Reed instruments have been categorized into two families since Helmholtz: the ‘‘striking inward’’ and the ‘‘striking outward’’ reeds. In an attempt to clarify the question to which family the lips of the brass player belong, a Helmholtz resonator with active feedback was used as a single‐mode brass instrument and the playing frequencies generated by three trumpet players were measured. By adjusting the gain and the phase in the feedback loop, the resonant frequency and the quality factor of the resonator can be varied. The acoustic impedance at the mouthpiece is measured by a novel method without removing the player’s lips. The results show that with extreme efforts the players can generate playing frequencies both lower and higher than the corresponding air column resonance, but that the playing frequency under normal playing conditions (the ‘‘most comfortable note’’) is almost always higher than the corresponding air column resonance. This supports the view that human lips function as ‘‘striking outward’’ reeds.