When VoIP applications like softphones started to use wideband codecs in 2003, they gave a major boost to the VoIP market.  The improvement from narrowband codecs that use 3.4 or 4 kHz, to wideband codecs that use 7 or 8 kHz, was a giant step in terms of perceived voice quality, and totally changed people’s views on VoIP’s legitimacy.

Today there is a lot of talk about HD audio (usually referred as wideband) and super wideband codecs that use 14 or 16 kHz bandwidth. I have been listening to different audio and music samples with 3.4, 7, 8, 14, 16, 22 kHz to get a better understanding of the quality differences. As anyone who has tried Skype or Google Talk can attest, there is obviously a big difference when going from narrowband (3.4 kHz sampled with 8 kHz) to wideband speech (7 or 8 kHz sampled with 16 kHz). The bigger question is, can people hear the difference when using 7, 8, 14, 16, or 22 kHz in a normal voice conversation?

In my opinion, there is an audible difference when moving from a 7.0 kHz sample to a codec that supports 8 kHz, such as iSAC and iPCM-wb. However, there is a much less obvious difference between 8 kHz and 14 kHz, which I can only detect after listening to a speech sample several times. I experimented with different headsets and speakers, and found that studio grade equipment can accentuate the quality of the super wideband samples, but not to an extent that the average user would be able to regularly appreciate.  Furthermore, super wideband codecs are more susceptible to background noise, to the point that my experience was actually much worse using 14kHz than 8kHz when I added even low levels of ambient noise. Once I went beyond 14 kHz, I was unable to hear any difference in quality at any range for speech or even music.

The basic conclusion of my simple tests is that quality differences between wideband and super wideband are not obvious above 8 kHz, but can be detected by using the right equipment.

There is obviously still more work to be done to provide the most robust speech quality for IP communications. Super wideband may end up pushing the market even further, but the jury is still out. Regardless of what transpires, GIPS will continue to support a wide range of codecs to provide the best user experience possible.

Tags: codecs, Google Talk, Skype, wideband

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