Questions tagged [decimation]
Decimation is a technique for reducing the number of samples in a discrete-time signal.
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Understanding the Farrow Filter
I found the following diagram of a Farrow Filter online:
As far as I understand the purpose of a Farrow filter is to interpolate samples at a fractional ratio.
For example: we have an ADC sampling at ...
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ADC output rate, undersampling and decimation
I have an ADC working with a sample rate of 960 Msps, my signal being located at the 3rd Nyquist region (I am undersampling). Input signal bandwidth is centered at 1200 MHz with a bandwidth of 120 MHz....
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Effect of aliasing on time-domain SNR
I'm trying to reconcile the fact that decimation without low-pass filtering does not modify the ratio of signal to interference power in the time domain with the fact that, in the frequency domain, ...
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I'm struggling to understand the FIR Filter and its application
I'm new to GNU Radio, and I was watching this video However, I didn't quite understand the purpose of the FIR Filter. I know what decimation or downsampling is because I have the book "Digital ...
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Is this proof valid?
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}) = ...
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Sample rate change using Lagrange interpolator
I'm trying to understand how to make Sample rate change by a non integer factor say $K=1.0012$
In real hardware I will be using cubic polynomial but for now I have chosen a linear interpolator. I have ...
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DSP library for Software Defined Radio
Can anyone recommend a good C library for SDR? To be more specific I just need a function in C to compute coefficients for CIC compensation filter (I need to do it in real time, so Matlab is not an ...
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How to Dereverberate Speech taken in an Auditorium with Reverberation Time of 3.8 to 4 seconds
I'd like to cancel echoes from a Talk recorded in a large extremely reverberant auditorium. It's unintelligible as recorded, and I'm hoping to make it intelligible by echo cancellation.
Audio was ...
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Decimation effect on the spectrum
If I have a sampled cosine wave signal with Fc = 80kHz and Fs = 200kHz (so the Nyquist region is between 100kHz and -100kHz) and I want to preform a decimation by the factor of 2.
Will my input signal ...
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ADC Resolution after oversampling
I am using an ADC (ltc2378) with a resolution of 20 bits.
Based on the datasheet this resolution corresponds to an LSB calculated by the equation ($2 V_{\text{ref}}/2^{20}$), i.e., 9.536 µV.
In order ...
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Use of DFT for Decimating Channelizers
Decimation by a factor $D$ is the combination of anti-alias filtering and down-sampling (selecting every $D$th sample). The frequency bands where aliasing occurs will be centered of $nf_s/D$ for $n=0,...
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How does rate reduction work in a decimator with even valued gain?
Cascaded integrator-comb (CIC) filters are used in decimators, and decimators with a gain that is a power of 2 are popular (at least at my workplace) because the gain can be normalized with a right ...
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Smart MEMS microphones
Edit: from Wikipedia's Delta-sigma modulation it looks like since the microphone basically is an ADC, and that as such mics with PDM output may use a Σ‑Δ modulator internally. Also, from Selecting PDM ...
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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 ...
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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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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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Multirate Control System Transfer Functions
I'm interested in oversampling the inputs to a digital controller to increase the SNR of the input process variable signal. I've read on this site and in articles like the one below that it is not ...
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Efficient CIC Decimation Filter in C
Does anyone have advice on efficient CIC Decimation filter implementation. I designed a basic 4th order CIC filter with a 64 decimation ratio in C (below).
I am currently testing this on a Sharc SC589 ...
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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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Decimation filters: IIR vs. FIR
I just read this article on decimation filters. In particular, in section 2.3.3 it is strongly suggested that FIR filters are advantageous, because you only need to calculate every $M$th sample, where ...
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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 ...
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Taking every third value or the mean of three
Referring to Sampling, filters, windowing, FFT. From theory to help on this coding list with the figure, I now have some more questions.
How will taking every third of the 48 kHz vs. taking the mean ...
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Performing Sample-Rate Conversion on Subchunks of an Audio Signal
I have implemented sample-rate conversion (SRC) from scratch in my hobby music player, and it worked fine. However, originally, the music player loaded entire audio files into memory and performed the ...
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Lowpass Filter for Lock-In-Amplifier
I am implementing a Lock-In-Amplifier in Python with scipy for measurements with light with a decimation afterwards. Right now, this is implemented with an average. This works fine, but I am trying to ...
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Shift of the signal spectrum to the desired frequency
I have a task to select only the area I need from the signal and shift its spectrum.
I am digitizing the signal at 48kHz. A useful signal for me is in the region of 5500-5995Hz and 6005-6500Hz. In ...
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More Efficient Frequency Shift + FIR Decimation
I am dealing with complex IQ data from a software defined radio. I'd like to digitally shift the spectrum by some amount to center an off-center signal, then decimate down to that signal only. ...
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Z Transform of M-Fold Decimation
I know this is probably a common question, but after some searching I think that my version of the question is slightly different -- apologies if this is a repeat. I have seen that it is inaccurate to ...
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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 ...
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Decimation with dynamic factor in GNU Radio
In a GRC flowgraph I have a custom OOT block which periodically sends a PMT message to the "command message port" of the "UHD: USRP Source Block" (for set the RF center frequency
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Decimation filter that throws away every $N$th sample, keeping multiple samples: is it valid?
While working on an existing project, I came across a piece of code that does a decimation filter in a way that I find not obvious.
In this code, every 6th sample is being thrown away. The result is ...
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Can I optimize band-pass FFT filter with skipping values instead of zeroing them when decimating?
I currently use very simple band-pass filter: FFT->Keeping needed, zeroing not needed->iFFT->decimation with skipping
This works perfectly for my needs (I apply envelope after filter so no ...
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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 ...
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Implementation of CIC filter using floating point
I am trying to implement a CIC filter and was reading through the literature and found that CIC filter cannot be implemented using floating point. I am unable to understand why that would happen. The ...
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difference beetween decimate an array and decimate function
i'am actually comparing data and i got a question that i cannot anwser,
here is what i understand.
nanometrique move
X[::256] : decimate and take 1/256 point in the vector (blue)
decimate(X, 256, ...
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Can multi-rate operations of decimation and interpolation can be used to implement a rate change by a factor an irrational number?
I know that common rates are integer values like 2 or 3, but can multi-rate operations of decimation and interpolation can be used to implement a rate change by a factor of an irrational number? ...
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How does decimation work without losing samples?
For example, changing the frequency from 32.768Mhz to 2kHz there is a scale down of 16384.
From the algorithms I've seen you have to discard 16384-1 samples and only count the 16384th sample. However, ...
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Is there a way to use decimation or linear interpolation to shrink or stretch an audio signal in the time domain?
I am able to shrink/stretch an audio signal using Python code for a phase vocoder, as well as the stretchAudio function from Matlab's Audio Toolbox. Although both methods do indeed alter the audio ...
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Direct and Transpose Polyphase Multirate Processing
Polyphase implementations of upsampling/ interpolation and downsampling/ decimation, after having invoked the Noble identities, are presented as follows (taken from Proakis):
(Three-Channel Polyphase ...
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Design FIR filter with half zero coefficions
I noticed a lot of hardware IC use special FIR filters with half zero of coefficients to minimize multiplication operations, especially in decimators/interpolators. E.g.
[ 6 0 -19 0 47 0 -100 0 192 0 -...
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Filter Cascade: Additions and Multiplications per input sample
Recently I was reading "Optimum FIR Digital Filter Implementations for Decimation, Interpolation, and Narrow-Band Filtering) by Crochiere and Rabiner (1975).
To estimate the number of decimation ...
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Designing FIR filter for real-time decimation of audio on embedded system
I need to design a lowpass FIR filter to downsample an audio stream that is oversampled at 250Khz. The goal is to write a real-time audio player of an audio stream on an embedded system which is ...
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Given a wide band signal with equal SNR over the whole spectrum, what should the stop band attenuation be for a decimation filter?
Imagine an incoming signal with $60$ dB SNR over the whole spectrum.
I want to decimate this signal by a factor of, say, $40$, while maintaining a $60$ dB SNR in the remaining frequency range.
What ...
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Decimation FFT Result
In my Signal Processing class we just learned decimation however after messing around in Matlab trying an example of decimation, I just can't understand what's happening.
I get the introducing twi ...
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Oversampling, decimation and Nyquist
I know this is a bit of a fundamental DSP question but I want to finally understand this and I think I need some help to finally put it all together.
Let's say I have an RF complex sampling ADC with a ...
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Resampling FIR coefficients
I have received from a client a 32-coefficient FIR filter running at 1 kHz. I would like to adapt the filter to a 24-coefficient FIR filter running at 750 Hz while preserving the 0-375 Hz frequency ...
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Matlab CIC decimator output mirrored
I am trying to use the dsp.CICDecimatior function and comparing the output to a C code algorithm that I have. The CIC decimator is configured as decimation factor of 8 , 3 sections and differential ...
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Decimation Question about using a low pass filter before downsampling
I have a bunch of audio files that have a sample rate of 380kHz, however I would like to reduce this sampling rate to 44.1kHz. From doing some research online, it seems like I will have to use a low ...
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Does resampling cause phase shifts?
I have a signal sampled at 40MHz, I would like to resample it to 37MHz. The signal is not periodic, I did resampling with Matalb resample function and it doesn't cause phase shift (as far as I ...
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Composition of interpolation and decimation matrices
I understand that interpolation is a linear transformation of a signal vector that combines interleaving the elements of the input vector with zeros followed by a filtering operation to remove any ...
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Decimation with IIR filter altering amplitude of signal
I'm downsampling a signal through decimate (scipy implementation), but the result has a different amplitude than the original signal, which if I understood correctly, shouldn't happen. The original ...
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