The MMX 2 and in particular the MMX 300 are characterised by their unaltered and low-distortion transmission. However, the voice quality that can be achieved also depends on the audio codecs used in game consoles. These are usually dynamically adjusted to the available bandwidth.
Voice transmission is therefore adversely affected when there is a slow or unstable Internet connection. In a nutshell: If the voice transmission quality is unsatisfactory, this is generally not due to the headset.