On Sat, Jul 04, 2020 at 07:13:15PM +0100, Bev Nicolson wrote:
By the way - by 'hum' you do mean mains hum do you? I.e. a very low
frequency hum of fixed frequency.
Hopefully this short audio clip will explain the hum. I don't hear it as I record anything, but only on play back.
That's mains hum. Because of the way it sounds, not a 50Hz sine wave, rather a 100Hz 'buzz', its source is probably imperfect smoothing (as in electrical smoothing) on a power supply somewhere.
I have headphones and a mouse plugged in, to answer your other query, but if anything it's worse without the headphones.
OK, it probably just sounds worse without the headphones because you can hear it 'better' on the laptop's speakers.
Have you made a recording with everything unplugged? If you go out in the garden (well, away from anything electrical anyway) and make a recording using the internal microphone and play it back out there too do you *still* get the hum? I'd be surprised if you do.
Having got a 'clean' recording you should then be able to workout exactly what stage is adding the mains hum.