The work presented is an experimental study on the influence of the blowing pressure profile on the attack transient of the clarinet. A clarinet mouthpiece connected to a straight cylindrical pipe was played by an artificial mouth in which the blowing pressure can be accurately controlled through time. Piece-wise linear time profiles are used for the blowing pressure. The observed oscillation threshold as well as the envelope of the mouthpiece pressure are analyzed for different configurations and compared to predictions from the Raman model. Differences between predictions and observations are interpreted in terms of bifurcation delay. Firstly, the pressure is increased constantly at several different rates until the oscillations are well established in the resonator. The oscillations are seen to start at a value of the blowing pressure which is higher than expected from a stationary analysis. This value is as high as the slope of the pressure increase is higher. In a second time, a fast linear increase of the blowing is suddenly stopped at a target pressure value. In this case, the oscillations are seen to start close to the stop in pressure increase, or before this instant. The transient time of the resonator pressure is constant.