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I'm trying to design a relatively simple (electronic) device for obscuring/jamming voice recordings with a laptop microphone. I've read that playing white noises in the background doesn't mask over voice so effectively, unless the gain is fairly high. Does anyone know what might be a better option?
Any thought appreciated.
There are four obvious options:
Use an incredibly loud noise which maxes out the laptop mic, effectively giving you a square wave where the signal you are trying to mask is undetectable. This does mean you are having to talk in that loud environment. Maybe not ideal...
Instead of high amplitude audio waves, you could go for high intensity electromagnetic waves targeted on the mic. Realistically this is probably as likely to fry your laptop as obscure sound, so it may also end badly.
Your electronic device (if you are allowed access to the laptop) could simply break the circuit to the mic, thus rendering it unable to pick up anything.
Take the laptop away and place it in a separate room.
Okay, the last one is a bit tongue in cheek, but it works.
You may have success with some kind of pistonphone:
It's a device that provides a known sound pressure level (typically 114 dB SPL) that's used to calibrate measurement microphones. In order to achieve that SPL, the microphone has to be inserted into the pressure chamber of the pistonphone (opening at the top of the device, see image) where the microphone's membrane couples with the volume of air inside the chamber—the air is moved by a piston which creates the necessary pressure. Outside the chamber, no sound coming from the device is audible.
Now, you most likely would have to build something similar yourself. Since for your purpose you don't rely on anything being exact, you could try to just follow the key factors in play here: very close proximity of sound source (sound pressure source) and microphone membrane and a closed chamber. If you know exactly where the microphone sits in your machine and if you can access it, it shouldn't be too hard to build some kind of jammer. I assume that even something as simple as a cap housing a piezoelectronic speaker that fits on the microphone might give the results you are looking for. Basically the goal would be to distort every recording in a way that is beyond recoverable, like Rory Alsop mentioned in their answer (bullet point 1) without having to deal with speakers blasting a masking signal—that's mostly necessary when you don't know the location of a potential bug.
