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@General Lighting 454217 wrote:
I’ve just spent nearly hours sorting out a noise/grounding issue (was testing to see if I could record sound / stream from another computer). Tried every combination of sound cards, USB leads/hubs etc – and I haven’t got the kit to make up balanced cables and not all my kit is balanced anyway….turns out that the mains PSU is the source of it but the machine I was going to use for this is a old laptop with a fucked battery so it has to be plugged in.
Managed to solve it by using a even older machine to deal with the incoming audio, but it turns out that newer laptop PSU’s with a 3 pin mains connector send all manner of crap and noise down the mains earth and because of safety rules this ends up on the audio signal earth as they are normally connected together…
Yep I’ve had this exact problem before when doing the sound for a show at the film and comic con for my mate at earls court last year.
He was advertising his pc game he was making at the time and using a laptop hooked upto a big monitor and speakers, but the battery lasted about 20-30 mins tops so we had to have it plugged in and the ground loop it created was horendous! We actualy had to have no sound 90% of the day and even fucked up a showing to alien ware cos the battery had just died as they came past and we were too embarised to show it with the sound like it was.
External soundcards go someway to fixing it aparently (alltho i have a feeling this just gets rid of some extra noise caused by components inside the laptop /pc getting picked up by the soundcard due to electromagnetic waves rather then from the power suply ground loop), idealy tho you want all your sound equiipment (anything that carries an analoug signal thru it) like speakers etc on a seperat isolated circit to stuff like pc’s/lap tops.