Ryszard,

One of the reasons I got rid of my PreSonus Firebox (basically a firewire version of your Audiobox) is that there was two internal signal issues with it - which turned out to be somewhat common after perusing their support forums:

1. Signal bleed from headphone output (no mics being used) into the input channels. I never realized it was an issue until final mix-down of a song that I blew through in a day. Here's the song: https://soundcloud.com/rockstar_not/scott-lake-rest-ye-orion listen to the very tail end of the song. If you turn up the playback enough, you'll hear my click-track. No microphones were used in the recording process

2. The second issue was that there was a very high pitched whine on the input pre-amps, when turned up to the last 20% or so of gain. Again, an issue that I found out was common through the threads, but after my warranty period expired. I would estimate the frequency at 8kHz or above.

I no longer have that device - I sold it after my fire-wire equipped lappy went south permanently.

I hope that your situation is not the same and that you simply have some grounding issues to contend with.

Other sources of whine to be mindful of:

1. Some laptops LCD backlight is controlled by a pulse-width-modulated control circuit which can induce whine over the USB. We had some Thinkpad T-series laptops at work which exhibited this issue.

2. Other stuff on your USB - try to eliminate as much off of the USB as possible, including any powered ports. The power supplies on those are usually crappy switching jobs, and they can make headaches for noise on the supply of the USB, which depending on how well the audio interface is designed to reject incoming noise on the USB, may cause issues.

-Scott

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