A380 Noisy?
 

Beautiful clear cold day gave me a great view of AF A380 heading west over Camberley today pretty much dead on 1400 no contrails compared the Ryanair just ahead of it but quite lot of noise-a soft roaring is how I would describe it almost like a pre fan engine jet.
Question is-did I hear the Airbus, which whenI have seen close up at LHR seems quiet, or was there say an RAF VC10 outbound from Brize that I couldnt see but could hear (and often do).
It did really appear to be from the big Airbus but does sound carry more in todays clear cold air(my physics was never good enough) because it certainlyseemed to make much more noise than the average overflight.
Just curious -mind you there was an extraordinary amount visible in the little space constituting PB airspace at the same time- as well as the two aformentioned there were two in trail LH bound airbus 320s downwind for the LHR 09s and a north to south rear engined twin jet also contrailing.

High altitude traffic does seem a bit noisier on cold days - think there was a discussion about it on here a couple of years ago. From memory it was when we had that sudden snowy burst in early February 2009.

I've heard the Antonov Mryia 225 6 can affair transit, at cruising Alt. over us before I could see it through some bins.
The A380 is just as audible due, I would surmise, to the output of those massive fans.
The larger aircraft seem to have a 'compressor' type of sound over the raucous sound of a 'lesser' jet.

It's all to do with Doppler shift, wave compression, air density and M number reduced to speed in metres/sec and it's very complicated. Unfortunately human hearing really only operates on one pulse repetition frequency (PRF) which causes ambiguities.
I would say therefore that a reasonable off hand explanation for some one who is not an aeronautical engineer would be that it's all due to variations of air compressibility at altitude brought about by the extreme cold air bearing in mind that at ISA - 15c at sea level, calaculate the ISA temperature at say 20,000ft.
Toodle pip?