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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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### 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 ...
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. ...
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 ...
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 ...
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 ...
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 ...
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: ...
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 ...
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 ...
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: ...
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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
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....
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 ...
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 ...
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 ...
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 ...
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 ...
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: ...
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 ...
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, ...
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 ...
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 ...
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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### 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 ...
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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### 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 ...
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 ...
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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### 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 ...
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 ...
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 ...
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). ...
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 ...
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 ...
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 ...
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 $f_{s, new} < f_s$ ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
213 views

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 ...