-> 1. The volume Slider
-> 2. The Launcher Settings
-> 3. How to make a custom engine sound
-> 1. First of all : The volume Slider
I'm gonna first explain how it works with ShootMania :
10/10 white dots : At full range you have the "Loud Mix". Loud Mix has less volume attenuation by distance (rolloff). Also the rocket trails, the rocket explosions, and your own footsteps/jump sounds are louder.
7.5/10 white dots : At these point you've reached the Quiet Mix. The Quiet Mix was made for 2 purpose : people that want to play loud FFA mods in a calmer in-game sound environnement, and competitive players that wants to play mods like elite or joust with a less messy sound (but also less fun

Between 7.5 and 10 : You make you own compromise between the 2 mix.
Below 7.5 : You're reducing the main volume, it start acting like a regular volume fader, but using the Quiet Mix only.
About TrackMania :
This feature also exist in TrackMania Stadium, the quiet mix reduce the engine sound volume, to play easily with music (the continuous sound of the engine ruins the music), keeping the most important sounds like UI, Hits, Skids, Sound of the texture you're on etc.
SO IF YOU FIND THE ENGINE NOT LOUD ENOUGH MAKE SURE YOUR VOLUME SLIDER IS SET TO THE MAXIMUM
In Canyon, at the moment, the volume slider works as a normal volume slider, from 10 dots to 0. It will work like Stadium's volume slider in maniaplanet's next update.
-> 2. The ManiaPlanet Launcher Audio Settings :
Sound Quality : SET IT TO NORMAL ONLY !
This setting determines the maximum number of simultaneous sounds played while playing. Normal is 32, High is 48 (Low is something like 10..).
Low and High quality are bugged and do not work properly (at least for some people). If you are using high quality and you don't see anything wrong, do not panic it's probably working well.
BUT, i strongly advise all of you to chose Normal quality ! It is the optimal quality, in terms of performance, but also in terms of clearness, having more sound than 32 is just messy in my opinon, and you can't really tell the difference.
Don't ask me why you're able chose, just set it to normal.
Enable EFX : EFX are some effects applied to the in-game sounds. Mainly it is the reverb, and the high frequencies attenuation due to distance. Those two effects are part of the parameters that help for a better distance appreciation of the sound source, so it helps for a better general localisation of your enemies.
I do strongly advise you to enable it, except if you are having big troubles with it, in this case, please post about it in the forum with a video+sound attached to your report.
Enable HRTF : This is supposed to enhance the sound localisation like hearing if the sound comes from higher or lower (you can not localise verticaly without it). The thing is, it's working too agressively (if you enable it you mostly
destroy the sound quality, and it makes your head spin so hard... quite confusing at first). I hope time we'll be on our side to someday make this work properly, but as it is right now, it's up to you to use it or not, i personally don't. The game's sound was never mixed or worked with this feature so use it at your own risks if you really want to use it..
Enable Dynamic Mix : This option is not really relevant anymore, it was supposed to bring up the volume of every quiet sound, when not much was going on. Let's say it was a sort of compressor reducing the sound dynamic of the game. But it was not really working well, and quitte messing up the sounds localisation.
It's acting very discreet now, so you won't notice much difference enabling it. I have it turned off, let's say it's up to you.
Enable doppler : I don't even know why you would disable doppler, if you don't know what is the doppler effect type it on google, but without it the rocket trails would be quite weird and boring hehe.
Conclusion, don't pay any attention to it and keep it enable.
-> 3. Custom Car Sound :
N.B : Regarding Stadium, there is a bug at the moment, preventing you from using custom car sound, it will be fixed in next update, sorry about that, but you'll be able to use it pretty soon !
For those needing help on how to make custom engine sounds, here's how it works :
It requires several engine sound loops, at different RPM, and taking into account the RPM value that you fill in your filename, it will pitch the loops to make them match during the transition between two loops.
So if you want an engine to sound good you should fill in the right value, or at least proportionnal values (that sometimes, can be a bit complicated...).
Let's say you have a loop at 2500Rpm and another one at 5000Rpm, even if they are not exactly at 2500 and 5000Rpm, the main frequency from loop5000rpm has to be twice the loop2500Rpm's main frequency. And so on.
If remember correctly in TM²Stadium Rpm goes from 75 (idle) to 11000 (full range, switch gear). But in Canyon (And Valley) it goes from 2500Rpm (idle) to 11000Rpm.
A way to manage to make loops match between each other could be by starting with your "reference loop", let's say the lowest-pitched one (for example 2500Rpm).
1. Drag&drop it to Audacity, and drop the next one also (5000Rpm).
2. Listen to both in the same time, then change the 5000rpm sound's pitch, so that the 2 files sound in tunes, like in a musical way, the same note but an octave higher. (In audacity don't use "Change Pitch" but "Change Speed", it's the same except that change speed is more accurate).
3. Here are two loops working fine together

It get's more complicated if you want to add a loop in between, like 7500, that is 1.5 times 5000 and not 2 times like the previous example. You can do it by :
1. Pitching this next loop so it matches 10000Rpm.
2. Writing down the percentage of "speed modification" you had to use to make it work.
3. And then do some simple math to find the right percentage for the desired value (here 7500Rpm).
4. Use this percentage to edit the original file ! Don't try to go backward on an already pitched file, it will ruin it.
Yes that sounds like a lot of work, but this is the complicated way to make a really clean engine sound. Though, an approximative engine sound, without all those complicated stuffs, can also work, the most important thing is the sound itself (needs to be fun to race with

You can create many loops and fill in their filename with what the loop is about :
loop_("xxxxx")Rpm_("throttle" or "release")_("engine", "exhaust" or "body")
example : loop_11000Rpm_throttle_engine.wav
"body" is supposed to be the engine sound inside the car, right now in Stadium (and only in stadium), it's used for the engine "bass" sound, so i guess it will not be working perfectly as a "body engine sound".
I'll let you know if there are any evolutions on this matter.
Engine audio loops file format have to be *.wav or *.ogg. Put them all in a folder and name it "Engine" (YourSkin.zip\Engine). Regarding custom horns, they have to be at the zip's root (YourSkin.zip\Horn.wav).
Finally, place your custom TM Stadium car skin here : Documents\Maniaplanet\Skins\Vehicles\StadiumCar\.