music via spdif?

[johnsonx42]

I just switched from an old analog surround-sound receiver to a newer dolby digital receiver, along with a set of much smaller speakers (using center and L/R, no surrounds right now), along with a sub-woofer.

I initially hooked it up the same as my old system, with the analog cable from the htpc to the receiver. TV and music sounded quite good as well - TV was being processed as 3.1 surround, while music was sent to the l/r speakers and sub-woofer (2.1).

My HTPC has a coax digital audio output, so I figured I ought to make use of it. I connected it up and configured both Windows and AC3Filter to use the SPDIF output, and TV audio now sounds pretty awesome - it's making explicit use of the low frequency effects channel and I'm hearing things I never heard before.

On the other hand, music now sounds very weak. It's being output as 2-channel stereo, and the receiver is being quite literal about it and sending the audio only to the l/r speakers and isn't using the sub at all. These tiny speakers just aren't up to the task without the sub.

So the question is, how do I get music sent over SPDIF in a 2.1 or 3.1 format? How do you guys with digital receivers handle this? Or is my receiver just too stupid?

(I'm using NPVR's built-in music player, if that makes any difference)

[johnsonx42]

ok, I seem to be part way to understanding here... I looked in NPVR.log and found it was using the Microsoft MP3 Decoder DMO filter for playing music... I figured this is probably outputting just 2 channel audio. AC3Filter's configuration says it's supposed to be the default for every audio format it supports, but I recall that Windows 7 can be a little difficult about this. So I fired up "Win7DSFilterTweaker 5.9" and checked "Disable MP3 Decoder DMO" and then played music again. The audio is still coming out as 2-channel only, but now AC3Filter is definitely handling the audio - it shows in the NPVR.log, and the AC3Filter icon appears in the system tray when I play music.

The weird thing is that AC3filter is telling me that it's outputting 3.1 audio via SPDIF, but that's not what I'm getting. Still poking at it...

[johnsonx42]

ok, I figured it out. Not sure I'm happy with the results, thought music sounded better when I just let the receiver process it on it's own as analog stereo.

However, for anyone reading along, the problem was that AC3Filter defaults to only allowing 48Khz audio. My MP3's are almost all 44.1Khz cd-rips, so AC3Filter was turning off it's SPDIF output and passing the audio to the windows shared-mode digital audio path, which is stereo-only. I found two solutions that worked, couldn't really tell any difference - set the output format to 48Khz so that AC3filter re-samples on the fly, or allow 44.1khz audio as well which my receiver can handle. I guess the latter is theoretically better, as re-sampling 44.1khz to 48khz when the receiver can handle 44.1khz seems silly.

Now that I have the basics sorted, if anyone has suggestions about better settings in AC3Filter or another decoder I would welcome your insight.

[thisheat]

FWIW, I have the same problem (well, more of a gripe than a problem, I guess). That is, settings which sound great for TV/movies sound pretty poor for audio. Digital audio output increases this effect IMO. I've never really hit upon a solution that works well for both.

I would try fiddling with the EQ in ac3Filter to try and find a happy medium. I don't know of a way to to switch EQ presets on the fly.

If your receiver remote can switch between EQ presets, the best solution might be to have one for music and one for video programmed into the receiver. Less than ideal, but hopefully better than the default EQ.

Hope this helps.

[whurlston]

LAV Audio works well for bitstreamed formats.

[johnsonx42]

I've figured out some more looking at the manual for the receiver. It seems I created part of the problem myself. When I was setting up the SPDIF output in Windows, there was a setting for the bitrate to be used for "shared mode", or sound produced by regular windows apps that know nothing specific about SPDIF. I set it to 16-bit stereo, 96khz, since that was the highest setting I knew the receiver supported. I didn't think it would genuinely sound better than 48khz, it just seemed reasonable to choose the highest setting. However, somewhere in the manual I discovered that the receiver turns off all it's signal processing when presented with a 96khz signal, and treats it as pure stereo. Apparently if I had just left the setting at 48khz, the receiver would have taken the digital stereo signal produced originally by the "Microsoft MP3 Decoder DMO" filter and processed it to much like it had the analog signal - sending it to the L/R and subwoofer, or even to all three front speakers depending on which mode I chose.

However, making that mistake led to learning and other discoveries; I know a lot more about how various settings in AC3Filter work, re-learned at AC3=Dolby Digital (I knew that, but didn't initially remember that I knew it), and learned how to control what decoder will be used for music.

[johnsonx42]

oh good grief, I almost wish I'd never been given this digital receiver and speaker set. Now I've got audio-sync issues which I've never had before. It's ok on recordings, but on Live TV the audio starts in-sync but within a few minutes drifts more than a second ahead of the video, and then starts dropping out periodically as well. LiveTV is now unwatchable. While watching football a bit ago, the announcers were so far ahead of the action they seemed to be psychic, announcing catches and fumbles before they happened.

I'm very tempted to just go back to my old analog Denon AVC-2800. If I leave digital audio out of the equation, then the Denon is FAR superior.

[whurlston]

but on Live TV the audio starts in-sync but within a few minutes drifts more than a second ahead of the video, and then starts dropping out periodically as well. LiveTV is now unwatchable.

Config.xml:

Code:

<Renderers>
    ...
    <ForcedLiveTVClock>[color=#FF0000][B]AC3 Audio Renderer[/B][/color]</ForcedLiveTVClock>
    ...
  </Renderers>

(Obviously don't put the "..."s in there.)

[johnsonx42]

ok, I'll give that a try. Further expirementing says this is yet another variation on the old choppy/stuttering audio problem. If I disable the MP3 decoder, then the audio-sync problem goes away which is exactly the same as the choppy/stuttering audio problem. I think this has to be an NPVR bug, but sub can't reproduce it.

[whurlston]

ok, I'll give that a try. Further expirementing says this is yet another variation on the old choppy/stuttering audio problem. If I disable the MP3 decoder, then the audio-sync problem goes away which is exactly the same as the choppy/stuttering audio problem. I think this has to be an NPVR bug, but sub can't reproduce it.

Do you mean the MPEG1 Audio decoder (not MP3)? NextPVR defaults the clock on the LiveTV DirectShow graph to the m2a renderer unless you change that setting in config.xml. If you are listening to an AC3 stream, you will get sync issues and if they are bad enough, it can cause stuttering.