Questions tagged [downsampling]

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

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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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30 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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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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35 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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Pandas resample.mean()

I have a question to all you filter experts out there. I have some engine data sampling irregularly at about 50Hz. Recently I've been downsampling via the Pandas resample().mean() method. Basically ...
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39 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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39 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 ...
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54 views

ADC sampling rate implications Matlab/Simulink M-PSK modulation

I am trying to find a way to evaluate what would be the minimum sampling rate used in a modulated waveform using matlab / Simulink. The real scenario would be let say a M-PSK waveform of Y bandwidth ...
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How to improve interpolation for chroma upsampling (4:2:0 to 4:4:4)?

I am trying to perform the best possible interpolation in order to perform proper chroma upsampling from 4:2:0 YCbCr to 4:4:4 YCbCr. I have implemented the improved interpolation proposed at this ...
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What is the right way to downsample using Fourier method?

I want to know what is the right way to downsample a sampled signal using Fourier transform as the implementation in scipy.signal.resample confuses me. Reading ...
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261 views

What is the impulse response used in an interpolation filter when upsampling?

I need to downsample a single period waveform from $M$ samples to $L$ samples. If that matters, in my particular case, $L=M-1$. I read about downsampling and came to the conclusion I need: expand ...
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Nyquist sampling theorem / Nyquist - Shannon theorem evaluation over M-PSK

I am trying to simulate an M-PSK Tx-Rx System on Simulink and analyse what the effect of sampling rate reduction would have on it. More, particular I am trying to prove what Nyquist sampling theorem ...
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How to Downsample The Chrominance Components

So I am doing an image compression project for college and am trying to create a visual demonstration of how downsampling chrominance components can reduce the amount of digital information while ...
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356 views

downsample signal to a specific number of samples in Python

The Python Scipy library provides several functions to downsample signals, but they all have limitations: The resample function is based on Fourier method, which means it assumes periodic signals. ...
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189 views

Downsample: resample vs antialias fitlering + decimation

I have a discrete signal sampled @Fs. I need to downsample it to Fs/k. Main reason is to reduce signal bandwidth and speed up computation : I'm only interested in a reduced bandwidth < Fs/2k. Some ...
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1answer
59 views

Improving spectral response with lost downsampled data

I have a project that is resource constrained and must maintain a specific FFT length and small FFT bin width, down at baseband. My sampling rate is very high and needs to be downsampled to anywhere ...
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How to downsample my data readings from 0.5hz to 0.001667hz. Do I filter and downsample?

I have a device that, in the lab, takes voltage readings every 2 seconds. However in real-life application the device would only wake every 10 minutes and then take a 100 readings whilst awake. How do ...
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Clarification regarding discrete wavelet transform

One of the books on "Conceptual Wavelets" by Fugal explains some major differences between the undecimated discrete wavelet transform (UDWT) vs. discrete wavelet transform (DWT). In UDWT the scale of ...
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Analog-to-Information Converters?

In Analog-to-Digital Converters(ADC), the signal is first sampled at a rate higher than or equal to the Nyquist, then quantized and encoded. In Analog-to-Informations (AIC), the sampling and ...
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FFT of white noise with different sampling rate

I have a question on how I should interpret the white noise power level (noise floor) obtain from FFT for different hardware sampling rates. I realized if I sample the same noise at different rates (...
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Bandpass Experiment: Weird graph! amplitude mismatch?

Why is this generic BP filter seem to magnifying amplitudes when I run it at lower sample rates? The bass range seems to 32 times louder at 1275 Hz (44.1 kHz / 32) than at 44.1kHz? Here is a graph of ...
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65 views

RSP1A sample rate vs if bandwidth

I'm using the RSP1A SDR and I want to understand how to choose the best configuration for receiving a signal of 125 khz bandwidth. I would like to know if when choosing the option 200 KHz IF ...
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1answer
136 views

How to prevent distortion after down-sampling?

I am new to audio signal processing, but in one of my machine learning projects that I am working on, I need to down-sample my audio somewhere in the middle of my neural network. Therefore, I need a ...
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84 views

Better understanding of downsampling (decimation) and upsampling (interpolation)

Although some questions were asked about this topic, I have not seen any that answers all the basic questions, that is why I took the liberty to ask more about this. I suggest to limit, (or at lest ...
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31 views

Polyphase components Spectrum formula in Discrete time

I am trying to understand the meaning behind some of the components of the formula for polyphase components in discrete time. Note that $\Omega$ indicates discrete in this notation and the formula is ...
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49 views

How to sketch this multirate system spectrum?

In the following system: The signal x(n) is upsampled by 2 and then filtered. The signal and the filter have the following spectrum: After upsampling the spectrum of X would look the same except ...
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72 views

Image downsampling with Haar DWT?

How can the resolution of an image in matlab be reduced by using 2D haar wavelet by downsampling-decimation? Is there any predefined code or tool within wavemenu? thanks in advance
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314 views

Why does downsampling stretch a signals frequency response and upsampling shrink and create images of a signals frequency response?

I am learning some basic DSP and I have a pretty good intuition as to why sampling creates spectral images of the frequency response at intervals of the sampling frequency (convolution with pulse ...
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564 views

Synchronization and downsampling after matched filtering - GNURadio polyphase clock sync

I am trying to model a QPSK transmission. For this, I am using the software GnuRadio and more specifically the block polyphase clock sync. This block performs timing synchronization for PAM signals by ...
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75 views

ADC way faster than microcontroller

I am getting into signal processing, and am working on a project. My analog-to-digital converter has a sample rate of 10 kHz, whereas my microcontroller can only handle up to 3 kHz. What does that ...
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63 views

Filter design for decimation of 1.1 kHz sensor sample rate to 100 Hz processing rate

Suppose, you have a signal source which is sampled by 1100 Hz and is "somehow" band limited to either 235 or 440 Hz. In my application, that's the ST IIS3DHHC accelerometer. There is an appnote for ...
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268 views

Decimation vs Mean in downsampling operation

Let's suppose I have a discrete signal $x[n]$ with a certain frequency $f_x$. Now, due to various unimportant reason, I want to obtain a new signal $y[m]$ with a new frequency $f_y = \frac{f_x}{k}$, ...
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132 views

Aliasing from downsampling and Nyquist

In a book Conceptual Wavelets in Digital Signal Processing by Lee Fugal 2009 on page 246 the author talks about aliasing present in DWT subbands due to downsampling by 2 and states: Recall from DSP ...
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169 views

Upsampling and downsampling signals as a preprocessing step for a neural network

I have audio data acquired from a 4 channels sensors array. As a preprocessing step for a neural network, I want to beamform and focus on the sound source. For higher resolution in the beamforming ...
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109 views

Why do I have to scale filter coefficients during bandlimited sample rate conversion?

I am writing an example for how to perform sample rate conversion using windowed sinc and polyphase filters. Here is the C++ code as a github gist. So far, this works, and I think I have understood ...
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156 views

Down sampling an EEG signal

I have a set of 10 minute EEG signals that were sampled at 400 Hz and have 16 channels which corresponds to a 16x240000 matrix. These EEG signals belong to two different classes. I am trying to ...
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1answer
44 views

Differences in moving window rms due to sampling rate

I have a 10 second recorded signal band pass filtered from 100-500 Hz. The original sampling rate is 10 kS. Now I run a moving window RMS with a window length: 10 ms on the signal (10/1000 * sampling ...
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Understanding sampling rate conversion

I am a little bit confused about the concept of sampling rate conversion. Consider the following question: Wideband telephony signals are sampled at a sampling frequency fS1 = 16kHz. To process these ...
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2answers
68 views

Reversing the order of up and downsampling

When we are dealing with the problem of changing the sampling rate by a noninteger factor like L/M, we first need to the do the upsampling, and then the downsampling. My question is that under which ...
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Why is my resampled signal cutoff when resampling with a windowed FIR filter in MATLAB?

I have an exercise to write a function which upsamples or downsamples a signal by a factor of F (integer) using a FIR filter windowed with a Kaiser window function. Exercise I had last week included ...
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What are the differences between Gaussian down-sampling and bicubic down-sampling in Matlab? Which is more accurate for simulating low resolution?

I see in some of the technical papers, good practice for downsampling is to first pass the image through a Gaussian Filter and then take sampling to avoid problems like aliasing and so on. However, ...
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Follow up question regarding: “Complex sampling can break Nyquist?”

I'm having some trouble understanding the sample rate limitations when considering a complex baseband signal. I understand (based on the linked SE questions below), the either (1) physically ...
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Scipy resample, “fourier method” explanation

I am seeking explanation of what "Fourier method" is that is described for resampling in documentation of resample() method. I want to downsample an array. I know what decimation is and how it works, ...
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256 views

How good or bad my downsampled data is?

Suppose I have time series data at a one-minute resolution. Now I downsample data by taking mean of every 10-minute window, i.e., after downsampling, 60 readings will reduce to 6 readings. How should ...
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Why should an image be blurred using a Gaussian Kernel before downsampling?

I recently read that before downsampling an image, it should be blurred using a Gaussian Kernel. This way, the downsampled image is better than just picking a single pixel out of a NxN block or ...
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251 views

How to determine the original size of the FFT used in unknown OFDM symbol

Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins. Down-sampling to 512,256,128,64,32 yields the following. Do not see how ...
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377 views

Convert 96 Khz to 48 Khz audio: is this simple downsampling method ok?

I have an audio signal x sampled at 96 Khz. I have already lowpassed it with a cutoff somewhere between 20 Khz and 22 Khz, so there should be nothing left of ...
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561 views

Downsampling impact on complex phase

For my application, I have to downsample a bandpass complex signal which spectrum is located on the second Nyquist zone. Knowing that this processing will cause a spectrum inversion, what would be ...
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890 views

Properties of Up- and Downsampling

Given a gaussian white noise with mean 0 and $\sigma = 1$. I'm interested in the PSD (power spectral density), when the signal is plain up- or downsampled. No interpolation, no filtering nothing. ...
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Level Correction For Digital Down-Convertion?

I am trying to understand a subtle (sorry if this is obvious) difference in the computed output power after a DDC process. Here is the story: Suppose I generated a 10 MHz signal from a microwave ...