Passed through 133.45 (Clacton) sector four times last night. Had to crank the volume up to a very high level (B 737). There seemed to be a bit of 'head in dustbin' type quality to the speech. It all seemed a great performance at Swanwick when I'm sure it was a very trying time for all concerned.If we didn't know what was happening, you couldn't have guessed from the service (well apart from the speed control approaching the FIR). I hope someone sorts out the audio quality at an early stage, such a simple thing would be a big plus for flight safety.