What is a ground loop in audio systems?
A ground loop can occur when the grounds of multiple devices are interconnected. In such a system, if a voltage difference occurs, for example, due to a higher power consumption of one device, it can cause ground level fluctuations for other devices. As a result, from the perspective of a single device, a variable reference voltage appears, leading to an analog signal. Devices such as mixers, amplifiers, and audio interfaces, being precision measurement equipment, reproduce this signal exactly as it occurs, which our ears can easily detect.
What does a ground loop sound like?
Recorded noise at the speaker output in a ground loop system (DAC connected directly to PC)
Recording noise at the speaker output in a system without ground loops (via the connected A2circuits isoUSB+ isolator)
Depending on the cause of the ground loop, you may also hear mains hum, or other phenomena that are temporally correlated with changing power consumption, such as activity from the PC's graphics card (GPU).
Solving the ground loop problem in digital systems
The hissing noise heard above is closely related to digital interference conducted through the ground loop. Popular solutions to this problem, such as connecting all devices to a common outlet, did not resolve the issue in this case.
The solution that is absolutely not recommended This is a break in the grounding (protective conductor), often called a "ground lift." Such actions expose a person to electric shock if high voltage penetrates the housing!
For this reason, the recommended solution is to use a USB isolator. This approach provides protective grounding, for example, to the device's enclosure. Furthermore, a USB isolator provides 1500 V or more of isolation voltage, which can protect your device in the event of a short circuit or electrical discharge.
Difference after ground loop isolation
The graph below shows the noise spectrum before connecting the USB isolator for the audio interface. (blue color) and after (yellow color) .
In the measured range covering the 80 kHz band, a noise reduction of 32 dB is visible, as a result of which the noise level in the system was reduced to natural.
Please note that audio interfaces require high-speed isolators that support 480 Mbps. Most cheap isolators only support 12 Mbps - USB Full
