Complex sentence: To accommodate this, AC track circuits use alternating current signals instead of direct current (DC) but typically, the AC frequency is in the range of audio frequencies, from 91 Hz up to 10 kHz.
Split into simpler sentences: To accommodate this, AC track circuits use alternating current signals instead of direct current (DC). Typically, the AC frequency is in the range of audio frequencies, from 91 Hz up to 10 kHz.