HDMI vs. Optical Audio: which one to use?

I can’t seem to find straight answers on the net, so I come to you.

What is the difference between HDMI and Optical Audio in terms of audio quality?

Does HDMI carry surround sound audio to all channels in a 5.1 surround sound system?

If input and output devices support both formats, which one to use?

Scenario 1:
Input device: Apple TV (HDMI out, Optical out)
Audio output device: 5.1 surround sound home theater system (HDMI in, Optical in)
Video output device: Projector (HDMI in)

Scenario 2:
Input device: Cable DVR (HDMI out, Optical out)
Audio output device: 5.1 surround sound home theater system (HDMI in, Optical in)
Video output device: Projector (HDMI in)

Which one to use in the above scenarios?

HDMI allows for lossless audio, optical audio does not. If you have a source which is lossless (bluray, for instance) and a receiver that knows what to do with it (unless the source does the processing), then always use HDMI (unless your source also outputs in multichannel, which is incredibly rare these days - at which point either is fine). If you have the option, always go with HDMI over optical.

The Blu-ray player is built into the surround sound home theater system, so audio doesn’t need any cables. Blu-ray video would go to the projector over HDMI.

So, in the above non-Blu-ray scenarios, is HDMI better, equivalent to, or worse than Optical Audio? Will HDMI take full advantage of a 5.1 channel surround sound audio system? Conversely, will using Optical Audio sound different/better/worse than using HDMI in the above scenarios?

Toslink (digital optical audio) doesn’t support Dolby Digital Plus, TrueHD or DTSHD… So don’t use it if you want to pipe those to an amp.

I get that they each support different formats, but what I don’t get is the difference in audio quality between the two cable types. Also, my understanding is that only Blu-ray outputs in Dolby Digital Plus, TrueHD and DTS-HD, so it doesn’t apply to the two scenarios above.

Well, you could always be sending those codecs from a computer as well. In any event, HDMI does everything optical audio does, and more. Given the choice, always go with HDMI - there isn’t a situation where optical would be better (unless the situation is “I’m at Best Buy and have less than $35 to spend on an audio cable”).

You’re a mug if you spend $35 on a digital audio cable.

There won’t be any difference as the signals are digital. If they piping the same audio format, they will be identical. The difference is only about the supported audio formats.

Good point.

Great, thanks. This is the clarity I wasn’t getting elsewhere on the net. So HDMI will provide surround sound to all channels of a 5.1 speaker system, the same as would an Optical cable, for an input from a Cable DVR box, correct?

I’m buying all cables/switches/splitters from monoprice.com. What complicates matters for me though is that I’m running distances of up to 40ft, so I might go with their uni-directional HDMI cables, unless you guys have better recommendations. All the other 40ft bi-directional HDMI cables only carry up to 1080i.

HDMI will support 5.1 and more. (But not much more. 7.1 is about the limit.)

You will get 5.1 sound through HDMI, and you can use any of the major sound formats currently in use.

Don’t spend that much on a cable, seriously, you can get a 40’ HDMI cable for around $25 on Amazon.com, and as the signal is digital it makes no difference what the cable is made of. For massively long runs, you probably want a little shielding and to avoid running it near power cables, but other than that you don’t need any “special cable”.

Cables are a scam, digital cables are a huge scam.

“Audiophiles” are some of the most gullible people on earth, anytime spent on their forums will reveal how easy it is to relieve them of their money.

As an indication on cheap HDMI cables - I have a 10 metre (32 feet) cable that I paid $25 for from the local cheap computer bits place. Works perfectly with my gear at 1080p.

The different “grades” of HDMI are a minimum performance guarantee. They put the split for the normal and high spec at the difference between 1080i and 1080p - but this is simply to say that that absolutely guarantee that 1080i will work, not that 1080p won’t. HDMI uses LVDS (low voltage differential signalling) and the cables are functionally identical - the only difference being the allowed loss of signal down the cable. It would not surprise me to discover identical cable being sold at difference price points - simply on the basis that a person with X amount of money to spend requires separating from their money, and thus a product is needed at that price.

You can get into trouble with loss in the cables - but the more modern transmitter and receiver ships in use seem pretty robust. You will see failures to sync up, or negotiate the link, or possibly bizarre intermittent failures. But, as above, do not be fooled into paying a premium for cable - once the link works and is stable - there is no gain to be had.

The bandwidth available in an HDMI cable allows for pretty insane data transfer rates, and the audio transfer is for all intents unlimited. It supports more channels at higher sample rates and higher bit depth than anything that is conceivably useful.

That’s what I was trying to suggest.

Yeah, my post reads like a dig at you…wasn’t intentional.