The human voice can create sound energy in the range of 80 Hz to 14 KHz. In contrast, the PSTN conveys a much more limited pass-band, typically 300 Hz – 3.4 KHz. That means that the PSTN fails to convey more than 70% of the potential energy in a voice.
To find a visual parallel to this consider displaying a picture of some text. If the original speech is 100% of the information, then the following image is the equivalent of HDVoice.
The text is from President John F. Kennedy’s address to congress seeking funding for NASA’s lunar exploration program. That image started out at it’s original dimension, then I reduced it to 80% of its original dimensions.
By extension then, the PSTN version of the same information would be reduced to only 30% of its original pixel count, which looks like the following:
The contrast in detail makes for a striking change in slides when shown in a Powerpoint presentation.
The point I’m trying to make is that HDVoice is very simply easier on the brain. The presence of greater detail in the audio stream reduces cognitive workload, making it easier to understand what’s being said. This is why conference calls in HDVoice (ZipDX!) don’t leave us feeling as drained as similar calls hosted on traditional, narrowband conference services.
This was part of the presentation that I gave at the CloudComm Summit 4 during ITExpo this week. Given a little time I think that I’ll record some narration to go along with the slides and offer the whole presentation hereabouts.