43
votes
Accepted
Why sample at a certain frequency just to immediately downsample it?
if they wanted the sampling frequency to be 10Hz, why did they not just sample at 10Hz initially?
In order to avoid aliasing, the signal has to be lowpass-filtered before sampling. No frequencies ...
- 80.3k
34
votes
When is it required or permitted to sample below Nyquist rate
First of all, let's get rid of the Nyquist rate misconception.
People are usually taught that the minimum sampling frequency needs to be twice the frequency of the highest frequency in the signal. ...
- 23.6k
29
votes
Accepted
Word or phrase to describe how frequently a value is measured
The name for the frequency the samples are taken is Sampling Rate (not specific to audio only). It is measured in samples-per-second or in Hz (which is ...
- 10.1k
25
votes
How is 10G Ethernet physically possible?
Chasing this answer down took a few different links, but it appears to boil down to this:
1. 4 differential pairs (8 wires total, but only 4 lanes).
2. 800 Mega Symbols a second.
3. Using PAM16, 16 ...
- 13k
24
votes
Accepted
Why does increasing the sampling rate make implementing an anti-aliasing filter easier?
As you decrease the sampling frequency there is less separation between the images in the frequency domain.
source
Remember that the repetition of the spectrum occurs at the sampling frequency. When ...
- 6,177
23
votes
Accepted
Can sampling rate be a floating point number?
Forget sampling rate for a few seconds... Think about sampling period for a second, which is the time interval between two consecutive samples. This time can be an integer or any real number (as long ...
- 2,237
20
votes
Word or phrase to describe how frequently a value is measured
I would call it the sampling period or measurement period. For short periods like 1 ms, specifying the sampling frequency is another option (1 kHz).
- 5,984
19
votes
Accepted
Lossless compression technique for digital signals in an embedded system
Compression is all about finding the redundancies in the data and removing them. Since you don't seem to be able to tell us much about your actual data sets, this answer will have to be very generic.
...
- 176k
19
votes
Accepted
Why do oscilloscopes list max bandwidth separate from sample rate?
The frequency given is the cut frequency of the analog input (I suppose defined at -3dB, but to be confirmed). This means that there is still some analog signal at higher frequencies, just attenuated.
...
- 7,938
18
votes
Accepted
Can the Nyquist sampling rate also apply for the human eye the same as in electronics?
The firing of neurons in the eye is completely asynchronous, so for all intents and purposes, the process we call "seeing" must be considered continuous-time, not sampled. Nyquist does not apply.
If ...
- 176k
18
votes
Accepted
What is the "Nyquist" rate for sampling the derivative of a signal?
Taking a derivative (or an integral) is a linear operation — it doesn't create any frequencies that weren't in the original signal (or remove any), it just changes their relative levels.
So the ...
- 176k
15
votes
How is 10G Ethernet physically possible?
10G ethernet (as described by other answers) does not do signal transitions at 10 GHz, it uses multiple level encoding spread across 4 pairs to achieve 10 Gb/s.
However, 10+ gigabit serial ...
- 2,559
14
votes
Can sampling rate be a floating point number?
Yes, the sampling rate can be any number you want.
But you obviously would not get partial samples in the end, you just have to round down.
In your example the first sample is taken at \$ \frac{1}{15....
- 9,679
13
votes
Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?
There's a difference between analyzing a signal for information, and displaying it on a scope screen. A scope display is basically a connect the dots, so if you had a 100 MHz sine wave sampled at 200 ...
- 60.8k
13
votes
When is it required or permitted to sample below Nyquist rate
So, many people, including professors, are confused about what Nyquist rate is:
Nyquist rate is the sample rate that you need to have to sample a signal to avoid damaging it by aliasing
What that ...
- 98.3k
13
votes
STM32F20x ADC sampling time/rate
I'll let you work out the details for your particular case, but I'd like to add some more clarity.
First off, I've opened up an errata report on RM0410 (the reference manual for my chip) here.
I'll be ...
- 1,839
13
votes
Can sampling rate be a floating point number?
Some things are always an integer. Samples are always integer. You can take 108 or 109 samples.
Sample rate can be a floating point number, or more generally a rational, or even a real.
You ...
- 171k
12
votes
Accepted
Anti-Aliasing filter design
If you are interested only in signals in the range DC to 3kHz, then only signals above 7kHz will alias onto those.
This means that you need a filter with ...
a passband to 3kHz
a transition band ...
- 171k
11
votes
Accepted
Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?
"even a simple UART samples a digital signal at the same speed..." the UART doesn't need to reconstruct the analog square wave signal that carries the digital information, so it doesn't take the ...
10
votes
Why sample at a certain frequency just to immediately downsample it?
You mentioned the word magnetometers. This expands the scope a little.
Magnetometers for those not familiar measure magnetic flux and create a proportional output voltage/ signal according to the ...
- 101
10
votes
Sampling rate understanding for ADC requirement
In order to capture all the information you need to sample at at least twice the highest frequency component in the input signal.
If you do a PSD plot of the input you'll see that there is ...
9
votes
Accepted
Meaning of unevenly spaced data points in LTspice
My guess is that these are the (time) points which the circuit simulator has actually solved.
Many analog circuit simulators, unlike simulators for digital circuits (logic), do not use a constant ...
- 81.1k
9
votes
Why does increasing the sampling rate make implementing an anti-aliasing filter easier?
To reconstruct a signal in the digital realm from the analogue realm you need at least two samples in each cycle of the highest frequency present in the analogue signal. For instance, on CDs, they use ...
- 467k
9
votes
Lossless compression technique for digital signals in an embedded system
Your data will likely have two components to it:
Low speed changes of the actual voltage
Random variation due to ADC noise
It is likely that the random variation will present most of the entropy in ...
- 9,021
9
votes
Accepted
Shannon-Nyquist - only for repeating signals?
if you decompose a signal into sinusoids, and then sample at 2x the highest frequency sinusoid, you can perfectly reproduce the original signal.
If the signal can be perfectly decomposed into ...
- 171k
9
votes
Accepted
How to achieve coherent sampling in practice
You can use a PLL (phase-locked loop) to lock the ADC sampling frequency to the input sine signal.
The bandwidth of the PLL has to be chosen to minimize the overall system's phase jitter and drift - ...
- 20.1k
8
votes
Accepted
Differences between Interrupts and sampling for hardware button?
Debouncing is a FAQ. You should be able to find... nearly unlimited numbers of web pages on the topic. Smith commented about Jack Ganssle's widely read PDF on the topic, as well. And with all these ...
- 78.4k
8
votes
When is it required or permitted to sample below Nyquist rate
Never. But you need to make sure you understand exactly what the "Nyquist rate" actually is.
Nyquist stated that you you can reconstruct the signal as long it is sampled at a rate that is more than ...
- 176k
8
votes
Is there an efficient way for synchronising audio events real-time with LEDs using an MCU?
I am not fond of encoding command data as an analog signal in a digital file.
I think I would try something like encoding the lighting commands as text blocks in the lyrics block of the ID3 ...
- 73k
Only top scored, non community-wiki answers of a minimum length are eligible