Hot answers tagged noise
11
The human ear responds only to the intensity $I$ of the sound it receives (more specifically, to the intensity distribution over the different frequencies) and this goes more or less like the square of the amplitude,
$$I\sim A^2.$$
Changing the sign of the waveform changes the sign of $A$, which has no effect on $I$.
7
Re your last question: what you've achieved is essentially the same as if you wire one of your speakers the wrong way round so it moves in antiphase to the other speaker. In principle there will be points equidistant from both speakers where the sound waves cancel and you get a quiet spot. However as soon as you move closer to one speaker than the other you ...
6
The key to this is the physical principle that the quantity you're asking about (delay between noise and noise cancelling) carries dimensional information (i.e. it's a time) and therefore it has to depend on the specific situation.
The simplest case is trying to cancel out a pure note, with a sinusoidal waveform, then the delay can be as long as you want: ...
5
Treating the signals as time series: If the first signal $S_1$ has a noise component $N_1$ added to it, then the noisy signal is $S_1+N_1$, similarly the second signal is $S_2+N_2$, so the difference signal would be $(S_1+N_1)-(S_2+N_2)$ and its signal to noise ratio would be $\langle(S_1-S_2)^2\rangle\over\langle(N_1-N_2)^2\rangle$
If the signals are ...
5
The threshold theorem says that if the error rate is below the threshold, a quantum algorithm with T locations (breadth times depth) can be made fault-tolerant with a blow-up (in both number of qubits and circuit size) by a factor which is a polynomial in the log of T. This is not enough to change BQP.
4
I didn't see the episode, but it may be referring to "Phreaking", by which the signals from a CRT monitor can be listened-in on (it uses high frequency changing currents to display the information, so these will inevitably result in some RF radiation from which this information can in principle be extracted).
Wikipedia article has a bit more info.
3
It seems that the confusion is due to some unfortunate notation. As the OP states, Fano noise is due to the variance in photoelectron production per incident photon, and this should indeed be signal-dependent. However, the author also states that the total noise is given by:
$$\tag{1}
\sigma^2_\mathrm{TOTAL} = \sigma^2_\mathrm{READ} + \eta_i F_F + \eta_i S
...
3
First, dB means nothing by itself. You need to give a reference level, like dBW or dB SPL. We'll assume dB SPL.
Second, noise measurements from a point source like this require a distance measurement to be meaningful, since the level drops off with distance. We'll assume you're measuring at the same distance in both cases, and the fans are equidistant ...
2
Mechanical noise is a form of energy loss, which ultimately also will end as heat: the acoustic waves will be absorbed by different kinds of substances which will vibrate more causing friction which will ultimately cause a temperature rise.
Note that the acoustic power is often extremely low, often no more than a few mW, and when those get absorbed by a ...
2
I'm no ANC expert but I'm pretty sure the limit you're talking about would have something to do with the Haas effect (also called precedence effect).
from Everest's Master Handbook of Acoustics:
"...Haas found that in the 5 to 35 msec delay range the sound from the delayed loudspeaker has to be increased more than 10dB over the direct before it ...
1
There are different sources of noise, and many different contexts that noise occurs, and when one says there is, "no such thing as a perfect one-way valve", one needs to be more specific about the particular context one is referring to. If one uses a one way valve where the input is a high pressure system, and the valve is isolating the high pressure from ...
1
In statistical mechanics and thermodynamics you are describing systems with an extremely large number of possible variables or degrees of freedom, so describing EXACTLY what happens becomes impossible. Instead, you describe the average. To do this, you consider all physically possible configurations of your system, and say they are all equally probable. ...
1
Mechanical friction is a perfectly fine example. The coefficient of friction between two materials does not approach zero at absolute zero.
Electrical resistance (as pointed out by Alexander) is another example. Some materials (superconductors) have zero resistance at absolute zero, but by no means all of them!
I would say that $\gamma \neq 0$ while $T=0$ ...
1
The way I would approach this is to consider blackbody radiation, where a spherical blackbody radiator is isotropic, e.g. it emits radiation equally in all directions. If we were to model the noise introduced by such a blackbody, it would be additive Gaussian white noise. In this example, it is called white noise because it has a flat power spectrum ...
1
The noise may have no preferred direction, but for large enough volumes the average
$$\langle\mathbf{F}\rangle_V=\frac{1}{V}\int_V \mathbf{F}(x) d^3x$$ will approach the constant term. Thus the field is not isotropic and there is a preferred direction: that of averages over sufficiently large volumes. (Here, of course, specifying the direction to arbitrary ...
1
OK, a little bit like zephyr's answer, I started with white noise, took the FFT, and then scaled each frequency component up or down according to the square-root of the power at that frequency, then did inverse-FFT to get the time-domain signal.
An equivalent approach would have been to generate the FFT directly by giving each component the appropriate ...
1
From your description of the experiment (please correct me if my assumptions are wrong), it sounds like your apparatus consists of the application of a controlled stress to the sample (and the sensor), and the resulting strain in the sensor is measured. Whenever the stress applied by your apparatus changes, it will take some time for the system to settle to ...
1
10 decibels means ten times the power density of sound. That is chosen so that ten decibels equals one bel, and a one bel increase simply adds a zero on the end of the sound power density. Twenty decibels multiplies by 10 twice, so twenty decibels is an overall 100-fold increase in the sound.
That means one decibel multiplies the sound by the smaller ...
1
The terms "white noise" and "pink noise" are applied to noise that depends on a parameter. The equation you gave technically isn't noise at all--- it's a real number uniformly distributed between -1 and 1. But I will assume that you are calling the RAND function inside a routine, and that this routine is simulating some system in time, and every time step it ...
1
For pink noise, the power spectrum falls off as 1/f. Remember that power is amplitude squared. For an electrical signal, power is voltage across times current flowing through a load, and the current follows from Ohm's Law. It is possible to arrange resistors and capacitors as a low pass filter to make an approximation of pink noise, but it's not precise. ...
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