_slave->speed_and_position (slave_speed, slave_transport_frame);
DEBUG_TRACE (DEBUG::Slave, string_compose ("Slave position %1 speed %2\n", slave_transport_frame, slave_speed));
_slave->speed_and_position (slave_speed, slave_transport_frame);
DEBUG_TRACE (DEBUG::Slave, string_compose ("Slave position %1 speed %2\n", slave_transport_frame, slave_speed));