more quiet ion engine sound

src/actor.rs

@@ -859,11 +859,13 @@ fn handle_wants_acceleration(
             }
 
             if accel.direction != DVec3::ZERO {
-                // Player is pressing AWSD keys
+                // Player is pressing AWSD keys.
+                // When braking AND accelerating, boost acceleration a bit to
+                // overcome the braking and cause a slow acceleration:
                 let brake_factor = if accel.brake { 1.10 } else { 1.0 };
                 delta_v += accel.direction.normalize() * brake_factor;
             } else if accel.brake {
-                // Player is only pressing space
+                // Player is only pressing space.
                 allow_fullstop = true;
             }
 
@@ -955,7 +957,7 @@ fn handle_wants_acceleration(
             sinks.get(&audio::Sfx::Thruster),
         ),
         (
-            1.0,
+            0.6,
             1.0,
             actor::EngineType::Ion,
             sinks.get(&audio::Sfx::Ion),