# Questions tagged [downsampling]

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

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### What is the best method of describing the effects of downsampling on a chromatographic signal?

I am in the process of compressing a set of chromatograms to develop a preprocessing pipeline, that will end with DTW for peak alignment. During this process I have downsampled a signal from 0.4 ...
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Consider a discrete-time sequence, $y[n]$, defined as: $$y[n] = \frac 12 x[n] + \frac 12 (-1)^n\: x[n]$$ where $x[n]$ is another discrete-time sequence. The DTFT of $y[n]$ defined as $Y(e^{j\omega}) = ... 0 votes 1 answer 66 views ### Lowpass filter to downsample data I have some data that is sampled at a certain rate (16384Hz). I am only interested in the 10-30Hz region, so I want to downsample the data. My idea to do this goes as follows: I apply some kind of ... 1 vote 1 answer 150 views ### How does downsampling decrease the noise power? I read one equation from a technical document, i.e., assuming the time-domain white Gaussian noise samples with variance$\sigma_{TD}^{2}$in dB are sampled using ADC with sampling rate$f_{s}^{ADC}$, ... 0 votes 1 answer 39 views ### Does SDR configured with low sample rate automatically averages samples? This is probably a basic question but I didn't find any answer online. Suppose we configure a SDR (least say, with a maximum sample rate of 100 Msamples/s) with a low sample rate (e.g. 1 Msample/s). ... 0 votes 1 answer 175 views ### How to calculate phase rotation of I/Q reference samples for Bluetooth Angle of Arrival I am trying to compensate phase rotation due to carrier frequency offset (CFO) for Bluetooth Low energy (BLE) Angle of Arrival (AoA). In BLE AoA the adv. packets carry a Constante tone extension @... 2 votes 2 answers 107 views ### Is downsampling LTI for bandlimited inputs? This question stems from the discussion we had on a previous question of mine. The point of contention is whether the downsampling operator is time invariant or not. Which gives us a new condition to ... 0 votes 1 answer 176 views ### Is the following system LTI and what is its purpose? Above is a block diagram of a discrete-time system$T\{x[n]\} = y[n]$. Here,$h[n]$is the impulse response of an arbitrary LTI system. Firstly, is this overall system LTI? I don't think so because ... 0 votes 1 answer 53 views ### Can we do down sampling by taking fft, omitting samples on the ends of the spectrum, and then taking inverse fft? Suppose that we have a signal with a length of 4096 and want to down sample it by a factor of 2 and obtain a signal with a length of 2048. Suppose that the the maximum frequency content of the signal ... 0 votes 0 answers 125 views ### Is this how to show decimation in the frequency domain? Let's say I have a discrete-time signal$y[n]$that is passed through an Ideal Lowpass Filter (impulse response$h[n]$) to get$y_1[n]$. The filter has cutoff frequencies at$\pm \pi/N$rad. Now this$... 1 vote
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### Summarization of audio in frequency domain?

I need to summarize a set of samples representing an audio to achieve a smooth zoom animation for a spectrogram in my app. In the time domain (waveform) I achieve this by resummarizing the samples ...
507 views

### How is the DFT involved in downsampling?

I recently had my first proper class of DSP and upon completing the review of Signals and Systems my professor started working on the concepts of upsampling and downsampling. Of course as is their ...
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### Effect of FIR filter on the time resolution of the signal

Let's say I have a noisy raw signal with 1GS/s sampling rate (That means the time resolution is 1 ns). Now I apply a FIR lowpass filter (window filter) of 25 MHz on it. The length of Window filter ...
1 vote
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### Frequency constraints on a down-sampled signal

I am preparing for an examination and am confused about one of the questions on the study guide. The question given on the study guide is given below. We want to implement a change of sampling rate ...
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### Observed Maximum Frequency Not Expected For Given Sample Rate

I'm downsampling a given .wav from 44100 to 22050 samples/second. When I play it back I'm looking at the signal with an EQ, and I would expect that I wouldn't see any content above ~11k. However, I ...
1 vote
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### Symmetric half band filter - redundant oversampling?

I'm making a basic symmetric decimating half band filter (M=2), with alternating 0 coefficients. The signal is oversampled by a factor of 2, at frequency $f$. I must be missing something simple, but ...
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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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### 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? ...
151 views

### 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 ...
608 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 : 2D Fourier downsampling some time ago that talked about my own doubt, that is to ...
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### 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 ...
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### 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 ...
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### 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
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### 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'...
84 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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### 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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### 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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### 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 ...
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### 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 ...
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### 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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### 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 ...
1 vote
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### 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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### 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 ...
2k 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 $s = 0.5$ (...
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 = ...
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### 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 ...