Old 07-15-2017, 02:31 AM   #1
eisenfarn
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Default Reaper Hum Loop?

Hi, I'm using Reaper on a HP laptop connected via USB to a Focusrite 4i2 (second generation). All was well until I had a problem with the hard drive and had to reinstall Reaper and the Focusrite drivers. I can connect the laptop to the Focusrite and then to the PA system, but as soon as I start Reaper, I get a hum and a kind of swirling phasing sound through the PA, close Reaper and the sound goes away, If I disconnect the laptop from the power supply, even with Reaper running, the sound also goes away. Has anybody come across this before?, thanks
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Old 07-16-2017, 01:11 PM   #2
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This is a well-known and fairly common problem with laptop[ power supplies. I suspect you will find that just about any audio software will have the same issue with your laptop when it is plugged into the mains. The solution is either get a better quality power supply for the laptop which MIGHT fix it or more pragmatically, get 2 batteries if you don't have time for a quick top-up charge between sets.

Since I got a SSD in my laptop I get about 6 hours, so it shouldn't be too difficult for ya
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Old 07-16-2017, 07:09 PM   #3
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Use a ground lift box between the focusrite stereo outs and the amplifier/mixer/whatever comes first in your PA system.

You have a loop like so:

house power > power cable > computer > focusrite > PA system > PA power > house power

If you can't do a ground lift, use batteries.

The swirling sound is capacitor flux (that sounds more complex than it is ), changing the frequency of discharge which you are hearing because the noise/tones generated in a ground loop are the result of an electrical signal being converted to sound by speakers.

Another thing that may work but is expensive is to purchase an isolation transformer box for the wall plug. Power either the computer or the PA from that and you've broken the loop.
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Old 07-17-2017, 04:04 AM   #4
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Thanks guys, but it seems odd that I never used to have this problem, and it only happens when I start Reaper on the laptop.
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Old 07-18-2017, 01:33 AM   #5
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Is reaper the only DAW you have tried on the laptop?
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