise} \end{cases}$$ then $s_d$ is somehow rewritten to: $...
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1answer
284 views

Downsampling by non-integer factor Filter requirement [duplicate]

I am trying to implement a logic to downsample data in non-integer factor.Lets say,converting 48Ksps to 1344 samples per second.Have two step implementation of upsample by K ,and downsample by L is in ...
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0answers
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Decimation function implemented in standard C [closed]

I'm thinking in a decimation C function. The prototype of the function is: decimate(int N, float input[], float r, float output[]) where N is the length of array ...
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2answers
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Is this signal perfect reconstructable?

The question is as follow: Let me do the analysis: The downroad first: \begin{align} X_1(z) &= z^{-1}X(z)\\ X_2(z) &= \frac{1}{2}\left\{X_1\left(z^\frac{1}{2}\right)+X_1\left(-z^\frac{1}{2}\...
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1answer
481 views

Shannon interpolation formula for downsampled data with an “almost ideal” low pass filter

Let $x[n]$ be a discrete time signal with DFT given by $X(f)=\sum_n x[n]e^{-2\pi inf}$ supported on $[-1/2M,1/2M]$ with $f\in[-1/2,1/2]$. I can then down-sample to get $y[n]:=x[nM]$. Then, let $$\...
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2answers
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Understanding audio downsampling code (JavaScript) and adapting to a different ratio

I inherited responsibility for some audio downsampling code that I don't fully understand: ...
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1answer
413 views

what is difference between Alias vs. down sampling? [closed]

could someone help me explain downsampling in the context of Nyquist–Shannon sampling theorem and tell the difference between Aliasing and downsampling.Also is downsampling and undersampling the same ?...
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1answer
174 views

upsampling and downsampling operator

I am trying to prove that for all $x,y \in l^{2}(\mathbb{R})$, it holds that $$\left\langle\left(\downarrow M\right)\left[x\right],y \right\rangle = \left\langle x,\left(\uparrow M\right)\left[y\right]...
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2answers
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Which order to perform downsampling and filtering?

I have EEG data recorded with 128Hz sampling rate. As my goal is to reduce the amount of data (and maybe noise), I want to downsample the data to 64Hz (I am only interested in range 0.5 - 30Hz). I ...
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0answers
96 views

Elementary proof of Fourier domain formula of multidimensional downsampling by $M$

I am trying to prove a well-know formula for the multidimensional downsampling by arbitrary downsampling integer matrix $M$ in $d$-dimensional case. The formula is $$ \hat{y}(\omega)=\frac{1}{\...
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1answer
553 views

Downsampling and filtering (convolution)

I have a discrete $2N$length signal $y[n]$ which I want to downsample by a factor of $F=2$. In order to avoid aliasing (since I assume that my original sampling rate is exactly equal to $2f_{max}$,i.e....
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135 views

With regards to multirate processing, what are the benefits of having a 'slower' sampled signal?

With regards to multirate processing, what are the benefits of having a 'slower' sampled signal? Let's say I have a continuous signal $$x(t) = \cos(2\pi\cdot3t) + \cos(2\pi\cdot 7t)$$ and it is ...
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2answers
796 views

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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1answer
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Aliasing after downsampling [duplicate]

Let me start with time domain representation of the original signal \begin{equation} x_n=\sum_{k=0}^{2N-1}X_ke^{j\frac{2\pi nk}{2N}} \end{equation} where $2N$ is number of time/frequency samples ...
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1answer
501 views

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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2answers
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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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1answer
99 views

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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2answers
398 views

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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1answer
2k views

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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2answers
388 views

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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2answers
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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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1answer
3k views

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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2answers
234 views

Question about decimation/downsampling

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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5answers
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Output gain when 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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1answer
1k views

Downsampling and Then Upsampling

Given this system: I need to show the $\mathcal Z$-transform of $y[n]$ as a function of the $\mathcal Z$-transform of $x[n]$. Now I know that for downsampling alone: $$Y(z) = \frac1M\sum_{m=0}^{M-1}...
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1answer
430 views

Cut-off frequencies for fractional sample rate adjustment

We have a signal sampled att 22 kHz that we want to interpolate to 40 kHz. So we can do this by upsampling by a factor 20, then downsampling by a factor 11. My question regards the choice of cut-off ...
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1answer
393 views

rtlsdr sample rates and nyquist rate

I have a rtlsdr dongle which apparently has a max sample rate of about 2.4 MHz. I'm wondering how it's possible to capture signals at say 900 MHz with this device. Doesn't the sample rate need to be ...
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1answer
468 views

Frequency Representation of Downsampled Signal

I'm trying to follow the steps from Oppenheim for the derivation of the frequency representation of a signal which is to be down sampled by a factor of M. It makes sense to me that: But then the ...
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0answers
116 views

Causal downsampling of a small buffer of GPS positions

Not sure this is the right place to ask, but I hope so. Context A GPS receptor is installed in a moving vehicle, and saves the measured positions with a resolution of at most $r_0$ to a small (a few ...
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1answer
461 views

Triangle-kernel filtering problems at non-integer ratios

I'm trying to implement image downscaling using a triangle filter (it's narrow therefore fast, and goes hand in hand with linear interpolation when upscaling), and the triangle function used for ...