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Questions tagged [decimation]

Decimation is a technique for reducing the number of samples in a discrete-time signal.

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21
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5answers
3k views

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 ...
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1answer
11k views

Downsampling a signal with decimate

I'm experimenting with decimating a signal, in this case a unit impulse. I'm using Python, with pylab. First, I create a unit impulse, and decimate it by 5. ...
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1answer
3k 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 ...
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2answers
4k views

Design of the low pass filter when decimating

I am filtering an audio signal into various sub-bands in C and would like to decimate the signal by 2 in the lower frequency bands to reduce processing overhead. I get that this involves low-pass ...
4
votes
1answer
900 views

Timing syncronisation using polyphase decimation filter

This question is regarding application of polyphase decimation filter in symbol time correction. How does choosing a perticular "polyphase branch" in a polyphase decimation filter result in timing ...
4
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3answers
642 views

Image Pyramid Without Decimation

I have an image processing algorithm which uses Gaussian and Laplacian Pyramid Decomposition. At each level of the pyramid the algorithm decimates the previous level by a factor of 2. The LPF the ...
4
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2answers
2k 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: ...
4
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2answers
1k views

Difference between Sub Sampling and Down Scaling of Images

I know that there are many ways to upscale (interpolate) an image using bilinear, bicubic, sinc... Somehow, these same algorithms can also be used to downscale an image. But when it comes to ...
3
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4answers
2k views

Basic method for 2x oversampling?

I would like to know if the following method of 2x oversampling is correct: Interpolate: Take an original signal sampled at 44100Hz as input Upsample by adding a zero after each original sample to ...
3
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1answer
3k views

Can you decimate / downsample a signal in frequency domain just like you can interpolate / upsample it?

To interpolate a signal I can just zero pad it in the frequency domain. If I want to decimate the signal, can I just discard some part of the frequency domain? So in MATLAB this works: ...
3
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1answer
2k views

Does lowpass filtering and decimating improve SNR?

I did not manage to find clear answers to this question: does decimation after an appropriate lowpass filter improve the signal to noise ratio? To investigate this question, I considered data ...
3
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2answers
83 views

Besides computational costs, is filtering, decimating, then filtering different from just filtering?

Background: I have a variety of BPSK which uses a raised cosine transmitted pulse shape: $$ h(t) = {1 \over 2}\, (1+\cos(\pi t))\, \Pi(t/2) $$ After matched filtering in the receiver, the end result ...
3
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0answers
36 views

Proper way to implement a decimation

I have an input signal with bandwidth 2.5 MHz. Let's say it's filtered using analog Butterworth low-pass filter. I would like to sample the signal using AD9203 10-bit 40 Msps ADC. If I understand ...
3
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7answers
6k 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 ...
2
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3answers
1k views

How to design very narrow, sharp lowpass filters - Only DC needed?

I asked exact the same here one year ago: One year ago question I asked this question again here, because after one year, I have learned more about DSP and am thinking ways to improve it. Filter ...
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5answers
4k views

How to design very narrow band, very sharp low pass filters - Only DC needed?

I am using a DSP processor to sample signals at 108kHz and I only want to get the DC part out of it. Such a high sampling rate is used because I want to use oversampling to reduce quantization noises. ...
2
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2answers
5k views

What is the point of decimation?

The following makes sense to me: Decimation reduces the number of samples so it reduces the amount of data that is metered across networks and reduces the processing time for chips. That sounds great....
2
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1answer
395 views

Cut-off frequencies for fractional sample rate adjustment

We have a signal sampled att 22 kHz that we want to interpolate to 40 kHz. So we can do this by upsampling by a factor 20, then downsampling by a factor 11. My question regards the choice of cut-off ...
2
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2answers
2k views

Advantage of using FIR Polyphase Decimator over just computing FIR output every D samples

Let's say you want to implement an FIR filter $h[k]$ with $L$ taps and downsample the output: $v[k] = x[k] * h[k]$ $y[m] = v[kD]$ The "naive" way would be to compute all the samples of $v[k]$, then ...
2
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1answer
1k views

Polyphase decimation matlab [closed]

I am new to DSP, and currently trying to implement a simple polyphase decimation program in matlab. M is decimation factor, x is input (for now it is a square wave 8096 samples), y_polyDec is result ...
2
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1answer
326 views

How much to decimate?

What I don't understand is the connection between the sample rate, the baud rate, decimation and using convolution or correlation. I'm sampling at 2048000 Hz but I don't know my baud rate, I ...
2
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1answer
68 views

Decimating physics data

At work we run a physics simulator (video game) that operates in an inner loop at 360 Hz. Data from that inner loop is collected 60 times a second and sent out to hardware (a force feedback steering ...
2
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1answer
133 views

Decimating Long Data in Chunks

I have a very long data up to 8 millions of samples and want to decimate it to order of 1000s. I'm using following Matlab code to do this: ...
2
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1answer
312 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 ...
2
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1answer
961 views

IIR/FIR filtering before decimation?

I am trying to design a low pass filter to apply before resampling the sensor's output at a lower rate, however I am not quite sure how to choose between the IIR and FIR fitlers. Matlab by default, ...
2
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2answers
246 views

Decimating a discrete time cosine function

Let $x[n] = \cos(wn)\ \ $ be our signal. Let the other signal be $x_2[n] = \cos(2wn)\ \ $ . The spectrum of $x[n]$ and $x_2[n]$ are well defined and consist of impulses at the relevant frequencies ...
2
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1answer
293 views

Reordering frequency translation and decimation

I'm trying to understand the behavior of two different methods of decimating and frequency translating a signal. At this point, I'm only swapping the translation and decimation; I'm not doing any ...
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5answers
7k views

Output gain when upsampling and downsampling

Do the processes of upsampling and downsampling affect the magnitude of the transform of a signal? And if not, why am I seeing everywhere that a filter with gain different from 1 is applied after up/...
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1answer
1k 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
672 views

scipy.signal.decimate vs array operations

The following program generates a signal with a bit of noise according to some bits. I then try to decode the signal using convolve and decimate. 2 problems I notice: The whole this gets thrown out ...
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1answer
3k views

MATLAB: Decimation image

I'm trying to decimate given picture Vertically. Horizontally. Horizontally + Vertically. I know that I should use low-pass filter* and then downsample** it not to see any aliasing in image. To this ...
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2answers
6k views

Selecting the Low Pass FIR Filter, Decimation, DSP

I'm studying DSP, but I have weakness about it. I was reading this: http://www.eetimes.com/document.asp?doc_id=1275556 But, I don't know how select the Low Pass Filter. I am assuming that this ...
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3answers
561 views

Upsample / Downsample a Signal from 1920.93Hz to 1920Hz [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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1answer
3k 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 ...
1
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1answer
286 views

Decimate signal by 64

I have a 16bit SAR ADC sampling at 6.4kHz. The Anti-Aliasing Filter is a active 4th order Bessel lowpass (2x LTC6081) with -3dB at 200Hz and -80dB at 3.2kHz. Now I want to decimate these 6.4kHz to ...
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1answer
707 views

Resampling time series to regular array, then downsampling (Butterworth)

Long time reader, first time poster. I have a few very simple questions that are troubling me and I am hoping that one of you guys can help me out. Setup & Aim: I have a time series that I want ...
1
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1answer
971 views

Disadvantage of high downsampling rates with CIC filters

For a lock-in amplifier I am downsampling the demodulated baseband signal prior to the final low pass filtering. This lock-in amplifier is implemented on an FPGA (myRIO of National Instruments). ...
1
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1answer
205 views

Resampling: how many samples to zero-stuff or down sample?

I am a little confused about how resampling works with one filter. I get why you choose the lower nyquist cutoff when you combine both interpolation and decimation for resampling by a rational ...
1
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1answer
509 views

Efficient implementation of FIR comb/decimating filter

I'm working on trying to find an efficient way to implement a FIR comb/decimating filter. For a given "prototype" low-pass filter $ H(z)$, a comb that "repeats" $L$ times in the frequency domain can ...
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0answers
30 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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0answers
151 views

Decimation Aliasing

Lets say you have a signal which is sampled at rate $f_s$ and the bandwidth after sampling is $B$. Now you want to decimate this signal with a new sample rate $f_{s, new}$ where $f_{s, new} < f_s$ ...
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0answers
130 views

Interpolated FIR (IFIR) for decimation

I'm interested in implementing an optimized 5x decimation stage. However it seems the resources needed are significantly more than 4x or 8x composed of cascaded 2x stages. For general purpose FIR ...
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0answers
68 views

Choosing the right decimation number

I am a hamradio hobbyist with little knowledge in SP. I have to decimate the sampling rate of the received FM signal so I can get to the sampling rate that is supported by the sound card of my ...
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0answers
117 views

How are filters for polyphase decimation like?

I know in naive decimation the signal should filtered by a low-pass filter with cutoff frequency equals to Nyquist rate.I don't know how the filter banks like for polyphase decimation. Are them still ...
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0answers
112 views

Filtering and decimating input as sections in multiple stages

What would be my options to decimate a large input signal available only in sections (or blocks) due to DMA type of interface? The FIR should be about order of 18 only and the total decimation factor ...
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0answers
259 views

Symbol timing recovery algorithms

I am trying to implement the symbol timing recovery loop and for that I have chosen two algorithm to compare my results one is feedforward and Gardner TED. One thing that is confusing me is smoothing ...
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0answers
717 views

What is the output sequence of a Decimation filter [closed]

Consider x(n) as input, y(n) as output & h(n) as filter coefficient. The filter is of 16 taps(N=16) from 0 to 15. The decimation factor of the filter is 4. When I apply x(n) to this 16 tap ...
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0answers
213 views

RLS adaptive filter

I am using an adaptive RLS adaptive filter for noise cancellation. My sampling freq. is 500 Hz, but I am interested in only frequencies of up to 60 Hz. I filter the input and the reference signal to ...
0
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4answers
230 views

What's the advantage/disadvantage of oversampling followed by decimation, verses sampling at the correct rate to begin with?

I read somewhere that oversampling somehow reduces sampling noise? How to quantify the reduction in noise? and why would it reduce noise if you are decimating the oversampled signal. What's the ...
0
votes
2answers
2k 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 ...