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

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Quadrature subsampling result not as expected

Let's suppose I have an ADC running at 81.824MHz. I am quadrature subsampling a signal that is at 143.5MHz using a sampling rate of 81.824MHz/4 = 20.456MHz = Fs. I expect the signal to appear at ...
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47 views

up down sampling and low-pass filters

I am trying to figure out what seems very trivial thing about down sampling and up sampling. The problem that I am facing is how to find the effects of up sample on a signal followed by a filter ...
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42 views

down sampling and a factor of 2 without loss of information

I am trying to understand the limits of down sampling on a signal, i.e. how far can I go without loss of information or overlapping. It says in the solution manual of the Oppenhiem and Schafer book ...
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47 views

Downsampling fft results to a graphics display

I'm new to dsp. I've got a complex signal that was sampled at 192kHz then an fft of 16384 bins created. This now needs to be plotted on a graph for a real time spectrum display. The problem is if ...
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57 views

Downsampling PCM Audio

I'm looking everywhere for solutions for audio downsampling. However for one reason or another they are incomplete, sometimes buggy, and sometimes are in a programming language I cannot understand. ...
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44 views

Is digital up and down sampling linear/causal/time-invariant?

So I am trying to determine whether the process of up sampling (zero padding) and downsampling are linear, causal and/or time-invariant. Based on some resources I found online, I am under the ...
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33 views

What is a correct way to downsample an impulse train

So I have a signal which is caused by an impulse train. I can determine the impulse train with 500hz but sample my output signal with only 10hz. Then I want to calculate an impulse response function. ...
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1answer
40 views

Perfect reconstruction ( Single Channel )

I was trying to solve the following problem . Given an input x[n], consider upsampling by 2, followed by interpolation with a filter having z-transform H(z) for magnification of the signal. ...
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1answer
26 views

Downsampling MP3 for FM broadcast

I have some MP3s that are encoded at 44.1kHz with a bitrate of 160kbps. I hook these up to my car using an FM transmitter and the sound quality isn't particularly great. Low and high notes sound ...
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4answers
77 views

up sample and down sample

Let's say that I have a sampled signal x[n], it is being, in this exact order, up sampled by 2, down sampled by4, up sampled by 4 and down sampled by 2 to produce y[n]. It seems to me that it should ...
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41 views

Image getting completely white on downsampling

I performed an image downsampling with averaging operation(The image is divided into 2 by 2 blocks,then it is downsampled by 4 times.New pixel values od downsampled image is replaced with the mean of ...
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3answers
80 views

Decimate/downsample a signal from 1920.93Hz to 1920Hz. Possible? [duplicate]

I've just learned that the A/D converter I am using is not sampling at my desired sampling rate. I request 20 seconds of data at 1920Hz and I receive 38400 points of data that were actually sampled ...
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116 views

Why need an low pass filter after up-sampling? [duplicate]

I understand why there need an low pass filter before down-sampling, the sample frequency need to be at least twice of the max frequency signal, else there will be ...
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101 views

Effects of sampling rate approaching the Nyquist frequency? (not undersampling)

I understand that you need to sample at a frequency greater than or equal to the Nyquist frequency to reconstruct a signal/aliasing etc. I read though that a "more conservative" approach is to sample ...
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2answers
253 views

Trying to understand downsampling and then upsampling

I am trying to understand how this works, specifically, what the DTFT of each step looks like in each step of the chain (for understanding). I am not looking for an answer like because the input ...
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3answers
122 views

How to display the output as the input with a fractional delay? [closed]

I am trying to introduce a fractional delay in my input vector x[n] so the output is something like y[n]=x[n-M/N]. I am not supposed to use the MATLAB fracdelay function.So, I used sampling and delay. ...
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7answers
662 views

Downsampling/Decimation - When is well done?

I am working on decimation of signal, and I want to know which is the best way to understand if the downsampling is well done or not. At the moment I am comparing the FFT of the source signal and the ...
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1answer
79 views

A question on filters

I am fairly new to DSP have been reading up on digital filters and have a few questions. I have a signal with very high frequencies whose DC component i want to estimate. The magnitudes of these ...
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1answer
120 views

Downsampling oversampled image (smallest size which retains image 'detail' within acceptable limits)

I have a large collection of oversampled images (family photos of varying 'sharpness' scanned at a uniformly high dpi) and would like to downsample them to optimise storage space whilst retaining ...
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2answers
73 views

Create an aliased image in FD

Is there an accurate way to create an aliased image from the Fourier transform of the original image? in other words, i have the Fourier coefficients of an image and i want to make down-sample in ...
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1answer
70 views

Downsampling a PSD that was generated by zero-padding - worth it?

Let us say we have a signal $y(k)$ that is of length $K$. I can compute its PSD, also of length $K$. Let us say that this length was not good for finding peaks, so I computed a PSD that was of length ...
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84 views

Reducing frequency of a signal

I have a signal that I want to make it sound like a whisper. This is probably better than using a voice conversion system, but I was just want to do some experimenting before. I was thinking maybe ...
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116 views

Direct IQ sampling symbol transition problem

In a direct sampling RF front-end, we can get real samples. But when we sample the signal with two ADC with a sampling delay $ \frac{4n+1}{4fc}$ where $n$ can be $0,1,2 \dots$ Then we have In phase(I) ...
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53 views

Preserving integral through downsampling

I've got a high-resolution image segmentation, which I'm downsampling (and non-linearly deforming) to fit on an ROI image. I typically blur the high-res image before downsampling with a Gaussian-fwhm ...
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0answers
149 views

Most efficient way to downsample a signal by a factor of 2.5x

I know that to downsample by a factor of 2.5x one can upsample a signal by a factor of 2 and downsample by a factor of 5. I am wondering what is the best and more efficient way of downsampling by a ...
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1answer
720 views

CIC Filter vs Simple Downsampler

I' trying to implement a QPSK modulation/demodulation. At one point I have to decimate my signal by 4 for an easier implementation. I've read everywhere that the best way to do it is to use a CIC ...
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2answers
718 views

Decimation of signal. How to plot frequency spectrum

I have an FDM signal from 0 to 70 MHz. The total signal contains 4 FDM signals from (0-fs/4), (fs/4-fs/2), (fs/2-3fs/4) & (3fs/4-fs). I used fvtool command in matlab to plot these signals. Then i ...
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2answers
1k views

Downsampling - upsampling FFTW

I'm having 2 signals which have different sampling rates i.e., 1ms(A) and 4ms(B) and I've tried to upsample/downsample either of the signals based on the code snippet Resampling based on FFT which I ...
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2answers
549 views

Oversampling then filtering and downsampling

Currently I'm working on a project to record ELF (Extremely Low Frequency) signals from a receiver. The highest frequency of interest is about 30 Hz and the system should have a flat frequency ...
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162 views

Downsampling and Gradient filtering

Are the following sequence of operations the same - Down-sampling filtering followed by gradient filtering with kernel [-1 0 1] Gradient filtering with kernel [-1 0 1] followed by down-sampling ...
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How can I resample a signal with an arbitrary factor (e.g. 128000Hz to 16000.1Hz) in Matlab?

I need to simulate the sampling of a continuous (fsCtu = 128000Hz), acoustic signal with two microphones that have a slight offset in sampling rate (fsMic1 = 16000, fsMic2 = 16000.1) in Matlab. What ...
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67 views

Sample keypoint found in multi-scale to one scale (scale space with O octaves)

For a multi-scale keypoints detector, local extremas are found between the scales at EACH octave. The scale-space is implemented as follows: Each octave is downsampled by half from the first image in ...
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Practical Applications of upsampling and downsampling

I'm a complete novice to digital signal processing, and I've started reading a few books on it. In particular, I've run across the concept of upsampling and downsampling. As I understand it, given a ...
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Z-transform of a downsampler

In this paper or multirate filtering, the author establishes the following mathematical relationship. Let $y_D$ be the output of a downsampler such that $$y_D[n] = x[Mn]$$ where $M$ is the ...
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2answers
487 views

Downsample Equiripple FIR filter

I am designing some Downsampling filters using the remez exchange algorithm (Matlab FDAtool). I see that some times i get a spike at the first and last coefficients. does anybody knows why is that? my ...
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1answer
903 views

Converting from stereo to mono by averaging

Hi I'm doing a past exam question about converting from stereo to mono. The scenario is below: The first question is: Explain why would this result in a noisy encoding. How is the noise ...
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259 views

Reference for Supersampling

I want to downsample images to arbitrary sizes using supersampling to avoid aliasing effect. The only two good explanations I found were on Wikipedia and everything2.com, but there are still gaps. ...
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2answers
3k views

How to extract vocal part from stereo audio signal?

I'm now processing MP3 file and encounter this problem. My MP3 is stereo encoded. What I want to do is extract vocal part for further processing(whatever mode of output signals, mono or stereo are ...
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3answers
2k views

Downsampling lowpass filter for audio: FIR or IIR?

I'm working on a real-time audio processing project in which I have to downsample a 44.1 kHz to a yet-to-be-determined lower sampling rate essentially for reducing computational complexity. I'm ...
7
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3answers
2k views

What is anti-alias pre-filter for preventing aliasing after under-sampling?

We know that the under-sampling results in aliasing and frequencies higher than half of the Nyquist rate is not distinguishable. I've a base band signal that I want to use the higher frequencies which ...
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3answers
456 views

What is the effect of aliasing on the magnitude of the autocorrelation?

I've a question about the effect of aliasing on the magnitude of autocorrelations. From a simulation in MATLAB, I don't see any effect of aliasing or any need to anti-alias filter when I take the ...
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5answers
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Why would I leave a signal oversampled?

I can't think of a better way for asking this question so I will start with an example. Suppose that I have an input signal with a max frequency of 50Hz (sampled at 100Hz). Now the signals of interest ...