Control SPDIF Volume with AC3Filter

AC3Filter Logo This is the second part of a guide on using AC3Filter in Media Center to control SPDIF volume. A common problem among Media Center users with an external digital receiver using SPDIF for output. AC3Filter can solve this problem by controlling the gain on the SPDIF stream before sending it through to the receiver. Now that we have AC3Filter working in Media Center by following this guide, lets get AC3Filter settings ready to control the volume level.

Access AC3Filter’s configuration from the start menu. The first setting to change will be the number of speakers in your setup. Using the drop down box select the correct speaker setup for your system. Then enable SPDIF output to enable AC3Filter to output a digital stream via SPDIF.

Main AC3Filter Settings

Next go to the “Mixer” tab and in the options box make sure that Auto Matrix is selected. Expand Stereo will enable stereo streams to be output as full surround. Normalize Matrix and Voice Control will balance volume output among all the channels and during large volume changes in the stream. You can also control the Bass Output Cutoff from this panel.

AC3Filter Mixer Settings

Finally, we have to allow the AC3Filter to output a modified SPDIF stream. To do this go to the SPDIF tab and uncheck all SPDIF pass-through options. Pass-through tells AC3Filter to send an unaltered stream directly to the receiver, turning these off allows AC3Filter to alter the gain which will simulate volume changing. If this doesn't work you can try to send a PCM signal through your soundcard or disabling the AC3 Encoder, though in many situations this can break DD and DTS encoding depending on your hardware. Differences in sound card hardware and recievers will alter the viability of this hack.

AC3Filter SPDIF Settings

That should be all there is to enabling your Media Center to control the volume of SPDIF output using AC3Filter! If you experience any problems make sure that AC3Filter is the preferred codec using this GraphStudio guide. More options on enabling AC3Filter to be the preferred codec can be found under the System tab in the AC3Filter configuration.

Troubles, successes, or experiences with AC3Filter you want to share? Leave note in the comments below!


Ian said...

But you only describe part of the problem. You don't talk about how do you actually change the volume, once you have this configuration? The only way I have found is to go into AC3filter control panel and adjust the gain slider whilst file is playing back. This is not much use - clearl you want to be able to press "volume up/down" in either your playback app or the system volume you have any thoughts?

MHealy said...

Once you've disabled SPDIF pass through the ac3filter should be decoding the SPDIF stream then retransmitting the digital stream with processing such as gain done automatically.

After following these steps I was able to get volume control through my MC remote, though there seem to still be some problems with Windows 7 sound processing in the beta. A lack of Windows 7 specific drivers at this point can also complicate matters.

MHealy said...

You can find quite a bit more information on using AC3Filter with SPDIF at as well.

Anonymous said...

So, does it work w/b7022? Seems like a lot of work if the remote won't work...I'll probably try it anyways...

Ian said...

thius is the only page I have ever found discussing the use of this feature of ac3filter. actually I am using plain vista, and testing with mediaportal as well, but it shouldn't make a difference to the way ac3filter is behaving? I have followed all these guides, and I am 100% sure I am getting AC3 decode->process->recode to AC3 behaviour of ac3filter. I move the ac3filter gain slider - the spdif output DD5.1 signal level changes. But any other slider (in the system sound volume mixer) has no effect.

which volume sliders (open system mixer) move for you when you are getting a change in output volume? Is your receiver definately getting a DD5.1 signal?

MHealy said...

Actually the first program I got this to work in was Media Portal on a Vista machine. I remember finding a forum post on it back when I was running Media Portal. I'll see if I can find it again. I went back to test this again today on my 7MC, I normally use FFDShow audio, and low and behold I can't get it to work again either.

When I was using Media Portal it would output a DTS stream with a modified gain just fine for me though.

MHealy said...

I was able to get this working again using an older version of my soundcard drivers for some reason. Disabling passthrough and setting output to PCM allowed the soundcard to output a DTS Interactive stream. I'm not sure if it was something the soundcard was doing to the stream or how well it would work on other systems though. I don't recall having to set the audio to PCM mode in my Media Portal setup.

Ian said...

those last two comments really helped, figured it out based on that. the mediaportal solution is
- use AC3filter as codec in MP
- configure AC3 filter to decode AC3/DD sound to PCM 5.1 (3/2.1 as they call it)
- configure sound card to encode PCM5.1 to DTS 5.1 (DTS interactive)

windows / application volume control now works for DD 5.1 audio tracks, they reach the receiver as DTS 5.1

MHealy said...

Glad you got it working. It takes a bit of mucking about to find the right combination of settings between the ac3filter and the sound card. If you need to control spdif volume through windows for whatever reason though it's worth the effort.

Michael said...

I have some problems with this. If I choose not to Use AC3 encoder I'm able to control the volume, but the signal is not reached as DTS 5.1.

I have a SB X-FI, and using Vista. I have set up VMC to use AC3Filter for AudioDecoder.

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