I absolutely love how topgear edits their films and how they do the sounddesign, there is one effect however I would like to replicate but I don't know if that is even possible in post. In below videos I start the video when you hear the crowd in the stadium and that sound slowly fades out to silence, that's not a simple fade but I wonder if there is any tutorial online how to achieve this effect?

https://www.youtube.com/watch?v=OEcVusYl3y0#t=70

Can indeed be done in post ...

You need to play around with audio software. I don't know the specifics to get the effect but i'm fairly sure it can be done.

To my ear that sounds like keyframed EQ and reverb/echo effects.

When the crowd silences especially, I'm hearing a ramp down of the high frequencies. The low frequencies that are revealed seem very reverberant.

In the absence of an NLE or DAW that offers keyframing of the audio effect parameters, you would create at least two duplicate tracks. One contains the effects as you wish them at the start of the transition, the other as you wish for the end of the effect. Then you use volume envelopes to crossfade between the tracks.

Depending on the effects and transitions desired, you might need more than two tracks.

I've not seen any tutorials on this.

This "fade" is done with a lowpass/highcut filter and some reverb on the filtered signal.
So .. after the guy says "the Stig" the lowpass filter filters the frequency from 20Khz to about 120Hz in a straight line till just before scissors. A straight slope where gradually the high frequencies are filtered ending at ~120 Hz.
The reverb is mixed in at 1:16 and is max at 1:20.
Then the scissors are dubbed over, that sound is not filtered and it has it's own reverb, so it really stands out of the soundscape.
After the scissors there are sound fx and a new scene begins.
Top Gear (and BBC) deliver very fine edits indeed !
If you don't know how to actually do this, just ask :)

Thx for the responses so far, also thx for the detailed walkthrough how to achieve this effect Martijn, it does sound quite complicated to achieve though, not sure if that can be done inside Edius 7?

I found a way to make this work in Edius Noa :)
It's not what I hoped for, but you can mimic this effect with a bit of crossfading fun.
I tried to render the clip, but failed to render the audio with the video, obviously doing something wrong as an edius noob ..
I do have an infograph for you:
https://imagizer.imageshack.us/v2/1735x976q90/538/cUGXN5.jpg

First audio track is the original track, (no fx) it fades out.
Second is a copy of the first track, (low-pass 120Hz) , it fades in.
Third is a copy of the first track, (low-pass 120Hz + delay) , fades in later.

A fade in with a high-pass is also a good option to make your audio transitions more exiting.

Seth is totally right. That's how I did it.
I managed to render the video:
http://youtu.be/C1xoPi6fMhc

Thx for the edius tutorial! Will experiment some the coming weeks.

How cool is that! well done for figuring it out. I guess you can mimic the same thing in Sony Vegas too then or any other NLE pretty much.

Sony Vegas is far superior to edius when it comes to audio so I would be surprised if this would not be possible.

I have checked it out for Vegas and there you can automate all fx settings just as you can automate volume and pan in edius. So no mimicking is needed.
Vegas has no native low-pass so you have to get a 3rd party vst for that, and sony's reverb doesn't sound as good as I whish so I'll look for a better one also (freeware hopfully)
I'll probably make a tutorial on this later this week ...

Vegas Pro along with the companion program Sound Forge Pro have everything one would need for that particular effect. Audio pros (me) however, normally have lots of other free and purchased audio plug-ins as well.

I have checked it out for Vegas and there you can automate all fx settings just as you can automate volume and pan in edius. So no mimicking is needed.
Vegas has no native low-pass so you have to get a 3rd party vst for that, and sony's reverb doesn't sound as good as I whish so I'll look for a better one also (freeware hopfully)
I'll probably make a tutorial on this later this week ...

Do it, that would be awesome.

Been learning a few things this week actually (related to image rather than sound), but would love to learn audio related effects like that too on Vegas.

All the FX sends/returns can be automated in Vegas Pro, as well as all the VST plug-ins (and many DX plugs) in real-time PB by mouse, external fader surface. Also by the usual envelopes if desired. It's more complicated than the usual Vegas audio workflow though... and in typical SCS (Sony Creative Software) fashion, the manual doesn't explain the process/controls very well.

Ok, here a "tutorial" on this in vegas:
https://imagizer.imageshack.us/v2/1735x976q90/674/AF0TvJ.jpg

Result:
Low Pass Fade Vegas - YouTube

I got the free LPF filter here:
AdmiralQuality.com - Naive LPF (http://www.admiralquality.com/products/NaiveLPF/)

To put it in Vegas, copy/paste the .dll file in your plug-ins folder or make a plug-ins folder, next, in Vegas, go to Options>Preferences>VST effects. There you browse to the folder you just put it in to set it as your Default VST search folder, click refresh, and you can use it in vegas.

Amazing Martijn - thank you!