# HDMI Coaxial Optical 5.1 and 7.1



## GeoMoon5 (Sep 5, 2008)

Hello!

Why exactly does a coaxial audio connection and an optical audio connection only support 5.1 sound, but a HDMI audio connection supports 7.1 sound?

In theory, wouldn't an optical cable be able to support way more bandwidth then an electrical cable such as coax or HDMI?

Is the reason not because of the cable, but because of the agreed upon standard for optical signal transfer? (The cable could handle much more data, but the current optical standard limits optical data transfer to 5.1). Maybe the current limitation on optical audio is because of the LED used in home theater optical acoustics? In other words, the reasonably priced LED can't flash on and off fast enough to support the robust codecs used in digital 7.1 sound? Maybe the current audio chips that process the sound for the optical connections can't run at a high enough frequency?

If the limitation is merely because of the audio chip or the LED, couldn't the optical connections suddenly become a way better choice in the near future if the standards/chips change?

Any help is much appreciated,
Thanks!


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## ebackhus (Apr 21, 2005)

I'm wondering this as well! I bought a 7.1 system back before HDMI was around and yet it only allows inputs over lines that apparently carry only 5.1. I can't really tell the difference especially because it's currently only using 3.1 due to speaker placement issues in my apartment.


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