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1500 questions
10
votes
6 answers
High pass filter of 0.01 Hz for EEG slow drifts
I am trying to make a high pass filter for electroencephalographic (EEG) datasets, in order to get rid of very slow drifts. However frequencies around 0.3 Hz are very important for the research these data serve.
I use Matlab and I tried various…
forsker_for_dsp
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10
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2 answers
How do you handle negative frequencies in the power spectrum of a complex signal?
When we apply the DFT operation on a real signal $x[n]$ to get $X[k]$,
then take the square magnitude of the $X[k]$, $\lvert X[k]\rvert^2$, the power spectrum is symmetrical.
You can take the positive frequencies or negative frequencies as the…
Mike
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10
votes
1 answer
How does noise reduction for speech recognition differ from noise reduction that is supposed to make speech more "intelligible" for humans?
this is a question that has interested me for some time now, mainly because I'm working on noise reduction for an existing speech recognition system myself.
Most papers on noise reduction techniques seem to focus on how to make speech more…
marlonfl
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10
votes
5 answers
Fast & accurate convolution algorithm (like FFT) for high dynamic range?
It seems that FFT-based convolution suffers from limited floating-point resolution due to evaluating everything around the roots of unity, as you can see in the $10^{14}$-factor error in this Python code:
from scipy.signal import convolve,…
user541686
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10
votes
3 answers
Capacity of AWGN channel
I am confused understanding basic concepts of communication over AWGN channels. I know the capacity of a discrete time AWGN channel is:
$$C=\frac{1}{2}\log_2\left(1+\frac{S}{N}\right)$$
and it is achieved when the input signal has Gaussian…
Mah
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10
votes
2 answers
Exponential moving average cut-off frequency
I am trying to implement a low pass filter from this example.
What is the cut-off frequency for this type of filter? Is it $$F_s \left(\frac{1-\alpha}{2\pi\alpha}\right)$$ where $F_s$ is sampling frequency?
jurij
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10
votes
1 answer
What is the easiest, most straight-forward way to prove this about minimum-phase filters?
Using the "unitary" or "ordinary frequency" or "Hz" convention for the continuous Fourier Transform:
$$ \begin{align}
X(f) \triangleq \mathscr{F}\{x(t)\} &= \int\limits_{-\infty}^{\infty} x(t) \, e^{-j 2 \pi f t} \, dt \\
\\
x(t) =…
robert bristow-johnson
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10
votes
1 answer
What kind of modulation is this?
I'm trying to find out what kind of modulation and encoding is used by my window cover remote control, aiming to implement the same on a Raspberry Pi to add a bit of home automation.
A colleague helped me sample the signal with an USRP and gave me…
jjmontes
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10
votes
3 answers
How does Siri recognize me saying "Hey Siri"?
I am trying to understand how my iPhone can continually listening for me saying Hey Siri, Alexa, Hey Cortana or Okay Google without quickly draining my battery down.
I imagined two kind of algorithm. One that record slice of time such as 10 ms wide…
nowox
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10
votes
1 answer
What happens when N increases in N-point DFT
I am curious about DFT, and I wrote a simple MATLAB code to test what happens when $N$ increases. I took a rectangular signal with length $L=15$, an then found th DFT of 16, 32 and 64 points. I looked at the plots of the DFTs, however I could not…
Canberk
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10
votes
1 answer
Why does the separable filter reduce the cost of computing the operator?
A separable filter in image processing can be written as product of two more simple filters. Typically a 2-dimensional convolution operation is separated into 2 onedimensional filters. This reduces the cost of computing the operator.
Why is the cost…
Iter Ator
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10
votes
1 answer
How can I estimate the spatial resolution of consumer grade electronics?
I have been looking at stereo vision applications, and one working example involves using two USB web cams, mounted together and calibrated.
Is there a way to estimate the theoretical spatial resolution of such a set up? The goal is to avoid…
Stephen
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10
votes
4 answers
Gaussian White Noise - Relation Between Distribution and Correlation
Im a beginner in signal processing so my question may be obvious.
A white noise has the property to have its autocorrelation function that is equal to
$$\mathbb{E}[f(t+\tau)f(t)]=\sigma^2 \delta(\tau).$$
We say that random signals can be Gaussian…
StarBucK
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10
votes
1 answer
Data decomposition method invariant to small shift and scale?
Is there a data decomposition method similar to eigenvalue that estimates projection matrix to reduce dimensionality but does not project similar vectors too far away in euclidian distance terms from each other if original data from the same class…
Chesnokov Yuriy
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10
votes
2 answers
Is spectral leakage due to windowing 'different' for the DTFT and DFT?
I'm currently trying to improve my foundational understanding of spectral leakage due to windowing. The more I have been reading about it, the more I'm starting to think that 'windowing spectral leakage' can mean two completely different things…
Izzo
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