Choppy Audio Due to Possible Incorrect Filter Graph

[PVRDon]

To try and clarify:

I am already using the "<ForcedLiveTVClock>AC3 Audio Renderer</ForcedLiveTVClock>" in my config.xml. I updated it after reading other posts in this forum. However, I did not send this version of my file.

The audio stuttering problem appears to be caused by having both the MPEG1/2 decoder and renderer active at the same time as the AC3 decoder and renderer. And, it only happens to a few of the channels. For example, the HDHomeRun channel scan shows the following:

SCANNING: 195000000 (us-bcast:10)
LOCK: 8vsb (ss=100 snq=92 seq=100)
TSID: 0x0887
PROGRAM 1: 10.1 WHEC-TV 1920x1080i 16:9
PROGRAM 2: 10.2 MeTV 704x480i 4:3
PROGRAM 3: 10.3 WHEC-WX 704x480i 4:3

Channel 10.1 is HD and works perfectly
Channel 10.2 and 10.3 are SD and have the stuttering problem.
All three channels are AC3 - I can disable the MPEG1/2 decoder and the audio works fine on all three.

So, if there was a "Force AC3 on LiveTV" option, that could be used to tell nPVR to create a filter graph with only the AC3 decoder and renderer.

I hope this helps to explain the problem.

Donald

[johnsonx42]

Do any of you ATSC guys have a frequency that happens to have both an HD channel with AC3 and a SD channel with MPEG1? I don't have anything like this in New Zealand, which might contribute to me not seeing the problem. If you can supply a sample file, I'll try it here with my ATSC signal generator to try again to reproduce it.

As far as I can see now, all digital channels here, whether cable or ota, now use AC3 audio exclusively. It's the analog channels that have mpeg1 audio. That's why I previously asked (in a pre-release thread) if you could differentiate between digital and analog channels when first starting live TV, and force the correct reference clock. It would break on channel-changes of course, but that's no worse than now.

[PVRDon]

Problem apparently solved: I uninstalled AC3Filter 1.62b.

Even though it was not selected as an MPEG1/2 decoder, it was apparently causing some sort of interference. This filter set has been recommended in this forum, so I installed it some time last week.

This is the first time an installed codec has caused a problem for me. I have several codecs lying around that seem to be dormant when not used.

I tried to do a lot of debugging on my own before posting on this forum. I guess sometimes it is just a very tedious process of elimination.

My thanks to all who tried to help.

Donald

[johnsonx42]

Wait, so what audio decoders do you have set now?

also, are you really sure the problem is fixed? I've thought many times some change I made had fixed this issue, only to discover the problem was still there.

[PVRDon]

Here is my current Decoders settings screen.

It has the same decoders as shown on the filter graph of my original post.

I listened to various channels for over an hour - all those that had a problem before. Now they are all clean.

I also have some audio decoders from a WinDVD installation. They work also, but the AC3 decoder is louder.

Thanks for your interest.

Donald

[sub]

It'll be interesting to see if other users with this problem see the problem go away if they uninstall AC3Filter. It'd be odd but you never know.

[PVRDon]

I found some new channels after switching to ATSC from cable. One channel was choppy and I thought it was due to signal strength, which was bouncing around 58%. I am listening to it now and it sounds like a CD.

I decided not to try AC3Filter because of the configuration screens. I am completely tapped out on configuration settings...

Donald

[whurlston]

Do any of you ATSC guys have a frequency that happens to have both an HD channel with AC3 and a SD channel with MPEG1? I don't have anything like this in New Zealand, which might contribute to me not seeing the problem. If you can supply a sample file, I'll try it here with my ATSC signal generator to try again to reproduce it.

I will check all my channels tomorrow but I'm pretty sure that all mine (both HD and SD) use AC3 audio. There might be a secondary audio stream with MPEG 1 though.

[johnsonx42]

I've been wondering if there are any audio filters that do absolutely nothing except pass the audio to a digital ouput? Decoders like AC3Filter can be configured in pass-through mode, but I'd like to try one that's truly just an empty pipe.

[whurlston]

do absolutely nothing except pass the audio to a digital ouput

It wouldn't work. The audio bitstream has to be "packed" before it can be output via HDMI/SPDIF (and yes I did try writing a filter that did just that.. passing it through that is). Otherwise, we would have had bitstreamed HD audio on day one.