Questions tagged [downsampling]
In signal processing, downsampling (or "subsampling") is the process of reducing the sampling rate of a signal.
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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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1answer
64 views
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 = ...
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3answers
72 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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23 views
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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48 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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32 views
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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31 views
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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1answer
59 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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16 views
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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1answer
46 views
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 ...
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1answer
14 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 ...
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2answers
270 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
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1answer
72 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 ...
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1answer
47 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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1answer
120 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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1answer
83 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; $...
3
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1answer
334 views
The Proper Way to Do Sinc Downsampling (DFT Downsampling) for Uniformly Sampled Discrete Signals with Finite Number of Samples
Given a signal $ \left\{ x [ 0 ], x [ 1 ], ..., x [ N - 1 ] \right\} $ what would be the correct way to downsample it in the frequency domain (Sinc interpolation)?
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38 views
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
...
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1answer
55 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 ...
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2answers
65 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
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1answer
51 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 ...
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1answer
67 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
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1answer
100 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 ...
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3answers
258 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 ...
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1answer
172 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 ...
0
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1answer
41 views
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 ...
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0answers
410 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 ...
0
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1answer
76 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 ...
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0answers
39 views
Adding zeroes in between the samples of a discrete frequency domain leads to both zero padding and scaling
I won’t show ALL the calculations, but I’ll describe the problem fairly enough to understand.
We’ve been taught that upsampling on one domain leads to padding zeroes or added time period which is zero ...
2
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1answer
287 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 ...
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1answer
133 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 ...
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1answer
57 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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2answers
898 views
Decimation Question about using a low pass filter before downsampling
I have a bunch of audio files that have a sample rate of 380kHz, however I would like to reduce this sampling rate to 44.1kHz. From doing some research online, it seems like I will have to use a low ...
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1answer
34 views
Understanding index transformation in derivation of Fourier transform for sampling rate reduction
Was going over some notes regarding deriving fourier transform equation for Sampling Rate Reduction. Reference to Notes from below link https://ocw.mit.edu/courses/electrical-engineering-and-computer-...
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1answer
90 views
Oversampling a signal
I’ve built a circuit with an analogue sensor (70 Hz bandwidth) connected to a 24 bit ADC, which is oversampling the signal at 10 kHz. Nyquist sampling theorem implies I should sample by at least 140 ...
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2answers
56 views
How mic setting will affect audio classification model?
I have audio samples with three classes :
100 audio samples : class 'A'
100 audio samples : class 'B'
100 audio samples : class 'C'
...
0
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1answer
53 views
Downsampling - how many extra samples to include
I want to downsample a finite section of an equidistant time-series
$$x_i, \qquad i=0\dots n-1$$
by doing an FFT and dropping the upper part of the spectrum. Since the FFT looks at $x_i$ as a cyclic ...
0
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3answers
83 views
Loosing information in decimation - without aliasing
We sample each other sample (01010101). Now say we have a signal - that is inside the original sample which has the pattern of (010-1).
Decimation gives us 000 for this sub-signal.
How to prove this ...
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2answers
49 views
Relationship between sampling and number of pixels?
In case of digital images, what is the relationship between sampling and number of pixels? For upsampling, the number of pixels increass, and for down sampling, the number of pixels decrease??
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How do you change an instance of dsp.DigitalDownConverter object in MATLAB to work with filters other than the ones it is originally defined with?
If you look at this website:
https://www.mathworks.com/help/dsp/ref/dsp.digitaldownconverter-system-object.html
you will see an example (with code) that attempts to up convert and down convert a ...
0
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3answers
217 views
How and why does downsampling reduces resolution in time
in my Course we talked about filter banks and the prof said that we get reduced resolution in time because of the downsampling after the band-pass filters. Is this because we now have fewer sample ...
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2answers
187 views
Downsampling issues
I have this data that need to be downsampled so that it can be fed into a classifier. The issue is that I need to downsample from 1000Hz into 20Hz. If you see the graph below, the blue line is the ...
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1answer
115 views
How is downsampling and low-pass filtering done in MS-SSIM?
I am just studying the Multiscale Strutural Similarity measure for image quality and going through the original paper [1].
I think I understood the basic ides and "regular" structural similarity, but ...
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3answers
159 views
Can Carrier Offset cause Image Problems
The main reason why we use the Direct conversion receiver with zero IF is that we don't have to deal with the problem of images. For achieving zero IF we need to ensure that the receiver Local ...
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1answer
196 views
2D Fourier downsampling
How can one correctly downsample a Fourier 2D matrix of complex numbers ? More precisely, if I have a 2D DFT of an image:
x=phantom
X=fft2(x)
How should I do to ...
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2answers
59 views
How do wavelet levels depend on one another?
I am working with wavelets for my thesis, and I would like to know if there is an intuitive dependency between the levels of a DWT.
To make it clear: The DWT performs a convolution, and then the ...
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1answer
126 views
How should I downsample my sensor?
I have 2 sensors, sensor A is sampling a signal at 1kHz, and sensor B is sampling the a signal at 100Hz.
Every timestamp that sensor B takes a measurement at is contained in sensor A. That is, ...
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1answer
40 views
std::cosf fluctuation: Results are off in low frequencies [closed]
I attempted to generate a continuous wave signal by using the C++ cos/sin functions. It's partly successful, meaning high frequencies seems ok, but very low frequencies give unexpected results. The ...
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1answer
163 views
Decimation with IIR filter altering amplitude of signal
I'm downsampling a signal through decimate (scipy implementation), but the result has a different amplitude than the original signal, which if I understood correctly, shouldn't happen. The original ...
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1answer
147 views
Confused about filter's cutoff frequency in rational sampling rate converter
A interpolator which increase sampling rate by L times is followed by an anti-imaging filter, the filter is said to have a cutoff frequency of Fs/2L. Is Fs here is the frequency before or after ...
