when having PSR-SX900's USB-midi connected to a computer and audio (balanced) outs connected to audio interface (mackie onyx producer 2x2) there is usb noise on the audio inputs and outputs.
the noise also gets recorded onto the audio track.
using unbalanced audio cables its much louder but using balanced its quieter but still audible.
Hi kampot,
first of all, you should use unbalanced (TS) Audio cables only with the SX900. This is because all Audio outputs and inputs are unbalanced TS jacks. If you use balanced (TRS) cables, your Audio interface will receive the plus-phase signal only. The "Ring" contact (on which the Audio interface expects the - phase signal) is not connected inside the SX output jacks. This can cause hum, and the effective incoming signal level on the Audio interface is relatively low, because no minus-phase signal is received.
So, either use unbalanced TS cables or, if using TRS cables, the Ring and Sleeve contacts must me bridged (to get unbalanced cables again).
If relatively long Audio cables (over 3 meters) are needed, I recommend to use a Stereo DI Box (short unbalanced TS cables from the SX900 to the DI Box, and then balanced XLR cables to the Audio interface).
Regarding "USB Noise": In principle, USB is a digital Interface, and this cannot actually produce any noise. However, it can happen that disturbing (usually high-frequency) audio noises get from the computer to the keyboard via the ground connection of the USB cable.
These noises often come from the (switching) power supply of the computer. If you are using a Laptop, please unplug the power adapter to test whether the noise transmitted via the USB cable then disappears.
Another option would be to use a USB Isolator box (to break the direct ground connection between the computer and keyboard).
Hope this helps!
Best regards,
Chris