Interference describes the loudness of the instruments compared to the loudness of the vocals. For example, ‘strong interference’ indicates a strong contribution from other instruments, whereas ‘no interference’ means that you can only hear the vocals.
Interference does not include artefacts or distortions that you may perceive.
All of these have no interference from other instruments despite the sound quality being different
In this example the amount of interference is changed by varying the relative loudness of the backing instruments