About HD Audio

Enabling Better Voice Quality

HD Audio Did you know the basic speech technology in traditional phone networks has not changed in 75 years? But with new digital technology sound quality has been greatly enhanced, by more intelligently utilizing the abundant bandwidth available through today’s broadband connections.

Simple Conferencing is at the epicenter of this evolution, delivering HD Audio quality by incorporating the ITU Standard wideband speech codec called G.722. Combined with Simple Conferencing’s sound enhancement technology you can experience the highest quality in audio conferencing. Delivering a naturally-sounding conversation via audio conferencing requires sophisticated technology, normalizing sound levels, filtering background noises, and balancing audio streams. With HD Audio, the intelligibility of speech is greatly enhanced, and individual voices are easier to differentiate and understand, more closely simulating the experience of being in the same room around a conference table.

What are Codecs and How Do They Affect Sound Quality?
Sound quality is determined by the amount of data that is digitally sampled, transmitted and repackaged to reproduce the speaker's voice. Historically, telephone networks have used technology (called codecs) to minimize the amount of bandwidth required for transmission -- so they could carry more calls using the available capacity. Given the relative scarcity of wireless spectrum, mobile phone companies use more aggressive compression technology, which results in poorer sound quality. (To provide better quality would require either more spectrum, which may not be available, or smaller cell sites requiring many more towers.) That's why cell phones sound worse than landline phones, and why phone calls don't replicate your actual speaking voice.

A look at the numbers highlights the issue. There are two key factors:

Sample Rate. This reflects how many times per second the sound is sampled. Audio CDs sample the sound 44,100 times per second (44.1kHz), reproducing a frequency range of 20 kHz, which is the limit of audible sounds to most humans.
Bit Rate. This is the amount of bandwidth required. Sophisticated algorithms are used to minimize bandwidth, but the more aggressive techniques require more computations, leading to transmission delays (called latency). The effect of these techniques is to introduce delays between the time that the speaker talks and is heard on the other end. Fewer bits also means fewer "sound particles", which means greater deviation from the original sound.

During normal conversations, humans produce sounds from 80 Hz to about 8,000 Hz, with most normal speech occurring between 300 Hz and 3,000 Hz. (Singing or screaming can be outside this range, as you've no doubt noticed on phone calls.) Based on this, the traditional telephone networks were designed to transmit frequencies up to 3,400 Hz. The primary goal was to deliver sufficient quality to be understood, not to replicate speech quality.

There are three major codecs used by today's telephone networks:

G.711, providing the best legacy telephone sound quality, but consuming the most bandwidth.
G.729, used often for long distance transmission on landline networks, especially for overseas calls.
GSM-HR ("HR" stands for "half- rate"), used by cellular companies.

The table below compares these codecs with the HD Audio codec, G.722:

The bottom line is that G.722 provides a far superior audio sound with no noticeable latency, delivering a more natural conversation, with better clarity to discriminate between letters "S" and "F" or "P" and "T". This is especially true among female speakers, whose voices generate higher audio frequencies.

Using Simple Conferencing in HD Audio
To experience Simple Conferencing conference calls in HD Audio, you need two things:

A Polycom HD Voice IP phone
A broadband connection, since the G.722 codec is not enabled on legacy telephone networks.

Note: Any phone on any network or legacy system will work fine with Simple Conferencing. Those conference attendees just won’t experience the same HD Audio quality as the HD-enabled callers.

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