Very low volume on QAM channels

[feniks]

Hi people,

I have minor trouble with very low volume on digital QAM channels while having loud and clear audio on analog channels. Not sure if there anything can be done with that. I suspect my cable provider to be guilty one (Comcast of Meadowlands in New Jersey, USA)

Is anyone experiencing same issue with other providers, perhaps in other countries? or maybe it specific only to my provider?

thanks for replies.

[merc82]

I notice the opposite with QAM stations much louder than analog. This is through my TV tuner as I've be unsuccessful getting any channels on QAM with my HVR-1600.

What I also notice is the QAM stations on my cable company were AC3 encoded while analog channels were PCM. You therefore might be able to tweak your AC3 decoder (AC3filter or ffdshow perhaps?) to normalize one sound format to the other.

[mikeh49]

Good point on the AC3 encoding of QAM. Analog TV has only 2 channel stereo. Look at the properties of your audio decoder and confirm that the speaker arrangement in the decoder matches what you are using. Typically, for AC3, you will have various surround sound speaker configurations to select. I had to change from receiver to TV speakers on my Nvidia decoder to get correct stereo sound. AC3 Filter also works well for me and it's free.

[feniks]

merc82, thanks for input. Interesting insight.

I have this problem only with QAM on my digital tuner on HVR-1800 (analog tuner works great). I noticed that QAM channels usually are listed a few times, each one with a different audio sub-channel. Some of them are AC3, others are not (not sure if PCM or something else) and others have different language (e.g. Spanish audio, etc.)
However all digital audio not matter if AC3 or not is low volume. perhaps it's HVR-1800 problem and not Cable company (as you observe the opposite scenario on HDTV).

I don't use AC3 filter as it was not working correctly on Vista x64 and causing varying audio offset depending on channel. FFDshow seems to be much better, but harder to configure. In short I don't know how to tell FFDshow to boost volume on QAM channels.

I have not isolated the issue yet, so it's possibel that it exists only in GB-PVR or only in my Cable provider or only on digital tuner of any HVR-1800.

Please people post your thoughts and experience with your setups.

On my side I can try to hook up any QAM channel with WinTV and compare audio loudness against same channel in GB-PVR. Unfortunately I have no other digital TV tuner card nor I have ability to test my hardware with a different cable company.

[feniks]

Good point on the AC3 encoding of QAM. Analog TV has only 2 channel stereo. Look at the properties of your audio decoder and confirm that the speaker arrangement in the decoder matches what you are using. Typically, for AC3, you will have various surround sound speaker configurations to select. I had to change from receiver to TV speakers on my Nvidia decoder to get correct stereo sound. AC3 Filter also works well for me and it's free.

I've done that already. Speakers are correctly setup to 5.1 in my Realtek audio driver and sound loud on all channels when testing with anything else except QAM TV. also FFDshow is set to Dolby mode and plays on either 2 or 6 audio channels depending on audio track hooked to digital channel (not all are AC3).

For me NVidia Purevideo was not able to make audio louder (it was quite the opposite), but it had impact on all channels (both analog and digital), so it didn't have any effect specifically to QAM/AC3. I don't use it anymore, as on Vista x64 it was causing some variable audio offset issues. FFDshow seems to work better for me.

[topperdude]

I also believe this might have something to do with recordings that have 5.1 sound being decoded for playback on 2 speakers as previously suggested.

When my HVR1600 records QAM channels, some shows have 5.1 surround sound while other QAM channels have 2.0 stereo sound. Playing back the shows with 5.1 sound on my computer (which has two speakers) gives the lower volume compared to shows with 2.0 stereo sound recorded by either QAM tuner or the analog tuner. When I playback either recording on the living room TV (through PCH) the audio is correctly decoded by the receiver.

You might want to try the merc82's suggestion of tweaking your settings in the audio decoder to normalize the sound format. I use AC3 filter as well but havent done much tweaking to normalize the sound since most (98%) of my TV viewing is through client devices such as PCH connected to the TV.

Just my $0.02,

HTH,
-Topper

[feniks]

yeah, it's always a thought to play around with all audio driver, decoder, renderer settings all over again hehe. perhaps i will again, but i've done that couple times and tested many audio decoders and all of them have more or less the same issue for me.
moreover i noticed it under two OS's - XP x64 SP2 and Vista x64 SP1. I was unfortunately unable to fire up GB-PVR on Windows 7 x64 beta yet (LIVE TV not working).

i'm not convinced that it is an audio settings problem though.

[merc82]

I have this problem only with QAM on my digital tuner on HVR-1800 (analog tuner works great). I noticed that QAM channels usually are listed a few times, each one with a different audio sub-channel. Some of them are AC3, others are not (not sure if PCM or something else) and others have different language (e.g. Spanish audio, etc.)
However all digital audio not matter if AC3 or not is low volume. perhaps it's HVR-1800 problem and not Cable company (as you observe the opposite scenario on HDTV).
.

feniks, on my cable company all QAM channels I receive are AC3 stereo. If you are referring to the QAM channel list in the channel mapper of the GBPVR config tool I wouldn't relay on this to determine if a channel is AC3. A scan of ATSC channels on my system included channels that didn't state they were AC3 when in fact they were. To determine if a channel is AC3 I'd believe what your HDTV or AV receiver (if you use SPDIF) tell you.

Have you experimented with other AC3 sources within GBPVR such as an ATSC broadcast or video file with AC3 sound? If these sources have a volume output in line with analog TV then I'd say your cable company is messing with the QAM sound. I know my cable company wants everyone to use one of their set top boxes so the sound might be adjusted there.

If after trying these things out you're interested in normalizing the sound level with ffdshow I think the volume or mixer options in the ffdshow audio config tool is the place to go. This should adjust all sound that ffdshow handles so you might want to set up GBPVR to use ffdshow only for AC3.

[feniks]

well said. I am actually suspecting my cable company (evil Comcast hehe ]:->) that it lowers audio volume on QAM channels in order to force "analog" users to get STB which is most-likely pre-programmed to boost QAM or other digital volume. Unfortunately I have no way to prove this theory as i do not own any HDTV or nothing else capable of connecting to TV cable except for my TV tuner card lol

haha, probably you think now "hey look what a freak, in 21st century he doesn't own a TV"... well that's me My central and only multimedia device in living room is my rig used for everything from listening to music, watching TV or DVD, gaming and up to serious professional work.

I think i will mess with ffdshow audio mixer settings and see what comes up and follow suggestion and set it only for AC3 decoding and leave a different audio decoder for classic 2.0 stereo sound.

After work I will give a shot to WinTV just to make sure it's not my GB-PVR setup causing the trouble. The other reasons would be either HVR-1800's poor digital tuner or card not working correctly (unlikely) or Comcast ISP messing with free QAM audio signal strength (very likely).

[mian]

My qam recordings are definitely lower volume than my analog recordings, though not so low as to really present a problem. I just have to crank the volume a little higher with them.

Of course, I should say lower than most of my analog channels. The volume across my entire basic cable lineup is incredibly inconsistent. Channel flipping is very annoying for me. One channel blares, the next you can't even hear what's being said.

I don't know about your problem, but I suspect mine is just normal channel to channel variance.

I also get lots of transport stream errors which affect how many ac3 channels I can actually access in different programs. I assume that is signal issues or driver issues.