Most Popular
1500 questions
186
votes
5 answers
"River" detection in text
Over on the TeX stackexchange, we have been discussing how to detect "rivers" in paragraphs in this question.
In this context, rivers are bands of white space that result from accidental alignment of interword spaces in the text. Since this can be…
Lev Bishop
- 1,633
- 3
- 11
- 9
146
votes
8 answers
Why is the Fourier transform so important?
Everyone discusses the Fourier transform when discussing signal processing. Why is it so important to signal processing and what does it tell us about the signal?
Does it only apply to digital signal processing or does it apply to analog signals as…
jcolebrand
- 1,579
- 3
- 10
- 9
131
votes
5 answers
What does frequency domain denote in case of images?
I was just learning about the frequency domain in images.
I can understand the frequency spectrum in case of waves. It denotes what frequencies are present in a wave. If we draw the frequency spectrum of $\cos(2\pi f t)$, we get an impulse signal…
Abid Rahman K
- 2,377
- 5
- 20
- 23
118
votes
12 answers
What is the physical significance of negative frequencies?
This has been one of the holes in my cheddar cheese block of understanding DSP, so what is the physical interpretation of having a negative frequency?
If you have a physical tone at some frequency and it is DFT'd, you get a result in both the…
Spacey
- 9,817
- 8
- 43
- 79
117
votes
4 answers
Why is it a bad idea to filter by zeroing out FFT bins?
It's very easy to filter a signal by performing an FFT on it, zeroing out some of the bins, and then performing an IFFT. For instance:
t = linspace(0, 1, 256, endpoint=False)
x = sin(2 * pi * 3 * t) + cos(2 * pi * 100 * t)
X = fft(x)
X[64:192] =…
endolith
- 15,759
- 8
- 67
- 118
107
votes
4 answers
What is the difference between a Fourier transform and a cosine transform?
In speech recognition, the front end generally does signal processing to allow feature extraction from the audio stream. A discrete Fourier transform (DFT) is applied twice in this process. The first time is after windowing; after this Mel binning…
Nate Glenn
- 1,187
- 2
- 8
- 6
101
votes
6 answers
Why should I zero-pad a signal before taking the discrete Fourier transform?
In an answer to a previous question, it was stated that one should
zero-pad the input signals (add zeros to the end so that at least half of the wave is "blank")
What's the reason for this?
Jonas
- 3,071
- 3
- 20
- 19
86
votes
4 answers
What is meant by a system's "impulse response" and "frequency response?"
Can anyone state the difference between frequency response and impulse response in simple English?
Ant's
- 1,062
- 2
- 9
- 9
78
votes
9 answers
Why do we use the HSV colour space so often in vision and image processing?
I see the HSV colour space used all over the place: for tracking, human detection, etc... I'm wondering, why? What is it about this colour space that makes it better than using RGB?
porridge
- 781
- 1
- 6
- 3
77
votes
4 answers
What are some free alternatives to SIFT/ SURF that can be used in commercial applications?
As far as I understand, both SURF and SIFT are patent protected.
Are there any alternative methods that can be used in a commercial application freely?
For more info on the patent check…
Andrey Rubshtein
- 2,850
- 1
- 20
- 23
70
votes
12 answers
Is deep learning killing image processing/computer vision?
I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged.
My concern is, since deep learning doesn't need feature extraction and almost no input…
Tony
- 803
- 1
- 7
- 6
69
votes
8 answers
How do I implement cross-correlation to prove two audio files are similar?
I have to do cross correlation of two audio file to prove they are similar.
I have taken the FFT of the two audio files and have their power spectrum values in separate arrays.
How should I proceed further to cross-correlate them and prove that…
Warrior
69
votes
2 answers
Why so many methods of computing PSD?
Welch's method has been my go-to algorithm for computing power spectral density (PSD) of evenly-sampled timeseries. I noticed that there are many other methods for computing PSD. For example, in Matlab I see:
PSD using Burg method
PSD using…
nibot
- 3,803
- 5
- 29
- 40
68
votes
10 answers
Algorithm(s) to mix audio signals without clipping
I'd like to mix two or more PCM audio channels (eg recorded samples) digitally in an acoustically-faithful manner, preferably in near-real-time (meaning little or no peek-ahead).
The physically "correct" way to do this is summing the samples.…
bryhoyt
- 1,423
- 3
- 13
- 14
65
votes
6 answers
If humans can only hear up to 20 kHz frequency sound, why is music audio sampled at 44.1 kHz?
I read in some places that music is mostly sampled at 44.1 kHz whereas we can only hear up to 20 kHz. Why is it?
Soham De
- 752
- 1
- 5
- 7