I have my STB hooked up via hdmi to tv..Last nite I wanted to listen to "The Unit" in surround sound. I turned on receiver and the sound was out of sync with the tv sound, sort of like an echo.. STB connected to AVR via coaxial cable. I turned down tv sound to enjoy the Sur. sound ..thanks in advance..

I turned down tv sound to enjoy the Sur. sound .

And that's exactly what you should do! :D

Ratman: so what causes the echo effect? shouldn't the tv sound be in sync with the STB sound coming out of the AVR? thanks for the quick response..

Ratman: so what causes the echo effect? shouldn't the tv sound be in sync with the STB sound coming out of the AVR? thanks for the quick response..
Well, there are a few reasons:
1.) The avr often does have a very slight delay in audio due to processingg. Though this should be so minimal to not be noticed.
2.) Differences in audio delay due to differences in distance. You'll hear an echo effect if one speaker is in front of you and one is behind you and no delay is taken on the one behind you to makeup for this difference.

If you heard an echo it is because your tv is not going through the same processing as the avr speakers, so no attempt was made to makeup for the differences in distance by delay.

However, it is nothing to worry about, if you're watching tv with the surround sound on, simply mute or turn down your tv.

Ratman: so what causes the echo effect? shouldn't the tv sound be in sync with the STB sound coming out of the AVR? thanks for the quick response..

As stated earlier... the AVR (via coax from STB) or TV (via HDMI from STB) could be delayed with digital audio processing. Digital to analog conversion may be "better/faster" in one device or the other. Just a few milliseconds difference will produce the "effect". Nature of the beast(s) I guess.

Yeah... they should be in sync, but as you now know, not a reality.

Personally though, for a "surround" experience, using the TV's speakers should not even be considered being used IMHO.