From MP3Car.com Wiki
This information applies to version 1.1.0.2 and later of StreetDeck.
[edit] About Navigation Voice Prompts
When the vehicle is coming up to a turn and there is an instruction to be spoken, StreetDeck will prompt with spoken directions up to 3 times before the turn. The first prompt will be spoken as Prepare to <Turn Type>, the second as In <Distance>, <Turn Type>, onto <Street Name>, and finally right before the turn, Turn Type. The maximum number of directions that will be spoken can be configured in navigation settings through the option titled Voice guidance should be given when. If Before the turn only is chosen, only the second prompt will be given.
The distance at which the first voice prompt for the next turn will be spoken depends on the maximum speed traveled on the current route segment according to the following table:
Speed > 61 = .9 miles
Speed > 30 = .5 miles
Speed <= 30 = .25 miles
The distance for the second voice prompt will be at .57 times the distance the first direction is spoken at.
The distance for the third voice prompt will be at .1 times the distance the first direction is spoken at.
[edit] Modifying the distance at which prompts are spoken
To change the distance at which the next voice prompt is spoken at, the command line parameter NAVSpeakDelay can be used followed by a real number that will multiply the distance at which the voice prompt is spoken at.
For example, -NAVSpeakDelay:2.5 will multiply the the distance by 2.5. This will make the distance when the speed > 61 .9*2.5= 2.25 miles, the distance when the speed > 30 = .5*2.5=1.25 miles, and the distance when the speed <= 30=.25*2.5=.625 miles.
