Questions tagged [downsampling]

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

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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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30 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' ...
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50 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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30 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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83 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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3answers
310 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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39 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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22 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 ...
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1answer
56 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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743 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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39 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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164 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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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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Bandpass filter is not working as expected

The sampling rate that I have currently is at 384kHz and I want to downsample it down to 44.1kHz. I want to use a bandpass from 5kHz to 200kHz but I am only able to bandpass up to 192kHz for some ...
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34 views

Can largest-triangle-three-buckets downsampling method used with fourier transformed signal?

I've been reading on the largest-triangle-three-buckets downsampling method for downsampling. Though it was originally published in the thesis "Downsampling Time Series for Visual Representation&...
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2k 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
28 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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530 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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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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9 views

How to choose the appropriate number of samples for discrete wavelet transform denoising?

I want to make sure I am understanding the filter bank frequencies correctly in DWT decomposition. If my sampling frequency is 30kHz, then would I need to input data with 30k samples which later will ...
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212 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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30 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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231 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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1answer
39 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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1answer
36 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 ...
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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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3answers
41 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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40 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 ...
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1answer
109 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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3answers
43 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
53 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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120 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
36 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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2k 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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2answers
86 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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2answers
3k views

Trying to down-sample 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 ...
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How can I extract the 2 polyphase components of a signal after sampling at the half of sampling rate

Suppose I have a continuous signal $x(t)$, which was sampled using sampling function $s(t)$ whose sampling rate is $T_s$.How can I sample the continuous signal by Ts/2 instead of Ts in order to get ...
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1answer
43 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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78 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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111 views

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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1answer
743 views

Downsampling and Convolution: When Can one Swap Between Them?

(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
36 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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2answers
406 views

How can I synchronize signal from an LED and TTL pulses better?

I would like to synchronize my video and voltage data using Python. (I obtain these data using Bonsai and Open Ephys for an open field exploration experiment.) I sent $150\text{ ms}$ long TTL pulses ...
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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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1answer
91 views

How Is the Bandwidth of an Image Reduced 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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70 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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76 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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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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1k 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 ...