When using a stepped sine stimulus, each frequency is played for a certain number of cycles. before it steps to the next frequency point. When the stimulus changes frequencies, the driver excursion takes a moment to respond to the change in frequency. This is known as settling time which, produces the phenomena known as ‘ringing’. Due to the greater excursion at low frequencies, settling time is longer when changing from a low frequency (greater excursion) to a higher frequency (smaller excursion) than vice-versa. Long settling times can create measurement inaccuracies. While this can be minimized by slowing down the stimulus, a better solution is to sweep from high to low, as this minimizes settling time and enables accuracy to be maintained at faster test speeds.
The Stweep test signal itself also minimizes settling time. Originally launched with SoundCheck version 1 back in 1995, this was the first stepped sine wave test signal to use an integer number of cycles at each frequency step. With frequencies changing at zero phase and amplitude, transition between frequencies is smooth. This also reduces transducer settling time, resulting in faster and more accurate measurements. This is still one of the most widely used acoustic test signals in use today!