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

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Translation invariance in max-pooling and cascading with convolutional layer

I am reading through this page about convolutional neural networks and I am confused about the part about max-pooling (downsampling a signal/image with the maximum value in a block). Apparently, one ...
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16 views

Optimal signal sampling reduction method : Decimation, interpolation or both?

I have a function with an equation: \begin{equation} C(t)=1.6925\left(\exp^{-0.136t}- \exp^{-1.192t} \right) u(t) \end{equation} where u(t) is a unit-step function. Then, denoting the Fourier ...
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21 views

Downsampling and Gaussian filtering in the context of scale space pyramids

In the context of scale space image pyramids using Gaussian filters I noticed that it's common to downsample the image after blurring with $\sigma = 2*\sigma_{init}$ . My question is: What is the ...
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2answers
34 views

Reconstruction of bandpass filtered signal from decimated version of itself

I know how to up-sample a discrete, real signal (by an integer factor n) that is band-limited to frequencies between $f_1 = 0 \mathrm{Hz}$ and and $f_2$: Just insert $n-1$ zeros between every original ...
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1answer
43 views

Upsample - filter - downsample

Given a discrete signal $ r(nT_c)$ specified at a rate $T_c$, assume we want to resample with a 3/2 rate change to match the sampling rate of some other signal. We would like to upsample it by 3, ...
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8 views

How to do carrier recovery from base band data

Hi I am developing the carrier recovery model for QPSk demodulation. I am planning to use a IQ demodulator IC and bringing the 720MHz IF signal to baseband data of 320 Mbps each channel 160 Mbps. Now, ...
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33 views

How to show the time history of a signal down-sampled ? under the rate of 25Hz & 40Hz and find its DFT analysis?

How to show the time history of a signal down-sampled under the rates of 25Hz & 40Hz and find its DFT analysis using Matlab ? The sample signal is in a data file (sensor_data.mat) its sampling ...
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63 views

Downsampling an Oversampled packet

I have series of amplitudes of a signal recieved at center frequency of 433.9MHz, sampling at 250000 Hz. I can see the information received is the packet I am after, just sampled too high. I believe ...
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206 views

What is the most precise frequency analysis spectrography algorythm?

Everyone uses Fast Fourier Transform, which is fast at the detriment of precision. The input audio has sample accuracy and the FFT has 1/64 sample accuracy. What algorithms can output high resolution ...
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1answer
34 views

Why does downsampling increase the phase angle of poles in autoregressive models?

When reading about autoregressive models (AR), people often "downsample to increase the phase angle of the poles of the corresponding transfer function". How exactly does downsampling affect the ...
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15 views

Quantitatively assess downsampled data vs original data

I have a dataset that is prohibitively large to work with in its raw state. I want to try different methods of downsampling to accelerate analysis, but need to be able to compare that reduced result ...
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26 views

How can I make the mean of samples be approximately equal to the mean of actual continuous signal?

Suppose there is signal $f(t)$ that is continuous and periodic. It is known that this $f$ is $T$-periodic. (but it's not necessarily a single cosine $f(t)$.( I'd like to make the mean of samples be ...
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2answers
87 views

Downsampling, Filtering and Averaging

I have a signal of bandwidth DC to ,say, 100 Hz. I am interested in the range DC-10 Hz. I oversample by a factor of, say, 30. Thus the sampling rate is 600 samples/sec. Then I bandpass filter and ...
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33 views

Image warping with subpixel accuracy

I am trying to test the sub-pixel accuracy of an optical flow method and need to generate some synthetic data to do so. I start with an image $I_0$, which is a Perlin noise image and a set of ...
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1answer
88 views

Difference between subsampling and downscaling (image)?

I know that there are many ways to upscale (interpolate) an image using bilinear, bicubic, sinc... Somehow, these same algorithms can also be used to downscale an image. But when it comes to ...
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38 views

What's the use case and explanation of frequency-domain subsampling?

In my solution to a certain problem I use subsampling in the frequency domain. Amazingly, it produces good results. Is it really that awkward to see subsampling in frequency domain? What the ...
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1answer
38 views

How does sampling and subsequent resampling affect aliased harmonics?

If I sample a signal with a harmonic higher than half my sample frequency I can predict the aliased frequency easily as $$|F_h-kF_s|$$ But what if after sampling the signal, I re-sample at a lower ...
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2answers
176 views

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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2answers
147 views

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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1answer
36 views

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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2answers
79 views

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 ...
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97 views

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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80 views

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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326 views

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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247 views

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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40 views

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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106 views

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. ...
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1answer
43 views

Downsampling MP3 for FM broadcast

I have some MP3s that are encoded at 44.1kHz with a bitrate of 160kbps. I hook these up to my car using an FM transmitter and the sound quality isn't particularly great. Low and high notes sound ...
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4answers
154 views

up sample and down sample

Let's say that I have a sampled signal x[n], it is being, in this exact order, up sampled by 2, down sampled by4, up sampled by 4 and down sampled by 2 to produce y[n]. It seems to me that it should ...
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67 views

Image getting completely white on downsampling

I performed an image downsampling with averaging operation(The image is divided into 2 by 2 blocks,then it is downsampled by 4 times.New pixel values od downsampled image is replaced with the mean of ...
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3answers
142 views

Decimate/downsample a signal from 1920.93Hz to 1920Hz. Possible? [duplicate]

I've just learned that the A/D converter I am using is not sampling at my desired sampling rate. I request 20 seconds of data at 1920Hz and I receive 38400 points of data that were actually sampled ...
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360 views

Why need an low pass filter after up-sampling? [duplicate]

I understand why there need an low pass filter before down-sampling, the sample frequency need to be at least twice of the max frequency signal, else there will be ...
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144 views

Effects of sampling rate approaching the Nyquist frequency? (not undersampling)

I understand that you need to sample at a frequency greater than or equal to the Nyquist frequency to reconstruct a signal/aliasing etc. I read though that a "more conservative" approach is to sample ...
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396 views

Trying to understand downsampling and then upsampling

I am trying to understand how this works, specifically, what the DTFT of each step looks like in each step of the chain (for understanding). I am not looking for an answer like because the input ...
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3answers
215 views

How to display the output as the input with a fractional delay? [closed]

I am trying to introduce a fractional delay in my input vector x[n] so the output is something like y[n]=x[n-M/N]. I am not supposed to use the MATLAB fracdelay function.So, I used sampling and delay. ...
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7answers
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Downsampling/Decimation - When is well done?

I am working on decimation of signal, and I want to know which is the best way to understand if the downsampling is well done or not. At the moment I am comparing the FFT of the source signal and the ...
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1answer
94 views

A question on filters

I am fairly new to DSP have been reading up on digital filters and have a few questions. I have a signal with very high frequencies whose DC component i want to estimate. The magnitudes of these ...
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1answer
138 views

Downsampling oversampled image (smallest size which retains image 'detail' within acceptable limits)

I have a large collection of oversampled images (family photos of varying 'sharpness' scanned at a uniformly high dpi) and would like to downsample them to optimise storage space whilst retaining ...
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76 views

Create an aliased image in FD

Is there an accurate way to create an aliased image from the Fourier transform of the original image? in other words, i have the Fourier coefficients of an image and i want to make down-sample in ...
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92 views

Downsampling a PSD that was generated by zero-padding - worth it?

Let us say we have a signal $y(k)$ that is of length $K$. I can compute its PSD, also of length $K$. Let us say that this length was not good for finding peaks, so I computed a PSD that was of length ...
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93 views

Reducing frequency of a signal

I have a signal that I want to make it sound like a whisper. This is probably better than using a voice conversion system, but I was just want to do some experimenting before. I was thinking maybe ...
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168 views

Direct IQ sampling symbol transition problem

In a direct sampling RF front-end, we can get real samples. But when we sample the signal with two ADC with a sampling delay $ \frac{4n+1}{4fc}$ where $n$ can be $0,1,2 \dots$ Then we have In phase(I) ...
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65 views

Preserving integral through downsampling

I've got a high-resolution image segmentation, which I'm downsampling (and non-linearly deforming) to fit on an ROI image. I typically blur the high-res image before downsampling with a Gaussian-fwhm ...
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182 views

Most efficient way to downsample a signal by a factor of 2.5x

I know that to downsample by a factor of 2.5x one can upsample a signal by a factor of 2 and downsample by a factor of 5. I am wondering what is the best and more efficient way of downsampling by a ...
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1answer
1k views

CIC Filter vs Simple Downsampler

I' trying to implement a QPSK modulation/demodulation. At one point I have to decimate my signal by 4 for an easier implementation. I've read everywhere that the best way to do it is to use a CIC ...
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2answers
879 views

Decimation of signal. How to plot frequency spectrum

I have an FDM signal from 0 to 70 MHz. The total signal contains 4 FDM signals from (0-fs/4), (fs/4-fs/2), (fs/2-3fs/4) & (3fs/4-fs). I used fvtool command in matlab to plot these signals. Then i ...
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1k views

Downsampling - upsampling FFTW

I'm having 2 signals which have different sampling rates i.e., 1ms(A) and 4ms(B) and I've tried to upsample/downsample either of the signals based on the code snippet Resampling based on FFT which I ...
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714 views

Oversampling then filtering and downsampling

Currently I'm working on a project to record ELF (Extremely Low Frequency) signals from a receiver. The highest frequency of interest is about 30 Hz and the system should have a flat frequency ...
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181 views

Downsampling and Gradient filtering

Are the following sequence of operations the same - Down-sampling filtering followed by gradient filtering with kernel [-1 0 1] Gradient filtering with kernel [-1 0 1] followed by down-sampling ...
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4answers
4k views

How can I resample a signal with an arbitrary factor (e.g. 128000Hz to 16000.1Hz) in Matlab?

I need to simulate the sampling of a continuous (fsCtu = 128000Hz), acoustic signal with two microphones that have a slight offset in sampling rate (fsMic1 = 16000, fsMic2 = 16000.1) in Matlab. What ...