signal-processing

Similarity between two signals: looking for simple measure

跟風遠走 提交于 2019-12-03 13:08:12
问题 I have 20 signals (time-courses) in group A and 20 signals in group B. I want to find a measure to show that group A is different from group B. For example, I ran xcorr for the signals within each group. But now I need to compare them somehow. I tried to take a maximal amplitude of each xcorr pair, which is sort a measure of maximal similarity. Then I compared all these values between two groups, but there was no difference. What else can I do? I can also compare frequency spectrum, but then

Transferring data using ultrasound

核能气质少年 提交于 2019-12-03 12:12:48
问题 Yamaha InfoSound and ShopKick application use technologies that allow to transfer data using ultrasound . That is playing an inaudible signal (>18kHz) that can be picked up by modern mobile phones (iOS, Android). What is the approach used in such technologies? What kind of modulation they use? 回答1: I see several problems with this approach. First, 18kHz is not inaudible. Many people cannot hear it, especially as they age, but I know I certainly can (I do regular hearing tests, work-related).

Niblack algorithm for Document binarization

瘦欲@ 提交于 2019-12-03 11:40:53
问题 i've this photo : and i'm trying to make Document binarization using niblack algorithm i've implemented the simple Niblack algorithm T = mean + K* standardDiviation and that was it's result: the problem is there's some parts of the image in which the window doesn't contain any objects so it detects the noise as objects and elaborates them . i tried to apply blurring filter then global thresholding that was the result : which wont be solved by any other filter i guess the only solution is

FFT Pitch Detection for iOS using Accelerate Framework?

放肆的年华 提交于 2019-12-03 09:55:55
问题 I have been reading up on FFT and Pitch Detection for a while now, but I'm having trouble piecing it all together. I have worked out that the Accelerate framework is probably the best way to go with this, and I have read the example code from apple to see how to use it for FFTs. What is the input data for the FFT if I wanted to be running the pitch detection in real time? Do I just pass in the audio stream from the microphone? How would I do this? Also, after I get the FFT output, how can I

Calculating the blur kernel between 2 images

浪尽此生 提交于 2019-12-03 09:21:52
Unlike the standard (and more challenging) de-blurring and super resolution scenarios, I have access to both the original (sharp) image G and it's blurred version B . I'm simply looking for the blur kernel h . So because B is taken using a real camera the relation is: B=G*h+N (where * denotes convolution and N is some additive noise) Naturally, this is an over-constrained problem since h is small in size compared to G and B and so every few pixels in the pair of images generate an equation on the entries of h . But what would be the simplest way to actually implement this? My thoughts so far:

how to improve the resolution of the PSD using Matlab

我的未来我决定 提交于 2019-12-03 09:06:57
I have and audio signal, which I read with Matlab, and use pwelch to get its PSD, here ist the code that I'm using [x,Fs] = audioread('audioFile.wav'); x= x(:,1) % mono [xPSD,f] = pwelch(x,hamming(512),16,1024,Fs); plot(f,xPSD); since the FS=96000 and I'm only interrested in Frequencies bellow 5khz, I would like to calculate the PSD only for the area, and also being able to adjust the resolution of the PSD ! any idea hwo to do that ! When calculating PSDs with pwelch , there is always a trade-off between spectral resolution, number of averages and the amount of data you need. My preferred way

2D circular convolution Vs convolution FFT [Matlab/Octave/Python]

痞子三分冷 提交于 2019-12-03 08:58:09
I am trying to understand the FTT and convolution (cross-correlation) theory and for that reason I have created the following code to understand it. The code is Matlab/Octave, however I could also do it in Python. In 1D: x = [5 6 8 2 5]; y = [6 -1 3 5 1]; x1 = [x zeros(1,4)]; y1 = [y zeros(1,4)]; c1 = ifft(fft(x1).*fft(y1)); c2 = conv(x,y); c1 = 30 31 57 47 87 47 33 27 5 c2 = 30 31 57 47 87 47 33 27 5 In 2D: X=[1 2 3;4 5 6; 7 8 9] y=[-1 1]; conv1 = conv2(x,y) conv1 = 24 53 89 29 21 96 140 197 65 42 168 227 305 101 63 Here is where I find the problem, padding a matrix and a vector? How should I

Acoustic Echo Cancellation (AEC) in embedded software

六月ゝ 毕业季﹏ 提交于 2019-12-03 08:57:24
I am doing a VoIP project on embedded device. I have built a sample using a 32bits MCU with a low grade audio codec. Now I found that there is echo issue on my device, that is I can hear what I said from the speaker. I have do some research and found that most appliaction use a DSP codec with acoustic echo cancellation feature. However, is it possible that I do the acoustic echo cancellation in the software, using my 32bits MCU? Can you adive the algorithm, or even source code:P, for doing acoustic echo cancellation? I know sophisticated method is not possible on a MCU, whereas a simple

Frequency response using FFT in MATLAB

别来无恙 提交于 2019-12-03 08:48:21
Here is the scenario: using a spectrum analyzer i have the input values and the output values. the number of samples is 32000 and the sampling rate is 2000 samples/sec, and the input is a sine wave of 50 hz , the input is current and the output is pressure in psi. How do i calculate the frequency response from this data using MATLAB, using the FFT function in MATLAB. i was able to generate a sine wave, that gives out the the magnitude and phase angles, here is the code that i used: %FFT Analysis to calculate the frequency response for the raw data %The FFT allows you to efficiently estimate

How to find tops and bottoms in time series?

匆匆过客 提交于 2019-12-03 08:46:26
问题 At first, this question can sound really stupid, but it is not in fundamental. Maybe, it can seem like unresolvable exactly by any algorithm, but I pretend to say it is. So question. I have chart, for example gold. I need to find where are tops and bottoms on time axial. The problem is I need to find where major upturns and major downturns start. The problem is that there is lot of small irrelevant upturns and downturns. Here is the picture for better understanding - the red spots are that I