In this article, the first of a series covering HD Voice, we discuss the issue of audio bandwidth for VoIP systems, and in particular, how much audio bandwidth do you actually need for voice?
Voice communications systems in use today are based on traditional telephony standards that haven't changed much since the 1950s. These standards were set at that time and limit the information bandwidth for voice communications to 300-3400Hz (200-3200Hz in the US and Japan). However, if one analyses normal conversational speech, it typically covers the frequency range 0-8000Hz. In fact, only 20 percent of the frequencies utilized by the human voice are transmitted in the 300Hz to 3.4kHz range. Furthermore, the human ear is capable of hearing frequencies up to 18 or 20kHz. Back when these standards were set, it was felt that a voice channel limited to 3.4kHz would be good enough and ever since that time we have all accepted that telephone conversations would have a slightly muffled tone.
Voice communications systems in use today are based on traditional telephony standards that haven't changed much since the 1950s. These standards were set at that time and limit the information bandwidth for voice communications to 300-3400Hz (200-3200Hz in the US and Japan). However, if one analyses normal conversational speech, it typically covers the frequency range 0-8000Hz. In fact, only 20 percent of the frequencies utilized by the human voice are transmitted in the 300Hz to 3.4kHz range. Furthermore, the human ear is capable of hearing frequencies up to 18 or 20kHz. Back when these standards were set, it was felt that a voice channel limited to 3.4kHz would be good enough and ever since that time we have all accepted that telephone conversations would have a slightly muffled tone.
