Even with sound muted, running Matlab makes high frequency sound in my earbuds. What's going on?

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Greg
Greg 2016-10-24
评论： Walter Roberson 2016-10-25
Running Matlab commands creates a high frequency, modulated noise in any headphones/earbuds plugged into my laptop. The noise lasts as long as the commands are running, i.e. for as long as "Busy" is showing in the bottom left of the Matlab window. This occurs even if the sound on my computer is muted. Without headphones I can't hear it (either too quiet or not occurring). It's a little weird.
I have a MacBook pro, OSX 10.11.3, and I'm running Matlab 2016a. This (non-)issue also occurs for different Matlab and OSX version, but only on my laptop, i.e. not on other hardware.
This is a strange question, and it likely has more to do with my hardware than Matlab, but it's been happening for a while and I'm curious if anyone knows what's going on!
edit: No other software does this, just Matlab.

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Walter Roberson
Walter Roberson 2016-10-25
You are getting radio frequency noise when MATLAB is doing some operations.
Does it occur even for simple activity such as
pause
or simple loops
for K = 1 : 200000; end
? Or does it only occur when math operations are happening?
If it happens when math operations are happening then the interference might have to do with use of multiple CPUs: there are some kinds of math operations for which MATLAB automatically uses multiple CPUs once the arrays involved are "big enough".
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Greg
Greg 2016-10-25
Thanks. Interesting! I'm guessing from your answer that this is a known thing, but a quick google search doesn't show anything. Can you point me to anything that explains it in more detail?
And you're correct that it only happens for operations that seem computationally heavy, e.g. it does not occur for the two examples you gave.
Walter Roberson
Walter Roberson 2016-10-25
This is not specific to MATLAB at all. It is the same reason why my (landline) phone gets noisy when I lean too close to my computer while I am talking on the phone -- EMI, Electro Magnetic Interference. See for example https://en.wikipedia.org/wiki/Electromagnetic_interference#EMI_in_integrated_circuits
When you use your headphones plugged into the laptop, you are adding a conductive cable that extends to inside your laptop. The cable can act as an antenna; the fact that the plug extends inside the laptop reduces the shielding provided by the computer case.
I do not observe the same effect on my MacBook Pro, which is probably a different model than yours (mine is the last of the non-Retina series, as they offered both the first year that Retina came out.) Also, if your laptop is damaged the the shielding could be reduced.
There are a few possibilities here:
  1. that the particular model you have was designed with inadequate noise shielding for the earphone
  2. that some defect or misalignment of parts or damage has resulted in increased EMI being generated beyond the limits that the shielding was designed for
  3. that some defect or misalignment of parts or damage has resulted in normal EMI levels but the shielding being worse than designed for
We cannot tell the difference between these possibilities: they are all hardware problems and call for hardware testing.

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