# Questions tagged [sampling]

Periodical measurement of an electronical property of a system, most often voltage.

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### Why are digital oscilloscopes still so expensive?

I'm a beginner in hobby electronics and I am wondering why digital oscilloscopes are still so expensive? In times of cheap GHz CPUs, USB 3, ADSL modems, DVB-S receivers, blu-ray players which all of ...
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### How do digital oscilloscopes achieve such high sample rates?

From the perspective of data capture, how is this achieved? If I wanted to implement a home-made digital device to capture high frequency analogue signals, what are my options? So far, I've only come ...
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### Why is the Nyquist data rate lower than the Shannon data rate?

In the book Computer Networks, the author talks about the maximum data rate of a channel. He presents the Nyquist formula : C = 2H log$_2$ V (bits/sec) And gives an example for a telephone line : ...
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### How is 10G Ethernet physically possible? [closed]

10 gigabit Ethernet means that 10 billion bits are transmitted every second, but I don't understand how this is physically possible (let alone 100G Ethernet). The fastest CPUs today only run at ~8GHz, ...
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### Why sample at a certain frequency just to immediately downsample it?

I apologize if this question is not well-posed. I'm reading a paper that claims the following: The magnetometer vectors are sampled at 100 Hz. The detector filters and down samples the vectors down ...
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### Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?

In the quest for a not so expensive PC scope/logic analyzer, I have found a nice little device it looks very well done and I know it will do the job. However looking at the specifications, I ...
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### Why do oscilloscopes list max bandwidth separate from sample rate?

I would figure that if a scope has a sample rate of 200 MSa/s, it should be able to measure signals up to its Nyquist frequency, 100 MHz. But there are a lot of scopes whose max bandwidth do not match ...
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### Why doesn't aliasing of broad band noise 'pile up' in the sample band?

I recently built a simulation to study sampling, the effects of aliasing and the effects of anti-aliasing filters on the sampled signal. For fundamental frequencies above the sample band it's obvious ...
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### When is it required or permitted to sample below Nyquist rate

I have searched past questions and answers on this platform but none answers this question. A prof said it is possible to sample below Nyquist rate under certain conditions. I will like to know, first,...
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### Exactly what is the role of the zero-order hold in a hybrid analog/digital sampled-data system?

I'll admit, I am asking this question rhetorically. I am curious what answers will come back out of this. If you choose to answer this, make sure you understand the Shannon-Nyquist sampling theorem ...
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### Why does increasing the sampling rate make implementing an anti-aliasing filter easier?

From an answer to a question regarding sampling rate and anti-aliasing filter I read the following: The closer you get to the theoretical minimum sample rate, the more difficult the analog filter ...
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### What is the "Nyquist" rate for sampling the derivative of a signal?

Background: I'm sampling the current through a capacitor. The signal of interest is the voltage across the capacitor. I will digitally integrate the current measurement to obtain the voltage. ...
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### Maximum sample rate of Arduino Duemilanove?

G'day all! I have an Arduino Duemilanove hanging around spare at the moment and thought I might try a few audio interfacing projects. I'm just wondering what sort of sampling frequency I can achieve ...
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### Shannon-Nyquist - only for repeating signals?

This was triggered by the comments in this question. I'm using this definition of the Shannon-Nyquist theorem (form wikipedia): If a function x(t) contains no frequencies higher than B hertz, it is ...
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### Word or phrase to describe how frequently a value is measured

When writing software for instrumentation, it is often required to specify a small gap of time between taking measurements. Say for example that 250 voltage measurements must be taken, and they must ...
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### Lossless compression technique for digital signals in an embedded system

Here's the scenario: I have an embedded system where an ADC logs a 16-bit potentiostat sample every 2 seconds. The system continues to record data for weeks, making memory usage a concern. Instead of ...
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### Can the Nyquist sampling rate also apply for the human eye the same as in electronics? [closed]

In electronics the Nyquist sampling rate shows you the maximum frequency that could be sampled without aliasing. So if the human eye is able to see 24fps does it mean that you can see all the ...
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### Differences between Interrupts and sampling for hardware button?

I have a hardware button I connected to an interrupt, but my problem is it bounces a bit, making the button press unreliable. I think a good deal of these issues would be solved by sampling in the ...
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### How to achieve coherent sampling in practice

In the context of measuring a sinusoidal source with an ADC, coherent sampling (i.e. capturing an integer number of periods) allows the use of a rectangular window without spectral leakage. How does ...
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### What's the difference (electrically) between AC- and DC-coupled sampling circuits?

I've noticed that in analog signal acquisition hardware you see two paradigms: AC-coupled and DC-coupled. Typically AC-coupled hardware is less expensive, and basically has a 20 Hz high-pass filter ...
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### Fast Fourier Transformation of incomplete signals

I would like to perform a FFT on a signal with equally sampled values of which some are missing. (Actually, they are not even missing, but simply erroneous, so I can't use them, but I can detect when ...
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### Highest ADC input signal frequency for atmega8?

I am trying to make a simple project which involves acquiring some data from the adc of atmega8 chip and then sending that data to UART. But I cannot figure out what would be the maximum limit of the ...
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### Simple low pass digital filter implementation for non-uniform sampling?

I have a system sampling an analog input and I want to filter that value using a simple, first order filter. EG something of the form: Yn = A*Xn + B*Yn-1 However I have no control over the ...
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### Techniques for digitally copying video laserdiscs

I’m attempting to design a system that can back-up the information stored on a video laserdisc by interpreting the RF signal generated by the photodiodes within the optical deck of the player. The RF ...
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### Is there an efficient way for synchronising audio events real-time with LEDs using an MCU?

I'm working on a project in which LED lights synchronise with audio events. I'm not referring to reactive LED projects that read the ADC from audio amplitude or spectrum, but about having some ...
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I need to calculate the exact sampling time or sampling rate for my setup on a STM32F205. I have the ADC setup as follow: ...
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### 16-bit or 24-bit converters?

I wanna build some DSP effects on, for example STM32F4 processor, with frequency 96 or 192 KHz. Are 16-bit converters (ADC and DAC) enough for that kind of operation? Can I hear a diffrence when ...
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Is it possible to increase the resolution of an ADC by supersampling on a PIC24F ADC, which has 10 bits of resolution and is implemented using a successive approximation engine? Speed is not critical -...
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### Anti-Aliasing filter design

I appreciate that different applications have different criteria, but could someone give a ball park figure of how much attenuation is needed for an anti aliasing filter at the Nyquist frequency to ...
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### Calculating FFT for only part of full frequency range?

Earlier I asked a question here about performing FFT at lower frequencies but still at high sample frequencies. I was under the impression that the FFT was inherently calculated at every frequency 0->(...
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### Equivalent time sampling on microcontrolers

I must admit, I don't know too much about analog electronics but I am keen to know if it possible to construct an equivalent time sampler (ETS) using the A/D's on a micro. I hope this question isn't ...
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### Relationship of FFT Size, Sampling Rate and Buffer Size

I am asking this question because I want to make sure I understand the relationship of FFT length, the sampling rate and the buffer size. This question is with respect to the CMSIS DSP library, ...
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### Is there any solution to high-precision high-side sampling current measurement?

I want to do some high-precision current measurement. (Voltage up to 20V and requires current to be shown in 0.1mA resolution, current can be up to 4A.) The simplest is low-side sampling by MCP3421: ...
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### In a Delta-Sigma ADC, does noise shaping bring the noise to the signal's frequency?

I'm trying to understand the Delta-Sigma ADC. It is known that it pushes the quantization noise to be in the higher frequencies (noise shaping). Since I don't quite understand how this works, I ...
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### The relationship between bit depth and SNR in ADC

An 8-bit audio signal has a theoretical maximum SNR of 48.16 dB (20log(2^8)). My question then would be, does this work in reverse, i.e. would an analogue audio (or video) signal with an SNR of <=...
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### Does Nyquist rate depend on the sampling rate?

The book Computer Networks by Andrew S Tanenbaum mentions the following (paraphrased): For a noiseless channel, Nyquist theorem states: Maximum data rate = $2H \space log_{2} V$ bits/sec ...
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### How do I prolong the reed switch output time

I put a reed switch ( https://en.wikipedia.org/wiki/Reed_switch ) on the handle of a measuring wheel (perambulator). The reed switch will be activated up to around 20 times per second (every 50 ms). ...
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### Can phase noise be averaged out?

I have an ADC sampling a downconverted RF signal at fs. I obtain N=2^15 samples of the RF input signal "fcarrier + fs/10". The more I average, the more the entire noise floor shifts down (as expected,...
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### Can sampling rate be a floating point number?

Suppose we have a sampling frequency for a signal of 15.5 samples/sec and we take samples for a period of 7 seconds. This means total samples are 108.5, does this make any sense? Shouldn't the ...
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### Sampling rate understanding for ADC requirement

So I have this voltage plot. These are voltages corresponding to a current changes on a wire. I am trying to understand the rate of transmission for choosing a ADC to read these analog values. The ...
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### WiFi limitations

What are the limitations of using WiFi where you have, say, 30+ clients/devices pushing compressed audio (flac)? Bitrates: ~384 to 768 kb/s (44100 x 16 x 1 to 48000 x 16 x 1) * ( 0.5 to 1.0 ) (...
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### Meaning of unevenly spaced data points in LTspice

When View --> Mark Data Points is selected on the waveform, LTspice shows data points unevenly separated along the time axis. Does anyone know what do these points correspond to? It doesn't look like ...
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### Limit of daisy-chaining of multiple ADCs

I am designing a device consisting of 20 daisy-chained ADCs (https://www.analog.com/media/en/technical-documentation/data-sheets/ad7685.pdf) communicating via SPI with the STM32F303 microprocessor. I ...
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### Sampling Theorem and reconstruction

I do not understand a concept about the Nyquist - Shannon sampling theorem. It says that it is possibile to perfectly get the original analog signal from the signal obtained by sampling if and only ...
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### Sample sine wave [duplicate]

I need to sample a sine wave in order to create a lookup table. I know the Shannon theorem but I still don't understand how to apply it. I want to have 256 discrete samples of the sine wave that will ...
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### 256-point FFT, but only need 5-6 frequencies, is there a better way?

Due to the constraints of my system, I have a 256pt FFT. However, I only care about the energy at 5 or 6 of the 256 bins. 256pt FFT is still faster than 5 or 6 specific DFTs, but it seems wasteful ...
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### Nyquist sampling rate with real and imaginary aliasing

I need to calculate the Nyquist sampling rate of the function $x(t) = cos(6t)-sin(5t)$. By definition the Nyquist sampling rate is the minimum value of $\omega_s$ that yields no aliasing ...
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I'm currently learning about Analogue to Digital Converters. From what I understand, aliasing occurs if the input signal being sampled has power above the "Nyquist frequency" of the ADC(Sampling ...
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### What should be the sampling frequency for a square pulse train in a DAQ system?

Since a square pulse has very high harmonics how to obtain a good resolution of pulses? For example if we have pulse train around 500 Hz could we treat it as a typical analog signal and sample it with ...
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