<Slider Ticks="1, 2, 3, 4, 5, 6, 7, 8, 9, 10"
Value="1"
Delay="100"
Interval="5"
TickPlacement="BottomRight"
Minimum="1"
Maximum="10"
Width="100"
AutoToolTipPlacement="BottomRight"
ValueChanged="slider_ValueChanged"
Grid.Row="1"
Grid.Column="0">
Slider>
создать событие slider_ValueChanged
и установить Speech.volume = (int)sliderID.value;