5.1 audio problem

Sebaz wrote on 1/29/2010, 2:15 PM
No matter what audio output device I choose in the preferences, I can't get the timeline to play out in real 5.1. My receiver accepts both Dolby Digital and DTS, and the motherboard in the computer has coaxial and toslink digital outputs. The receiver is connected to the coaxial one. I know Dolby Digital works fine from the computer because when it's playing a TV show encoded in DD from Media Center the receiver shows me it is receiving a DD signal, and also when it plays a DVD.

However, no matter which of the three options I select in Vegas (MS Sound Mapper, Direct Sound Surround Mapper or Windows Classic Wave Driver selecting S/PDIF for all three items) I can't have Vegas send Dolby Digital to the receiver. Is this a limitation of Vegas, or a limitation of my motherboard? As far as I can tell I mapped everything correctly because when I exported the audio to an AC3 5.1 file (as well as the video track) and then put both in a SD DVD in DVDA 5, the result plays as it should when I put it in my blu-ray player which is connected to the same receiver with the Toslink cable.

Now, I suppose I could run cables from the 6 analog outputs of the motherboard to the same inputs in the receiver, but taht would mean buying 30 feet of 6 mono 3.5 mm to RCA cables (unless Monoprice has a combo already made for this), so I'd like to find a way to make what I already have work. Is there a way?

Comments

Rob Franks wrote on 1/29/2010, 2:31 PM
What I can tell you is that it is not a Vegas limitation. I can get 5.1 fine out through the computer sound card and out through toslink to the receiver. Vegas does its job with routing tracks and channels just fine. However all of that is useless if you haven't the proper hardware to properly support Vegas's output.

I am not however using the on-board sound card. I have both X-Fi and maudio cards (used with ASIO drivers) and all works fine with both cards.

If you're going to get into 5.1 sound then I would suggest nothing less than a ASIO supported sound card of one kind or another.
musicvid10 wrote on 1/29/2010, 2:37 PM
The Vegas timeline does not encode or output 5.1 surround. It will, however, output six discrete audio channels from your surround project. This is an important distinction to understand.

In order to Preview the surround mix from the timeline, you need a sound interface with six discrete I/O channels (not a 5.1 card), and the signals from the audio tracks need to be routed to the appropriate input channels to work properly.

There were a couple of older threads on this, where I got my education about it. You should be able to locate them with a search.
newhope wrote on 1/30/2010, 3:42 AM
I second Musicvid's explanation.

Vegas can render Dolby Digital 5.1 but no audio post program plays it that way off the timeline during the mix, it's all fed as discreet channels leaving the encode process until the mix is completed.

You need to mix with discreet 6 channel (5.1 unencoded) outputs first. You can then render using the Dolby Digital encoder once you have completed mixing but monitoring during the mix requires feeding the six discreet channels into discreet inputs on your amp.

I use the analogue 5.1 inputs on my Yamaha amp to achieve this. I can then use the optical input to feed the encoded signal after I have rendered it, usually off a mastered DVD.

New Hope Media
musicvid10 wrote on 1/30/2010, 7:00 AM
I think newhope actually explained it a little better than I did.

BTW, 6-channel out from the timeline is going to sound different than the 5.1 encode anyway, so after I get my basic levels and balance set, I burn DVD-RW tests and play them on the home entertainment system.

One of the great advantages of DVD Architect is that I can render out a new audio track in a matter of minutes rather than re-rendering the whole darn thing.
newhope wrote on 1/30/2010, 1:02 PM
In professional studios mixing for 5.1 they normally run the discreet outputs into a Dolby hardware encoder that is set up to encode the signal into Dolby Digital and then from that route it through a hardware Dolby Digital decoder so that what the mixer is listening to has gone through the encode/decode process and any anomalies can be heard and rectified before the mix is completed.

Even with this process they still output discreet tracks of the final mix and do an encode of those, using the encoding hardware, in a similar manner to rendering your AC3 track in Vegas after the mix is complete.

New Hope Media
LoTN wrote on 2/1/2010, 1:31 AM
Now, I suppose I could run cables from the 6 analog outputs of the motherboard to the same inputs in the receiver, but taht would mean buying 30 feet of 6 mono 3.5 mm to RCA cables (unless Monoprice has a combo already made for this), so I'd like to find a way to make what I already have work. Is there a way?

This is the way I did things for a while using my own "hand made" snake:


This is a working and cheap solution but I must warn you that with 30 feets you can expect a very significant loss of signal quality unless you use symetric links. On my side I decided to replace the analog 8ch snake (10 meters) with one ADAT over fibre link.
TheHappyFriar wrote on 2/1/2010, 4:51 AM
you can get 30' of shielded 1/8" stereo cable from radio shack pretty cheap, then hook up a shielded 1/8" stereo to left/right RCA cables.

It works, sounds decent. I did that for years (I never noticed a difference between Vegas's 5.1 & the DVD, IF you encode it as expected).
LoTN wrote on 2/1/2010, 7:44 AM
It works, sounds decent. I did that for years (I never noticed a difference between Vegas's 5.1 & the DVD, IF you encode it as expected).

Some sound cards have low impedance output stages that can even drive headphones. If you do not want to loose any signal quality, this limits the length of unbalanced cables.

So you never eared any loss in the high frequencies ? What is the impedance of your souncard output stages ? My M audio FW410 ouput impedance seems to be low enough to show that an unbalanced analog path is not the solution with a 30ft. low capacitance cable.
musicvid10 wrote on 2/1/2010, 9:42 AM
The most common commercial solution to long unbalanced audio runs is a multichannel DI box and an xlr snake. In your case you would have to have a DI at the receiver end too to switch back to unbalanced.
LoTN wrote on 2/1/2010, 9:52 AM
Fully agree. On my side I'll get rid of the snake. ADAT rocks.