Hiss In my system : Where does it come from?

[xaccrocheur]

Hi everyone

My audio interface is a M-Audio fasttrack pro, and it works pretty good (no additional driver, just usb-audio I guess) but there is a high-pitched hiss that makes me crazy.

As far as I can tell, it's only a monitoring problem, and the hiss is not on the tape.

The thing is, it only turns on (the hiss) when Jack switches on, not before, although everything is already plugged in..? What I tried:

- Plugging a PSU it it, but not connected to the wall, as 1-I don't have the interface power brick, and 2-I don't think this room's wall outlet are earthed. It changed nothing and it's quite telling: If it were a grounding problem I should at least hear something when moving the power cable, nothing.
- Playing with logical / Jack connections : Nothing.

The hiss is solid, undisturbed by anything, turning all the output volumes off on the interface does *nothing*.

By posting this I only hope that it sounds like something somebody experienced, and hopefully fixed ; thanks for your patience.

[bluebell]

Hi everyone

My audio interface is a M-Audio fasttrack pro, and it works pretty good (no additional driver, just usb-audio I guess) but there is a high-pitched hiss that makes me crazy.

As far as I can tell, it's only a monitoring problem, and the hiss is not on the tape.

The thing is, it only turns on (the hiss) when Jack switches on, not before, although everything is already plugged in..? What I tried:

- Plugging a PSU it it, but not connected to the wall, as 1-I don't have the interface power brick, and 2-I don't think this room's wall outlet are earthed. It changed nothing and it's quite telling: If it were a grounding problem I should at least hear something when moving the power cable, nothing.
- Playing with logical / Jack connections : Nothing.

The hiss is solid, undisturbed by anything, turning all the output volumes off on the interface does *nothing*.

By posting this I only hope that it sounds like something somebody experienced, and hopefully fixed ; thanks for your patience.

Do you have several devices connected that have a power plug with protective ground? And do you connect the audio interface and other devices (mixer, active speakers, amp) with a non-balanced cable?

This is alwaysa good recipe to get hum and/or hiss.

[xaccrocheur]

Sounds like I have at least one of those things thanks a lot for your response.

When you say "several devices connected" what do you mean exactly? On the (electrical) wall outlet, the (audio) interface, the (usb) PC..? About the (un)balanced cables, clearly yes, I just use cinch / RCA stereo cables to go from my interface to my amp, then a basic two-wires "insulated audio" (yeah, right) cable from my amp to my (passive) speakers ; should I use something else?

Bonus Q: Do you think I can get away with an ungrounded system / studio?

[bluebell]

Sounds like I have at least one of those things

When you say "several devices connected" what do you mean exactly? On the (electrical) wall outlet, the (audio) interface, the (usb) PC..? About the (un)balanced cables, clearly yes, I juste use cinch / RCA stereo cables to go from my interface to my amp, than a basic two-wires "insulated audio" (yeah, right) cable from my amp to my (passive) speakers ; should I use something else?

To get an audible ground loop you need:
- at least 2 devices with a plug in the wall outlet that has a protective earth
- at least one unbalanced audio connection between those devices (cinch/RCA or TS jack)

Code: Select all

PC ---- audio cable's shield ---- active Speakers
 |                                    |
 +--Ground----------------------------+

The Loop

- "PC" can stand for "PC with USB audio interface" as well
- "active speakers" can stand for your amp with passive speakers as well

The cable from the amp to the passive speakers plays no role regarding a ground loop.

If you have a HiFi amp that has only unbalanced inputs (cinch) then you are screwed. Sometimes a 1:1 transformer helps because it cuts the ground loop. See https://www.oehlbach.com/de/audio-equip ... o-linear-8