Questions tagged [downsampling]

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

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The Effect of the Order of Downsampling and Smoothing on the Output

How do I prove or disprove: Smoothing an image with a 3x3 filter using full convolution and then downsampling an image by 2 produces the same result as downsampling an image by 2 and then applying ...
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5 votes
3 answers
554 views

Moving average before downsampling: effect on Nyquist frequency?

First the simple questions: Is there an effect on the Nyquist frequency when I apply a moving average filter on the raw data before I downsample? And what does this do to aliased frequencies? ...
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Downsample (aggregate) raster by a non-integer factor, using a Gaussian filter kernel

The task is to downsample (aggregate) a raster from 100m pixel size to 460m. The aggregation should be performed using a Gaussian filter. To better understand the task, I am following the paper ‘The ...
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How to apply a filter that prevents aliasing when reindexing a dataframe to a new datatime index

I have two dataframe and I want to reindex the second dataframe to the index of the first dataframe by downsampling it. This however creates alliasing and as a result an artificial flattening of the ...
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1 vote
2 answers
247 views

Why use sinc function to downsample an image in fourier domain?

I'm very confused about downsampling in image processing and the use of sinc function to do it. I read this post [1]: 2D Fourier downsampling some time ago that talked about my own doubt, that is to ...
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51 views

Downsampling a binary file

TEXBAT is a recorded dataset about spoofing scenarios for evaluating GPS signal authentication techniques. On this project, there are recorded GPS signals stored as complex 16- bit samples at a rate ...
5 votes
1 answer
173 views

Polyphase Decimation Filter parallel inputs

I have an FPGA that's streaming in samples from a high speed ADC. The FPGA clock rate cannot run at the sample rate, so the samples are streamed in parallel (4 samples per clock cycle). I'd like to ...
7 votes
2 answers
902 views

Downsample a signal by a non-integer factor

I have a signal with a sample rate of 8.9286 MHz and I want to downsample it to 500 kHz. Since 8.9286 is not an integer multiple of 0.5 I can't simply decimate. Which downsample techniques are ...
1 vote
1 answer
65 views

Does downsampling an image twice result in a "worse" (or different) image than downsampling once

I am working on a project where the input is a large high quality image (2560 x 1440 pixels), which is eventually scaled down a lot (256 x 256) and used as input to an ML model. For reasons that I won'...
0 votes
1 answer
56 views

reconstruct the low resolution signal before upsampling

When we upsampling a discrete 1d signal by 2x, we first interleave the signal by 0 and add zero padding, then pass through a low pass filter. low resolution signal [x1, x2, x3, x4] -> interleave 0 ...
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4 votes
1 answer
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Applying 2D Sinc Interpolation for Downsampling in the Fourier Domain (DFT / FFT)

Related to The Proper Way to Do Sinc Downsampling (DFT Downsampling) for Uniformly Sampled Discrete Signals with Finite Number of Samples, how can one apply Sinc downsampling in the DFT / FFT domain ...
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1 answer
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question about time delay of practical filter design with sampling frequency

most system have 48khz and if i have 40tap low pass fir filter that cutoff freuqency is 300hz, filter delay is 1/48000*20 = 0.0004s but the frequency resolution is very sparse and i think if the ...
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2 votes
1 answer
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Downsampling an image using sinc interpolation?

I have a discrete image of size $2^N \times 2^N$ which I would like to iteratively downsample to produce a pyramid with image sizes $2^k\times 2^k, \, k=0,\ldots,N$. That is, each subsequent image ...
2 votes
1 answer
70 views

Noise from irregular sampling pattern

In this paper the author says By using an irregular sampling pattern and filtering the irregular samples to create the pixels, featureless noise is produced from such high frequencies rather than ...
0 votes
1 answer
136 views

spectrogram of a (strongly) downsampled file

I downsampled an audio file to a very low sampling rate, 48hz. This is because I stored some information in the file, that are not really audio information but the audio format was convenient to use. ...
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2 answers
135 views

when is downsampling followed by upsampling shift invariant

i have a set of images that i need to send through an hourglass-type convolutional system. I understand convolutions are shift-invariant, so i will ignore them the question is then: If I downsample a ...
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How to change the samplimg rate with interpolation and decimation?

I have a wav file at a 44.1KHz. I'm trying to change the sampling frequency to 1.26MHz. For that, I need to use interpolation and decimation, and so I did, but I'm getting odd results back. It seems ...
0 votes
1 answer
93 views

EEG peaks do not get identified at the correct frequencies

For my thesis I am re-analyzing a dataset where subjects were visually stimulated with 5.45, 8.57, 12 or 15 Hz. This well-known technique (steady state visual evoked potential) should elicit EEG peaks ...
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1 answer
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What's the correct way to align two signals downsampled at 10 Hz?

I'm trying to build a dataset where one of the features is a signal which has originally been sampled at 500 Hz, while another feature is a signal which was sampled at 100 Hz. I want to downsample ...
4 votes
1 answer
838 views

Appropriate Gaussian filter parameters when resizing image

When scaling an image down it is common to first convolve the image with a Gaussian filter. Given a scale factor $0 < s < 1,$ what is an appropriate $\sigma$ to use? For example, if $s = 0.5$ (...
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1 vote
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Downsampling( decimation) theory: additional frequency

I work on a simulation decimation filter: downsampling + filter. My test environment: low data rate receiver, BPSK, square root raised cosine filter with cutoff frequency =0.5, transition bandwidth = ...
1 vote
3 answers
193 views

Is there any deterministic downsampling algorithm for audio?

I was trying to use the scipy.decimate function provided in the library, but I had a question - I want a pre-processing algorithm to downsample audio in such a way ...
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In repeated upsampleing and downsampling by 2, how do i calculate the output Y(z)?

For example, if X(z) -> {downsampled by 2} -> {upsampled by 2} -> Y(z) Given that: X(z) = 1+z^2+z^12+z^19 How do I compute the value of Y(z)?
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243 views

Rate transition block in simulink

My model is operating at a sampling interval of $\frac{1}{f_0 \times N \times L_{maf}}$ s, (using a fixed point iterative method), now i want the output of my model to be at a sampling rate of $ f_0 \...
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Image downscaling methods

I am researching downscaling methods for image downscaling. I've both read and found area-averaging to work well in Python using CV2, but the settings in MATLAB allow for it's bicubic interpolation ...
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Dynamic sampling of thermal images

My master’s dissertation subject is to analyze and implement an algorithm that would sample (store) thermal images from camera with different frequency rates to optimize database size and processing ...
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240 views

how to find the frequency of the downsampled signal?

So, I am trying to solve this question. Consider the signal, $$x=\cos\left(\left(\dfrac{2\pi}{3} \right)n\right)$$ The signal is downsampled by a factor of two. Indicate the frequency of the resulting ...
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Does the convergence rate never increase of a Stationary Ergodic Random Processes under downsampling?

Summarize the problem Given A Stationary Random Processes (strict sense) $X_i$ I define two Stationary Ergodic Random Processes by $$ \bar{X}_n = \frac{1}{n} \sum_{i=0}^{n-1} X_i \ \ \text{and} \ \ \...
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1 answer
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How is non-integer upres downres (1080p game on a 1440p screen etc) calculated

Please redirect me if this is not the right place to ask. I was unable to find a straightforward answer to this question. What I am wondering is, if I am playing a 1080p game on a 1440p display, what ...
0 votes
1 answer
39 views

Duration of downsampled signal in analog frequency axis

Suppose, I sampled a signal, $x(t)$ and let $x[n]$ be the sampled signal of $x(t)$. Let then I downsampled $x[n]$ by a factor of $M=3$. Let $x[n]$ after being downsampled by the factor of $M=3$ yields ...
1 vote
2 answers
2k views

How to apply an anti-aliasing filter before downsampling

I have an eeg signal with two channels (f3m2 and f4m1) which is divided into epochs. I want to augment the data by taking every 5th sample. I can re-use the discarded samples to create 5 versions of ...
0 votes
1 answer
625 views

What should be IQ sample rate at least?

As i read, IQ sample doesn't need nyquist criteria. What is the mathematical representation of this result? Why IQ sample doesn't need nyquist frequency? I know that can be set to nyquist frequency ...
1 vote
1 answer
92 views

Increasing ADC output accuracy

Say we have a 12-bit ADC with 30 MHz sampling frequency. I want to perform several DSP operations on output digital signal so that resulting signal would have increased accuracy to 14 bits and output ...
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2 votes
1 answer
138 views

Is spectral density conserved after aliasing?

Will the integral of the PSD of a down-sampled signal still equal the variance in all cases
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1 answer
699 views

Python: Resample without equal

I would like to resample (downsample) a signal using python in order to get an even spacing and fill gaps. About the signal: It consists of a vector for y (amplitude) and x (timestamps) Very slow; $...
10 votes
1 answer
798 views

The Proper Way to Do Sinc Downsampling (DFT Downsampling) for Uniformly Sampled Discrete Signals with Finite Number of Samples

Given a discrete signal $ \left\{ x [ 0 ], x [ 1 ], \ldots, x [ N - 1 ] \right\} $ what would be the correct way to downsample it in the frequency domain (Sinc interpolation)?
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Perfect reconstruction in two-channel filter bank

[from Discrete-time Signal Processing by Oppenheim and Schafer, 3rd ed.] I was not able to prove this: If the analysis and synthesis filters are ideal so that they exactly split the band 0 ≤ |ω| ≤ π ...
1 vote
1 answer
194 views

Downsampling after a highpass filter

Question: The following sentence is not clear to me (especially why down-shift occurs). Could someone explain it please? On the other hand, downsampling the output of the highpass filter down-shifts ...
1 vote
2 answers
119 views

Book suggestion for upsampling and downsampling

I want to ask for a good textbook or online material which explains in detail: -the time and frequency domain mathematics behind upsampling and downsampling. -easy to follow Note: Oppenheim's ...
1 vote
1 answer
140 views

Remove noise introduced while converting a Delta-Sigma Modulated (DSM) signal into a pulse-code modulated (PCM) signal?

I'm writing a tool that converts a dsdiff audio file (dsd64) into a flac audio file (DSM -> PCM). The project is both a programming exercise and a signal processing exercise; I'm learning a lot ...
0 votes
1 answer
148 views

How to reprocess SDR data to be equal to that captured with a higher RBW

I have a data set that consists of max hold frequency vs intensity data from an SDR at a specific RBW. I want to reprocess the data as if I sampled it with the larger resolution bandwidth so I can ...
0 votes
1 answer
553 views

Apply filter before or after Downsampling?

Context: I'm trying to do formant estimation. My first attempt didn't work out all that well so I'm trying to follow closely Praat since their formant estimation is remarkably accurate. Question: I ...
1 vote
3 answers
670 views

Downsampling vs. ADC with lower Sample-Rate

I would like to know in general where the advantages and disadvantages are: Downsampling of a high sampled continuous analog signal in FPGA or µC and Direct use of a lower sampling rate, i.e. using ...
1 vote
1 answer
246 views

number of multiplications per second required by the system

Consider a system implementing a rational sampling rate change by 5/7: for this, we cascade upsampler by 5, a lowpass filter with cutoff frequency π/7 and a downsampler by 7. The lowpass filter is a ...
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1 answer
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Can you downsample unevenly with even distribution?

Could I downsample a series of length 10 to length 7, with even distribution? i.e. Numbers get split across two (neighbouring) resultant numbers, as opposed to one result being a combination of 1 ...
0 votes
0 answers
550 views

the number of multiplications per second required by the system

Q1. Consider a system implementing a rational sampling rate change by 5/7: for this, we cascade upsampler by 5, a lowpass filter with cutoff frequency π/7 and a downsampler by 7. The lowpass filter is ...
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0 votes
1 answer
128 views

The impact on the frequency of adding zero samples and non zero samples

Can someone give me a brief explanation of what is going on in here? I struggle to understand the full differences between the impact on the frequency of added zero samples and adding samples which ...
2 votes
1 answer
741 views

Downsampling and low pass filtering in one step?

Image pyramids are created by applying a lowpass filter (Gaussian) and then decimating the image (keeping only every n'th sample). In The Pyramid as a Structure for Efficient Computation the start ...
-1 votes
1 answer
201 views

How do I generate a smaller DFT result?

I have a very large input that I'm Fourier-transforming. Currently, I transform the entire signal and then downsample the result. Although the transform of the large input is expensive, my results ...
1 vote
1 answer
115 views

DTFT and a Downsampled Sinc Function

I found the answers to this question and this question to be extremely helpful in understanding the derivation of the downsampling or decimation property of the DTFT. Thank you! I am now struggling ...

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