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## magical Black Hole image

inThe Event Horizon Telescope team of course deserves a huge amount of credit for their results. But it's interesting how they got there. ...

The Event Horizon Telescope team of course deserves a huge amount of credit for their results. But it's interesting how they got there. Here's an article with some non-technical discussion: https://fivethirtyeight.com/features/forget-the-black-hole-picture-check-out-the-sweet-technolog y-that-made-it-possible/ Their data is too noisy to actually create a black hole image. So they a

## Efficiency of Midi->Freq and back

inI'm writing something with a lot of conversions between midi and frequency in a timing tight situation and I'm wondering about efficiency. (in C)...

I'm writing something with a lot of conversions between midi and frequency in a timing tight situation and I'm wondering about efficiency. (in C) What are the community's experiences with this? Would a 1 or 10 cent interpolated lookup table be more efficient? Is there a way to make the log less expensive? Does caching and comparing the last input and output help? Thanks for any insig...

## High-order EMA works great - but why?

inI have a classic digital PLL with multiplier-based phase detector, intended to lock at 50Hz. The sampling frequency Fs is 25kHz, the...

I have a classic digital PLL with multiplier-based phase detector, intended to lock at 50Hz. The sampling frequency Fs is 25kHz, the loop filter bandwidth varies between Fc=10Hz to 40Hz, as I am experimenting with different filter structures. The PLL itself works like a charm and my reference filter is a 500th order FIR: fir1(500,Fc/(Fs/2)). To a reasonable degree the loop converges to a ...

## Homodyne complex frequency shift

inHi, the input signal is sin(t), I multiply it with cos(t) to get the I component and sin(t) to get the Q component. So...

Hi, the input signal is sin(t), I multiply it with cos(t) to get the I component and sin(t) to get the Q component. So then I(t)=sin(t)*cos(t)=0.5*sin(2t) Q(t)=sin(t)^2 I would expect only the DC component to persist, but instead I have two quickly wiggling waves. What is missing to shift 1kHz to DC without introducing the mirror frequencies? Thanks in advance!

## FFT interpolation Matlab

inHi, I am trying to use interpolation to detect an FFT peak between bins however my interpolation results in the same peak as the FFT. I am...

Hi, I am trying to use interpolation to detect an FFT peak between bins however my interpolation results in the same peak as the FFT. I am inputting a 50Hz sine wave.. Sampling freq is 6500hz and I have 2048 sample points. There fore my bin freq is 3.17hz which multipled out gives me a 50.8hz nearest bin frequency which is what my code is giving me. I am trying to see where my i

## Ultrasound beamforming

inHi, A typical beamforming method widely used in ultrasound technology is to apply delays between channels and then summing the signals of all the...

Hi, A typical beamforming method widely used in ultrasound technology is to apply delays between channels and then summing the signals of all the channels. However, when properly calculated delays are applied, it could happen that the phase of the arriving signal is 180 deegres (half the ultrasound wavelength) shifted between channels and summed amplitude is decreased. This results

## Load disturbance sensitivity function in control loops

Hi, I'm a bit confused about the load disturbance sensitivity function in control loops. Basically, I have a design where the load disturbance...

Hi, I'm a bit confused about the load disturbance sensitivity function in control loops. Basically, I have a design where the load disturbance sensitivity function has a maximum of 5 at a frequency of 300 Hz. I'm not sure I understand this metric correctly. Does it mean that a load variation of 10% at a frequency of 300 Hz would create a variation 5 times higher on the output? The formula...

## Why does it say "Toeplitz matrix, so we only need to calculate the first row and column of the matrix"?

inHi, I know Toeplitz matrix has the same value along its diagnose line. I think the first row value gives all the value of the Toeplitz matrix,...

Hi, I know Toeplitz matrix has the same value along its diagnose line. I think the first row value gives all the value of the Toeplitz matrix, why the author said in his way. /////////////// Toeplitz matrix, so we only need to calculate the first row and column of the matrix Thanks for reading

## DCT in video compression

inThe mp3 standard uses the discrete cosine transform (DCT), rather than the full DFT. Doesn't that imply throwing away half the...

The mp3 standard uses the discrete cosine transform (DCT), rather than the full DFT. Doesn't that imply throwing away half the information? Can anyone explain this? -- Rich

## Counter and length of count

inSomebody check the sums which was fun working out. I have a sensor which gives out 4096 pulses per revolution. This is attached to a motor...

Somebody check the sums which was fun working out. I have a sensor which gives out 4096 pulses per revolution. This is attached to a motor which turns at 1000 rpm. I need to count by using an integer in increments defined by a signed 64 bit integer. The question is, how long can it count for at this speed before the integer overflows? 64 bits is about + or - 9.23 x10^18 count in on

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