spdif / pcm / dolby digital output on realtek 7.1 / Gigabyte Ep45-DS3r

[bastian74]

I thought I'd mention some observations I have made with this motherboard / onboard realtek sound regarding digital outputs.

First, my TV does have HDMI 1.3 inputs, but my home theater receiver does not, and the TV only passes stereo sound out the built-in toslink for some reason. (Samsun 67" dlp) Apparently the toslink only passes dolby digital for OTA.

So I must use the sound card to output sound to the home theater receiver, and video card to the tv. Since the HDTV takes some time to process the video it can create audio synch issues, and you have to deal with that through software delay of sound. You can measure the delay by hooking a laptop up to your tv and launching an high speed stopwatch application, then taking a picture with a camera of the two together. The time difference of the tv to the laptop is your delay you want to apply to your sound.

I've realized there are two ways to output digital sound to an external receiver.

In the Gigabyte sound mixer there are settings for the analog inputs, digital inputs and speaker layouts. Ensure spdif output is set to enabled.

I was originally using speaker layout to 5.1 and digital output to "output digital audio source" then in the ac3filter/player settings I enabled spdif output for AC3 and DTS. With spdif output from the application the number of speakers you have set in the soundcard utility doesn't mater because the raw audio is passed to the home theater decoder.

When the player does not have spdif output checked, sound is output in pcm stereo over the spdif output.

This makes things confusing because digital sound goes out the spdif interface in ac3filter with spdif checked and unchecked. (it sends the raw ac3 stream when spdif is checked and the soundcard encodes pcm stereo when spdif is unchecked) All applications (including windows sounds) will be sent out pcm stereo.

In ac3filter with spdif checked, this passes the digital audio from the source file to the external audio decoder unmodified, but different players have different support for spdif outputs. The sound quality is as good as it gets but I couldn't get everything to work without having to mess around with settings frequently. Some of the applications didn't even have the spdif output option, or when enabled the receiver couldn't figure out the codec and I'd get "spdif unlock" on the receiver display.

Also, you cannot mix sounds when you are passing through ac3/dts to the receiver which means you cannot hear audio from a ac3 source and a stereo sound file at the same time. It's AC3 or PCM or DTS, one at a time. Regular OS sounds from windows (sent in pcm) may confuse the soundcard / home theater receiver when you are trying to play back a multichannel stream.

Then I realized that I can change the speaker layout in the sound card utility to "Dolby Digital 5.1" instead of "6CH Speaker" and the on-board sound card re-compresses the analog multi-channel sound from any souce back into DD 5.1 and sends it out the SPDIF jack reliably. For this to work you actually UNCHECK spdif output in ac3filter or what ever player you're using and set it to the number of analog channels (5.1)

Bascially, what the Dolby Digital 5.1 setting does in the realtek settings is intercept the sound going to the analog 7.1 speaker outputs in the back of the computer and encode them into ac3 and put them out the digitial outputs instead. This turns off the analog outputs as the "6CH speaker" and "Dolby Digital 5.1" settings are mutually exclusive.

This has the negative impact that dolby/dts sound is decoded on the pc, processed and then re-encoded before being sent to the home theater receiver. However it has the positive effect that every application works with multi-channel sound and you don't have to rely on them providing a spdlif output and it working with your source material and receiver. It also has the "benefit" that software audio processing tools work.

For example, in ac3filter, if you enable spdif output, all of the mixers and levels go grey or zero out. If you dissable spdif output and use 5.1 analog output you can adjust the equalizer and the mixing of the channels. For example, I copy my LFE track to the two front speakers at 2x their regular power because I have very large front speakers and no sub.

[timg11]

I have the same problem with my GA-P35-DSL system. The Realtek control panel does not have the "Dolby Digital 5.1" option. It only lists Headphone, and 2, 4, and 8 speaker modes.

I can get stereo to my receiver over SPDIF, but not DD 5.1.

What version of the Realtek control panel do you have? I have the latest drivers from their website (5.10.0.5565).