Questions tagged [downsampling]
In signal processing, downsampling (or "subsampling") is the process of reducing the sampling rate of a signal.
0
votes
1answer
26 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 ...
0
votes
1answer
17 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 ...
2
votes
1answer
39 views
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 ...
0
votes
0answers
32 views
How to calculate the variance of noise when an image is downsampled?
I have a noisy image for which I know the noise variance. (Basically I created noisy image by adding noise). Now, I'm downsampling this noisy image. How does the noise variance change? Is it possible ...
1
vote
1answer
29 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 ...
1
vote
0answers
24 views
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 ...
1
vote
0answers
45 views
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, ...
0
votes
1answer
65 views
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 ...
3
votes
1answer
341 views
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, ...
0
votes
1answer
107 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 ...
6
votes
2answers
1k views
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 ...
0
votes
2answers
105 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 ...
0
votes
1answer
131 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 ...
1
vote
1answer
225 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 ...
4
votes
2answers
265 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.
...
2
votes
2answers
60 views
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 ...
2
votes
0answers
50 views
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 Ts.How can I sample the continuous signal by Ts/2 instead of Ts in order to get two ...
0
votes
3answers
140 views
Are oversampling and downsampling the same thing?
According the books I have on DSP,
is oversampling, sampling a signal at a much higher samplingrate then normally required, so to reduce the sample-rate (and increase the resolution of the signal) ...
0
votes
0answers
43 views
Can we sample the signal with any period as long as the Nyquist rate is respected
I have a question regarding the sampling rate. Suppose that we transmitted a signal $m(t)$ then at receiver side, we received the continuous signal $x(t)$, which is time varying and sampled with a ...
2
votes
2answers
139 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 sent $150\text{ ms}$ long TTL pulses to a computer recording the voltage data, at the same time as to an LED in the field of view ...
2
votes
3answers
147 views
Decreasing Sample Rate in DFT (FFT) for Audio Analysis
I'm working with audio data analysis through FFT algorithm.
My example audio is a sine wave at 440 Hz and 44100 Hz sampling rate.
FFT methods in programming, like ...
0
votes
2answers
273 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 ...
0
votes
1answer
117 views
Downsampling in MATLAB - why scaling filter coefficients?
Trying to undertsand how MATLAB does resampling, looking at toolbox/signal/resample.m.
This is the part where (downsampling) filter coefficients are calculated:
<...
0
votes
1answer
48 views
Most natural interpolation to simulate increasing distance?
Background: I'm generating multiple datasets with varying scales of resolution to simulate taking pictures from varying distances and then comparing image classification performances. For example ...
0
votes
1answer
556 views
Downsampling audio for use in Machine Learning
I'm trying to use the work (Neural Networks) done in this repo:
https://github.com/jtkim-kaist/VAD
It says this:
Note: To apply this toolkit to other speech data, the speech data
should be ...
0
votes
0answers
125 views
Downsampling using Matlab functions suited to embedded applications
Not looking for long or detailed responses, but something to send me down the right track. Links, application notes, book chapters, etc..
What I want:
Looking to use upfirdn() Maltab function to ...
0
votes
1answer
67 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) ...
3
votes
2answers
280 views
What is the effect of the natural logarithm in the frequency domain?
I have read that taking the natural logarithm of a signal $x$ in the time domain will introduce a spectral broadening and hence "up-sampling" process before the logarithm is required. I tried to test ...
1
vote
1answer
179 views
Downsampling a high pass filter
If I have an ideal high pass filter as the one in the picture:
And I downsample it by 2, e.g. $h_{new}[n] = h[2n]$, is my understanding correct that the resulting filter would look like this in the ...
4
votes
1answer
2k views
Python's $\tt resample$ vs $\tt resample\_poly$ vs $\tt decimate$
I have multiple signals each measured with a sampling rate 300Hz. They are mostly periodic, although there are some parts of some of the signals, that seem to be random and do not follow the rest of ...
1
vote
2answers
56 views
Explaining a statement regarding aliasing in a document
I am reading this document and in the section "Aliasing and Anti-Aliasing", the author make the following statement:
Consider a signal with two frequency components: $f_1 = 10\,\text{Hz}$ which is
...
3
votes
0answers
4k views
Downsampling and upsampling of a signal in Python
If I want to downsample a signal in Python, is it better to use method resample from SciPy Signal Processing module or method decimate from the same module? What is the difference between these two ...
0
votes
1answer
33 views
How left out down-sampling in 3D-DWT just on the Z direction
I am working on image processing by a 3D wavelet transform.
I have a problem with the classification size of the wavelet coefficients. As you know, when we apply 3D_DWT on the image (for example: ...
1
vote
1answer
325 views
Image zoom out using Gaussian blur and downsampling
I am trying to implement a simple zoom out algorithm using two steps:
The image is blurred using gaussian convolution of standard deviation $0.8\sqrt{{\tt zoomfactor}^2-1}$ as we saw in class.
The ...
-1
votes
1answer
56 views
How does the bandlimit of an image reduce 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 ...
3
votes
1answer
499 views
Downsampling and convolution
(Code snippet with example below).
In MATLAB, assume I have a long signal vector y (length N) that I wish to convolve with a ...
0
votes
0answers
43 views
Accomodating different sample rates in DTMF decoder: resampling vs dynamic algorithm
I'm trying to write a real-time DTMF decoder, but it needs to handle multiple sample rates depending on the input audio source. What's the typical method for dealing with this? Should I simply ...
2
votes
1answer
692 views
Down sample incoming stream of data to plot a dynamic graph
I am working on a module where I need to plot ECG streaming data on a graph. This graph has configurable speed i.e. plot 1 heartbeat data sample within say 50mm,25mm, etc. For this, I am required to ...
3
votes
0answers
431 views
Synchronizing signals with different sample rates
I am relatively new to signal processing, so I am still missing some basic knowledge, but I am trying to improve as much as I can. I am trying to synchronize two signals with matlab using cross-...
1
vote
1answer
736 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 ...
3
votes
1answer
234 views
Is FIR decimation the fastest possible method for integer downsampling?
For a digital music synthesizer I am developing, I have a stream of incoming samples $x_i$ and would like to downsample by $M$ to obtain a stream of samples $y_{Mi}$. I am currently bandpassing the ...
3
votes
1answer
869 views
Downsampling in Matlab simple example
I'm trying to visualise downsampling in the frequency domain in matlab
I take a simple sinusoid, perform an fft and plot a two sided spectrum. Then I downsample the time domain signal (...
0
votes
1answer
397 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:
$...
0
votes
1answer
151 views
Downsampling by non-integer factor Filter requirement [duplicate]
I am trying to implement a logic to downsample data in non-integer factor.Lets say,converting 48Ksps to 1344 samples per second.Have two step implementation of upsample by K ,and downsample by L is in ...
1
vote
0answers
795 views
Decimation function implemented in standard C [closed]
I'm thinking in a decimation C function. The prototype of the function is:
decimate(int N, float input[], float r, float output[])
where N is the length of array ...
7
votes
2answers
212 views
Is this signal perfect reconstructable?
The question is as follow:
Let me do the analysis:
The downroad first:
\begin{align}
X_1(z) &= z^{-1}X(z)\\
X_2(z) &= \frac{1}{2}\left\{X_1\left(z^\frac{1}{2}\right)+X_1\left(-z^\frac{1}{2}\...
5
votes
1answer
435 views
Shannon interpolation formula for downsampled data with an “almost ideal” low pass filter
Let $x[n]$ be a discrete time signal with DFT given by $X(f)=\sum_n x[n]e^{-2\pi inf}$ supported on $[-1/2M,1/2M]$ with $f\in[-1/2,1/2]$.
I can then down-sample to get $y[n]:=x[nM]$. Then, let
$$\...
4
votes
2answers
1k views
Understanding audio downsampling code (JavaScript) and adapting to a different ratio
I inherited responsibility for some audio downsampling code that I don't fully understand:
...
0
votes
1answer
260 views
what is difference between Alias vs. down sampling? [closed]
could someone help me explain downsampling in the context of Nyquist–Shannon sampling theorem and tell the difference between Aliasing and downsampling.Also is downsampling and undersampling the same ?...
0
votes
1answer
142 views
upsampling and downsampling operator
I am trying to prove that for all $x,y \in l^{2}(\mathbb{R})$, it holds that $$\left\langle\left(\downarrow M\right)\left[x\right],y \right\rangle = \left\langle x,\left(\uparrow M\right)\left[y\right]...
