Analog vs Digital

Analog servos only produce full torque when nearing their commanded position. Digital servos produce full torque at all times, thats why they hold better and stay centered or stay where you tell them to go during high stress manuevers.

While the servo gets its position update at 50hz from the reciever, the analog servo updates the motor position at that rate.

With a digital servo, the digital amplifier updates the servo motor at 270 to 300 times per second which is why its always producing full torque (and the reason they buzz at rest with even the weight of a control surface on them). The downside of course is that this motor updating consumes power so they use more Mah than standard servos.