The cut-off spatial frequency is got higher at the cost of the loss of mid-spatial frequency, and the information got by the system are different in all directions.

The results show that there exist attenuation in all propagation modes along viscoelastic cylindrical tube, and higher-order propagation modes haven't cut-off frequency.

And in the talk program, only cut-off and sound stretches appear. The frequency of the formal is much higher than that of the latter.