A blowing lance for refining metals by blowing a gas onto a surface of a metal bath is presented. This lance has an adjustable tuyere for generating a supersonic refining gas flow and a blowing head with a set of fixed tuyeres opening into a front dome of the blowing head and dividing the supersonic gas flow into individual free jets. A cyclic modulator modulates a flow rate through the set of fixed tuyeres so that the flow rate in a first subset of tuyeres does not vary synchronously with the flow rate in a second subset of tuyeres, i.e., the flow rates in both subsets of tuyeres increase or decrease at the same time and they do not reach their minimum value or their maximum value at the same moment.