Loaded ProTools 8.0 into a laptop for a mobile recording unit. Using an M-Audio MobilPre USB as an A/D converter. USB into the converter, connected to the laptop. Plugged the dongle that came with the ProTools into another available USB port on the laptop. It records guitar or keyboard, but only if the volume control for the input on the A/D converter is maxxed, which is accompanied by a corresponding increase in b ackground hum that sounds like a 60Hz sidetone. The ProTools works fine on my desk top unit through an M-Audio 2696 interface. I got the MobilePre second hand from someone who was moving-could the age of that unit be the problem?
low recording level with sidetone
4 Answers
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Well, so you at least get a better answer from us, I'll assume you may have a ground issue, generally a good DI with a ground lift will get rid of those 60/50Hz cycles.
I'm going to recommend this DI to you:
http://www.sweetwater.com/store/detail/ProDI/
I can guarantee that 60Hz is still there, just attenuated now, the DI will solve the issue.
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Have you swapped out all cables or looked for anything that could be causing interference?
What is your cable setuP
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How are you recording? XLR + mic or instrument input? Need more specifics to help you solve this.
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Thank you to all who responded. When I amplified the signal from the instrument the recording level on the A/D converter could be reduced to a managable level which reduced the 60Hz hum-obvious, now that I look at it.
Astral Plane Studios 
Eekamouse Not the answers you're looking for? Try asking your own question.
Have you managed to solve the problem yet?
Astral Plane Studios | Dec 18 at 04:12