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1500 questions
9
votes
1 answer
Rotating a 3D image
I've got a 3D image of non-isotropic voxels, to which I'm applying a general rotation. How could I go about determining an appropriate voxel size for the rotated image? I need to minimize loss of information, but avoid too much supersampling to keep…
Andrew Wood
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9
votes
1 answer
Scalogram (and related nomenclatures) for DWT?
My understanding of the scalogram is that, for a particular row, the scores of the projection of the input signal with the wavelet at a particular displacement is shown. Across rows, the same thing applies, but for dilated version of the wavelet. I…
Spacey
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9
votes
2 answers
Logarithmic fourier transform(LFT) on audio signal
I am trying to analyze the musics as possible as precisely.
Of course I tried FFT, but got some problems.
I found low frequencies have very low resolution than human's hearing. I tried very long time FFT to resolve this problem, but even analyzing…
Laie
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9
votes
2 answers
Where do RBJ's analog shelving filters come from?
In RBJ's Audio EQ Cookbook, the analog prototype for a low shelf filter is given as such:
$$H(s)=A\cdot\frac{s^2+\left(\frac{\sqrt{A}}{Q}\right)\cdot s + A}{A\cdot s^2 + \left(\frac{\sqrt{A}}{Q}\right)\cdot s + 1}$$
Where does this prototype come…
noshwins
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9
votes
2 answers
Fourier series of cycloid
What is the Fourier series representation of a cycloid?
The parametric representation of the curve is as follows.
$$
t=\dfrac{\theta-\sin\theta}{\pi}\\
x=\dfrac{1-\cos\theta}{\pi}
$$
The period is $2$, so the coefficients of the complex exponential…
tfpf
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9
votes
1 answer
What is the maximal frequency resolution for Matlab's STFT implementation spectrogram()?
Matlab's spectrogram() function calculates the STFT of a signal. It describes its NFFT argument as follows:
S = SPECTROGRAM(X,WINDOW,NOVERLAP,NFFT) specifies the number of
frequency points used to calculate the discrete Fourier transforms.
…
Andreas
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9
votes
1 answer
Texture detection and region properties on an image
I have an interesting problem that I'm trying to solve. So for example, if we have a black and white image containing two textures (A and B), I'm interested in knowing the pixel values of the boundaries that would completely cover the individual…
user1070502
9
votes
2 answers
Can Principal Component Analysis (PCA) Solve the Cocktail Party Problem?
I'm looking into the cocktail party problem and trying to figure out whether something like Principal Component Analysis is enough to separate out all the various voices at the cocktail party into its constituent sound sources.
If its not enough,…
hotmeatballsoup
- 153
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9
votes
1 answer
Digital filter coefficients from low-pass to high-pass
Given I have coefficients a0, a1, a2, b1, and b2, defining the difference equation for a digital filter as:
y[n] = a0 * x[n] + a1 * x[n - 1] + a2 * x[n - 2] - b1 * y[n - 1] - b2 * y[n - 2]
Which defines a low-pass filter with particular cutoff…
user2649681
- 201
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9
votes
1 answer
How can I detect potholes using an accelerometer mounted in a vehicle?
I am currently studying DSP and FFT, I am very new to this and have been doing electronics for a long time with Arduino and hobby projects. Recently, I am doing a project with the goal to map potholes along your daily commute in the car, measuring…
zacharoni16
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9
votes
5 answers
Piano pitch detection
I'm working on a piano tuning program and part of it requires real-time pitch detection. Here is the scheme I have so far which works to some degree but could probably use some refinement.
I'm capturing mono, 44.1kHz, 16-bit PCM audio in chunks of…
DrTodd13
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9
votes
3 answers
Spherical equivalent of Nyquist frequency
Let $\phi$ be a scalar function defined on the surface of a sphere. I have samples of $\phi$ at various locations on the sphere. I want to apply a spherical harmonic transform. I know that $\phi$ is 'band-limited' in the sense that it can be…
Fab von Bellingshausen
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9
votes
5 answers
Is a Fourier transform a sound way to analyse a transient signal?
I am currently working on a project that involves analysing transient signals from sensors.
While not actually part of the analysis itself, I discussed it with the team, and they are using an fft to analyze the transient measurement.
From what i…
Sclrx
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9
votes
1 answer
Detect human speech in realtime audio on mobile phones
I am looking to develop an Android app. As part of the functionality the app would require to randomly sample 3-5 seconds of audio and classify it as containing human speech or not. I understand that this concept is called Voice Activity…
Dony George
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9
votes
5 answers
Can someone help explain what this FFT workflow is doing to my signal, and why it works?
I am working with a piece of equipment that does acoustic analysis. It does this by acquiring a time domain signal and performing an FFT on it to extract the amplitude and phase at a single desired frequency, call it f0. Now, I understand the FFT.…
Ben S.
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