AC3 and Me.

[123tim]

I'd like to hear the opinions of someone who considers themselves to be an "audiophile" on the subject of AC3 optical outputs and surround sound. Or maybe you aren't an audiophile, but have an opionion anyway?

When I purchased my Fortec Star Classic NA I knew that I would eventually end up buying a decoder/amplifier to process AC3 signals. Long story short, I ended up buying it a lot sooner than I thought, and (of course) buying a lot more than I originally thought that I would. I now have a huge Kenwood 150 watt (per channel) home theater system setting next to my TV (that I picked out of the trash) and beside my FTA receiver which cost a lot less than the surround sound system.
I'm sort of a minimalist, and even though I've wanted an amplifier for years, I'm sort of horrified at what I see sitting beside my TV. Even so, I got a really good deal on it, and for years I've wanted something that I could pipe music (stereo) through the house. Now have it.
My questions (statements) are these:

Why would anyone go to the trouble of designing an optical transducer circuit to run a digital signal over an expensive fiber optic cable when a RCA output connector works (apparently) just as well, or even better?

Does "surround sound" actually sound good if you aren't centered exactly between the speakers? I move around a lot...I don't like the idea of being stuck in one spot. On a similar note I always thought that stereo sound was supposed to simulate sound in different positions, so, why is surround sound so much better? (I suspect that it's more the sound (feel) of the sub woofer more than of the other six speakers.) I personally am unimpressed by surround sound.

I wonder why the AC3 couldn't have been converted to plain stereo internally in the receiver. (I know that it's possible....I wonder why it wasn't?)

Well, these are just things that I wonder about...Please forgive my opinions - I'd like to hear some of yours.

Thanks.

 

[W_Tracy_Parnell]

Here is my opinion and an expert may feel free to correct me if I am wrong.

As far as FTA is concerned, there is only one channel I am aware of that is broadcasting in Dolby 5.1 and that is PBS HD. Everything else to my knowledge is Dolby Stereo only. You can prove this to yourself because sometime one of the PBS channels will have the same program playing on the HD station. Listen carefully and you will hear the surrounds come into play when you switch between the two. Now, this may not be true of every program but there was a show on recently about the French-Indian wars and you could hear the difference very clearly-even my wife could.

As far as a "sweet spot" for 5.1-yes there is an optimum place to sit and in fact you are susposed to setup your system to take advantage of that spot (presumably your living room sofa or favorite easy chair). As far as sound quality, it is just that with the rear speakers it creates a bigger soundfield and as you mention the subwoofer enhances bass and sound effects etc.

 

[Larry1]

Why would anyone go to the trouble of designing an optical transducer circuit to run a digital signal over an expensive fiber optic cable when a RCA output connector works (apparently) just as well, or even better?

There are lots af arguments over which one is better, but for me, digital is digital. It does not make a difference if it is transfered by way of an electric field over a copper wire or a light over a plastic (or glass) cable. The fiber optic cable does have an advantage of that the two conponents are electrically separated and you have no ground loops to contend with. This shows up as a hum in the speakers or a rolling bar in your picture. A copper is also influenced by elecrical noise, and around a home theatre setup you have a lot of electrical equipment creating a lot of electrical noise. A beam of light is less dependant on a magnetic field. With light there are no elecrical shorts, corroded connections, etc. Now why a piece of plastic is more expensive than a piece of copper wire? Marketing?

 

[Tron]

Interestingly enough, you can run coax digital over longer distances than you can with TOSLINK optical. I guess that's because the optical carrier used in typical TOSLINK cables isn't made of high quality material. AES (professional SPDIF digital) also uses coax in its unbalanced version, employing BNC connectors though instead of RCA. These cables can be run well over 100 meters.

As WT pointed out, most AC-3 channels are only two-channel digital. They use AC-3 (Dolby Digital) only to compress the audio portion of their signal. I have always assumed they use AC-3 to conserve on bandwidth, as conventional, uncompressed PCM adds more to the bitrate of the stream.

 

[123tim]

I have always assumed they use AC-3 to conserve on bandwidth, as conventional, uncompressed PCM adds more to the bitrate of the stream.

Tracy Larry and Tron,

Thanks for the input.
One of the frustrating things (to me) about the Tosiink fiber optic connection is that it really cuts down on your choices when you're looking to buy. It seems that only about 25 percent of the decoders manufactured have this connection.

What Larry said about the induced noise really makes a lot of sense, especially with the Sub Woofer (which I currently have turned off.)

I didn't know that the most of the AC3 was just straight stereo (not really surprising, because I know next to nothing about AC3, or surround sound.)

I did know that I was somewhat disappointed in the sound. Maybe when I find a true surround sound signal I'll be impressed.

Not AC3 related, but I was also sort of disappointed to find that the Kenwood shuts down to two speakers when in Stereo Output mode. I thought that it might output the same signals to the front and back, left and right, but it doesn't. I had planned to use this to pipe music through the house. Shouldn't be too hard to work around though.

In my opinion (which doesn't count for much) I think that a RCA connection would have been a better choice for an FTA receiver (rather than the fiber optic that the Fortec came with.).

I still think that the Fortec NA is great even so.

Thanks for your input! I feel a little better, and know a little more now.