Many mobile operators have upgraded their networks to support the HD Voice standard. This provides the same audio benefits as HD calls on an IP network. HD audio produces much more natural-sounding speech than the sound you get with conventional phone calls. All the nuances come through, making conversation more fluid. HD calls, also known as wideband audio, use at least double the frequency range compared with conventional telephony, from 50 Hz to 7 kHz or higher instead of just 300 Hz to 3.4 kHz.