It’s a mixed bag. Forza 4 definitely had much better audio adjustments,
you could even set the focus towards your engine, or tires.
Then there are certain cars in Forza 5, that I just can’t enjoy anymore, because the sound sample hurts my ears.
The '95 Cobra does not have the throaty V8 sound it used to have in previous titles, it’s too high pitched.
The older Mitsu Evo also has a distortion in the sample.
Despite all that, the overall audio quality is much higher in FM5.