In the commercial equipment, the audio bandwidth tends to be narrower than our amateur equipment and there are circuits installed to filter out the tones so they are truly subaudible.

• 在商业设备中，声音频宽比业余设备更窄些，并且，配备有专门的电路用于过滤音频，于是，这些音频信号真正的成为了“亚音”，不会被听到。