Can anyone explain how digital audio works?

[jsirota]

I've posted here before about various audio problems I've had with my HR10. I do not have any DD5.1 decoder -- all I have for speakers are the two built into my plasma monitor. I connect the HR10 to the monitor through the HDMI cable.

The problem is that when I'm watching a TV broadcast that includes DD5.1 audio, it often sounds crappy to me. It sounds like I'm just not hearing anything that would be on the center channel. It's most obvious with sports broadcasts, where my theory is that the announcers are often primarily on the center channel with the "sounds of the game" on the side channels, and it's as though I cannot hear the announcers over the sounds of the game. We often switch to SD just to make the audio tolerable.

Now, this weekend I borrowed a DD5.1 receiver and hooked it up, just to try to prove or disprove the theory. I hooked up the 3 front speakers plus the sub to this receiver, plugged in the optical link, and changed the settings in the HR10 menu to make it output the DD5.1 audio.

Well, it worked like a charm, and when watching the X-Games last night, I could clearly tell that the announcers were 99% on the center channel. They were barely audible at all on the side channels. However, when watching through the TV speakers via HDMI, I can hear the announcers somewhat, louder than they were on the DD5.1 side channels.

So, what device is responsible for putting those voices on my TV speakers when I disable dolby audio? Does the signal from the network contain BOTH Dolby audio and regular stereo audio? Or does it contain only Dolby audio and the HR10 has to figure out what to send to the TV? Or, is it entirely the job of the TV to take the dolby audio from the HDMI port and figure out what to put on the two speakers it has built-in?

Seems to me that the broadcast cannot contain both dolby audio and regular stereo audio, because if that were the case, I'd be able to hear the announcers better.

So, can someone who really knows explain the technology to me?

BTW, another anomoly happened when I hooked this stuff up. When I first hooked up the DD5.1 receiver, I could hear audio on BOTH the TV speakers and I was also getting the full Dolby surround treatment through the external amplifier. I turned down the TV's volume in order to hear only the new speakers. But then later (after turning things on and off, changing channels a bunch, etc), I turned the TV volume back up, and I was getting no audio to the TV at all when watching an HD DD5.1 broadcast. Can't explain that one.

[TyroneShoes]

Just like analog stereo can send two simultaneous channels, DD and analog stereo can also be sent simultaneously. In fact, DD is rarely sent without also sending the conventional audio tracks as well.

If the source is properly configured, dialog is typically on the center channel, but there are often technical screwups that cause this not to happen. It would be very unlikely that you would get some DD tracks but not others (from a single DD broadcast) unless it were a source issue only. It would be very rare for DD decoding to only get partial tracks and it be due to local connections, your PVR, or your AVR.

Not hearing the conventional audio tracks locally when DD is sent is usually a preferences setting on the receiver, but reboots have also been known to fix this on occasion.

[jsirota]

Thanks, but I still don't understand.

So you are saying that the original source contains both DD5.1 *and* stereo audio, right? Meaning that the audio engineers who put together these broadcasts have to do both.

So what that means is that the fact that I couldn't hear the announcers during the superbowl (HDTV OTA onto HR10-250, HDMI direct to monitor/speakers, but no DD5.1 decoder) means that it was the broadcast's fault, not one of my devices? Apparently no one else was watching the Superbowl in HD but without DD5.1? Am I the only one in the world who has an HDTV but doesn't have a surround sound decoder? Hard to believe. I have not read a single other complaint about this problem anywhere else, which leads me to believe that I've got an equipment problem -- I'm just not sure which piece of equipment I should be concentrating on.

[kdonnel]

Am I the only one in the world who has an HDTV but doesn't have a surround sound decoder?

If you do not have an A/V Receiver doing the decoding then you should connect the HDMI cable and rca stereo cables to your tv.

Your tv does not have a clue what to do with the DD signal since it does not have a DD decoder built in. You will not get any sound on DD only broadcasts if your audio signal processing equipment does not know how to decode the stream.

Nothing is wrong with your equipment.

Here is another thread talking about the same problem.

http://www.tivocommunity.com/tivo-vb/showthread.php?t=307908

[chris_h]

Jsiroto,

Can you give a little more detail around how often this happens? Is it on all HD channels, or just a few? Which specific ones are you seeing it on? I have seen this happen maybe two or three times in the past two years, and I beleived it to be a mixing problem at the source (I think it was probably NFL one time, and a PBS presentation on aquariums the second time, which a later recording of the same program was fine).

Tyrone,
I thought that I had read in another thread that it would be the receiver, in this case the HR10-250 which was responsible for "mixing" the 5.1 channels down to two channels for left and right analog audio (which may not be what the OP is using). Are you saying that an mpeg2 stream with 5.1 channel sound would also include another two channels of plain left/right audio for output on the analog channels? That is how I interpreted your post.

Thanks in advance.

[TyroneShoes]

...,
I thought that I had read in another thread that it would be the receiver, in this case the HR10-250 which was responsible for "mixing" the 5.1 channels down to two channels for left and right analog audio (which may not be what the OP is using). Are you saying that an mpeg2 stream with 5.1 channel sound would also include another two channels of plain left/right audio for output on the analog channels? That is how I interpreted your post.

Thanks in advance.
Not exactly, what I said (or maybe what I meant to say) is that a feed containing DD tracks could include conventional audio tracks as well as DD tracks, not that it always does as a rule. This was directly in reply to the OP's incredulity over both DD and stereo audio coexisting within a single broadcast.

As a DT broadcaster, we actually send both, simply because not everyone is guaranteed to have a DD decoder. For them, stereo audio can't be secondarily derived from DD since they may be unable to decode DD.

While ATSC reception typically includes ASC-3 decoding as a part of the package, many local stations have yet to add local 5.1 DD encoding into their program stream. For FOX affils, for example, DD is built in to the feed they receive from FOX, and they alter that in no way before passing it on to the viewers, so the local station does not need to provide local encoding, especially since DD on localized or even syndicated programming is still somewhat rare.

It can be done a number of ways. Since the OP was somewhat all over the place, I limited my answers to only a portion of what it seemed he might be getting at. It was in no way intended to be comprehensive.

[TyroneShoes]

Thanks, but I still don't understand.

So you are saying that the original source contains both DD5.1 *and* stereo audio, right? Meaning that the audio engineers who put together these broadcasts have to do both.

So what that means is that the fact that I couldn't hear the announcers during the superbowl (HDTV OTA onto HR10-250, HDMI direct to monitor/speakers, but no DD5.1 decoder) means that it was the broadcast's fault, not one of my devices? Apparently no one else was watching the Superbowl in HD but without DD5.1? Am I the only one in the world who has an HDTV but doesn't have a surround sound decoder? Hard to believe. I have not read a single other complaint about this problem anywhere else, which leads me to believe that I've got an equipment problem -- I'm just not sure which piece of equipment I should be concentrating on.
Since you were unspecific about your issues, my responses were likewise unspecific. I did not ever say "this is what's happening with your situation", or "this is how it's always done", I instead gave you clues to areas to look into.

As someone who has posted some of the longest posts on this forum :o , it's a little ironic of me to say this (and I feel a little silly saying this), but I'll go out on a limb and predict that you would receive better answers if you could edit your posts a little better. IOW, try to concentrate only on what might be directly the issue, and try not to leave important stuff out. Your followup added new information about the SB and other things that would have probably guided those who respond a little better. And I understand that this might be difficult when you don't really understand where the problem really is, which is why I limited my response to baby steps, tailored directly to the points I could understand in your original post.

But if anything, I am patient. We can still try to help you, we just need a bit better info regarding your situation, and a little kinder acceptance of our efforts to help. Post back, and good luck.

[jsirota]

Okay, thanks for being patient. I tried to be thorough in the first post but I obviously failed. Let me try again.

My setup: HR10-250 with an OTA antenna as well as the satellite feeds. I have an HDTV monitor with built-in speakers (Maxent MXV3 if it's important) which I connect to the HR10 with an HDMI cable. That's it. I do not have a DD5.1 decoder, either in the TV or connected externally to the HR10.

Normal SD broadcasts appear and sound exactly like I'd expect them to.

But HD broadcasts, especially ones that say that they have DD5.1 audio, rarely sound good. It seems like the mixing is totally wrong. Sound effects are often louder than dialog. In sports broadcasts, like the X-games recently and the Superbowl not-so-recently, I can barely hear the announcers. I have to CRANK the volume in order to hear what should be the loudest stuff, and then, of course, the other noises (like the crowd at the Superbowl) is deafening. It's so bad that we usually end up switching to the SD broadcast over satellite.

Okay, that's the summary of the problem.

The rest of this post is my attempt to explain what I think I've learned about this, that might explain this.

Some HD broadcasts with DD5.1 also include regular stereo audio. Of course, I do not have a DD5.1 decoder, so I'm dependent on those stereo signals included in the broadcast stream. It sounds like the problems I'm having are therefore the fault of those who originally created those stereo channels, at the broadcast source.

But then I'm confused that apparently some HD broadcasts with DD5.1 audio do NOT include regular stereo signals. If that were the case, then would I never hear any audio?

Now, in the original post at the top of this thread I talked about borrowing a DD5.1 decoder and a set of speakers. I did during the X-games (which sounded awful when watching in HD) to just see if my theory was correct that I simply was not hearing the announcers because the DD5.1 feed had them all on the center channel, and my lack of a decoder meant that I couldn't hear the center channel. Well, sure enough, the announcers were 90%-100% on the center channel. However, WITH the DD5.1 setup, I really couldn't hear the announcers on the side channels at all. WITHOUT the DD5.1 setup, I COULD hear the announcers on my TV speakers, but just not loud enough to be heard over the crowd noise.

That's about as thorough and clear as I think I can be. Did it help anything?

[Budget_HT]

jsirota,

Here are two things you can try that have worked for me, using an HD TiVo connected via HDMI to an HDTV that cannot decode DD5.1:

1. Set the HD TiVo for DD 5.1 off. Press the DirecTV button at the very top of your TiVo remote to start this path into the needed setting: DirecTV Setup>>Settings>>Audio>>Dolby Digital, then select "No, play standard audio." As I understand it, this effectively turns off DD 5.1 within the HD TiVo and instead sends stereo audio out over the HDMI connection (I think as PCM digital).

2. Hook up separate analog audio. If your HDTV supports it, make a separate L+R analog stereo audio connection (i.e., red and white RCA connectors for audio on the TiVo and the same or a miniature stereo phone plug on the HDTV. Then set the option in your TV to use the analog audio instead of the digital audio. My TV has this provision in case I am feeding it a DVI signal (e.g., from a computer) that lacks digital audio and needs separate analog audio to work.

Both of these approaches result in stereo audio being sent to the TV. The second option does not care whether the HD TiVo is set to yes or no for DD 5.1 because all analog audio is stereo out of the HD TiVo.

Regarding what comes from the broadcast station for HDTV audio, I had a different impression than that described by Tyrone. Most commonly, I see two audio formats being sent by the DTV stations: either DD 5.1 or DD 2.0.

I know there are also secondary audio capabilities available in the ATSC standard, such as for a different language or other alternate audio. But selecting between the choices is not user friendly on the HD tuners that I have used, and I don't recall even seeing that capability on my HD TiVo (although admittedly I did not look yet--I will look when I can).

Back to the primary audio. My understanding is that the HD receiver either passes through the DD 5.1 (to a digital output) or it downmixes the DD 5.1 to 2-channel stereo audio, and I suspect with matrix-encoded center and rear surround channels that can be decoded by a Dolby Pro Logic II decoder. If not, the DD 5.1-capable receiver simulates the same thing somehow.

Primary DD 2.0 audio is already stereo, sometimes with matrix-encoded center and surround. This I believe is sent through as is to both the digital and analog outputs.

All that said, using my HD TiVo with my HDTV on either scenario above gives audio without losing the center channel content.

Good luck with your issue.

[jsirota]

Thanks. Your #1 option is exactly what I'm doing right now. That setting has to be off, otherwise, I get no audio on broadcasts with DD5.1.

About option #2, I'm pretty sure that on my TV, if the HDMI input is used, it will only accept audio from the HDMI connector. There is no menu choice to force it to use a different audio source. So I think I'll try a variant of that suggestion to see if it sounds any different. I'll hook up the component output of the HR10 to a component input on the TV, with just regular RCA cables for the audio. That might produce a different audio mix than occurs via HDMI.

So you and Tyrone differ on whether or not the HR10 "downmixes" (is that a real word?) DD5.1 audio to regular 2-channel stereo. If it does, then my problem COULD be the HR10's fault, except that no one else seems to be complaining about it. At least, it sounds like the problem is not the fault of the TV. It must be either mixed poorly at the source if the source stream contains both DD5.1 and stereo, or, if the stream does not contain both formats, then it must be the fault of the logic that does the "downmixing" (but again, I wonder why I seem to be the only one with this problem.)

BTW, the HR10 does have the ability to select those alternate audio channels such as those used for secondary languages. On the info screen for the current broadcast (as you get by pressing the "right" arrow when watching), on the right side of the screen where you can switch to the other tuner, there is a little dolby icon. It is yellow sometimes. When it's yellow, if you select it, it shows you what alternate audio choices are available and allows you to select them.

[TyroneShoes]

...Regarding what comes from the broadcast station for HDTV audio, I had a different impression than that described by Tyrone. Most commonly, I see two audio formats being sent by the DTV stations: either DD 5.1 or DD 2.0.

...My understanding is that the HD receiver either passes through the DD 5.1 (to a digital output) or it downmixes the DD 5.1 to 2-channel stereo audio, and I suspect with matrix-encoded center and rear surround channels that can be decoded by a Dolby Pro Logic II decoder. If not, the DD 5.1-capable receiver simulates the same thing somehow...
I now see that I have possibly confused the issue by using unclear terminology, and I apologize for that. I should probably not just say "DD" and assume that covers only 5.1 (although that is all anyone on the forums is really interested in for DD), and I probably should not refer to stereo digital tracks which may or may not be AC-3 encoded as "conventional audio tracks", when that in some people's mind's could also mean analog audio, stereo or otherwise. I'll make a mental note to be more careful.

When a TV station provides only 2 channels on its DT feed, that is indeed AC-3 encoded audio, which would be equivalent technically to DD 2.0, or at least a feature-limited duplicate of DD 2.0. Of course that is quite often upconverted from "conventional audio" from the SD feed. That does not limit a DBS provider to sending additional tracks for whatever purpose on sat HD channels.

Now that I have digested the OP's posts a bit more carefully, it sounds like he is saying that the 2-track playback is only bad when the source is DD 5.1, which seems very weird, indeed. It makes me suspect that the HR10 is not extracting the proper two channels for 2-track playback.

[jsirota]

Now that I have digested the OP's posts a bit more carefully, it sounds like he is saying that the 2-track playback is only bad when the source is DD 5.1, which seems very weird, indeed. It makes me suspect that the HR10 is not extracting the proper two channels for 2-track playback.

That's exactly right, we only notice bad audio on HD programming, and although I'm not certain (because I don't have the equipment), I think it's only on HD broadcasts that are DD 5.1.

So now we think this behavior could be caused by a faulty HR10?

[chris_h]

That's exactly right, we only notice bad audio on HD programming, and although I'm not certain (because I don't have the equipment), I think it's only on HD broadcasts that are DD 5.1.

So now we think this behavior could be caused by a faulty HR10?

My vote is a definate maybe. But I still want to see your answers to my questions above before finalizing my ballot. I also want to know if you hear any difference when you turn on DD at the HR10-250 (yes, I know this is counter-intuitive, but it may be a good data point).

I can never understand why people don't put their city in their forum profile. If I knew you were near Fair Oaks, CA I might be tempted to lend you my known-good spare HR10-250 to see if that makes a difference.

[jsirota]

When I turn on the DD setting on the HR10, I hear nothing on the TV when the broadcast includes DD5.1. So that's not an option at all.

As for your other questions: my wife swears that ALL HD broadcasts sound horrible, but to me it's really only noticeable on things with a lot of background noise. Dialog during a standard NBC drama seems okay to me. But sports DEFINITELY have this problem, and even network shows like CSI that use a lot of music tend to cause the dialog to get swallowed.

It happens on both OTA stations and DirecTV HD broadcasts (like ESPN-HD).

But I regret that I haven't kept a log of all of the shows that we notice it on.


Sorry about the location. I'm near San Jose. Not too far away, but too far for the experiment ...

[Budget_HT]

Here is a long shot.

The symptoms you describe could be the result of your two stereo speakers in (or connected to) the TV being wired out of phase (i.e., opposite polarity connections). This could cause an acoustic cancellation of most of the virtual center channel which is essentially anything that is fed equally to both the left and right channels. In the old hifi days, this tended to affect the bass frequencies more than the mid range and highs, but if your speakers are located fairly close together it could "hollow out" voices and other sound in that "virtual center" channel.

On some HDTV LCD and plasma units, the wing speakers can be detached and not used, meaning there is some form of external connection for the speakers. If you have such an external connection you could verify that the speakers are both connected with the same polarity.

I told you it was a long shot.

Then again, this should affect all audio, not just audio from DD 5.1 programs.

I have 2 HD TiVos and I have not had your problem with either of them. I will be interested in your component video + analog audio test results.

On more thought: Does your TV have any audio processing settings, like a wide or panorama setting that simulates wider stereo separation or simulated rear channels? If so, try defeating any such processing and go with plain, unprocessed audio. Some of the simulation capabilities create strange results depending on the type of audio signal sent to them.

[chris_h]

I tend to agree that Dave's idea is a long shot. Another thing to try, if your speakers do not have external connections, see if there is a balance control built in to the TV, and shut off one speaker.

[jsirota]

Thanks for the help, everyone. Here's an update after a few experiments.

Experiment #1: hook up RCA audio jacks alongside the HDMI port. Enable DD on HR10. Still no audio at all. Failed.

Experiment #2: use component output instead of HDMI, w/DD disabled. Sounds exactly the same. Failed.

Experiment #3: use component output instead of HDMI, w/DD enabled. Interestingly, now get audio to TV and optical at the same time. Previously, w/DD programming and DD enabled, no audio was sent to TV. But, audio on TV sounds exactly the same. Failed.

BTW, the speakers on my TV are not detachable, so no ability to check the polarity of the wiring. And my although my TV does have the ability to simulate surround sound, that feature was always disabled. Enabling it changed the tone of the audio but not the volume of the announcers on sports broadcasts.

I believe the only solution is to buy some sort of DD5.1 decoder/surround-sound box. This will not please my wife, but I really want to watch HD programming and have it sound decent (as good as the SD broadcast of the same content), so I guess this is what I will have to do.

[TyroneShoes]

I recommend against using the speakers within the display as part of the audio system, for a number of reasons. I would just turn local audio in the display completely off, and use a AVR and matched speaker systems for all 5 (7) locations. It is much easier to control, and gives a much better end result.

The phase issue crossed my mind, too, as well as the possibility that some of the speakers may not be connected to the proper outputs.

The best way to wire speakers is to tie a knot in the positive lead at both ends, which will guarantee that they don't get swapped. An old Doobie Brothers roadie/guitar tech showed me that one.

The other trick he gave me is to use a 9v battery to identify speakers and check phase. Disconnect both leads from the amp, click the battery on the wire repeatedly, and the proper speaker will click back at you, audibly. To really check phase (rather than assuming the +/- legend is always correct on the speaker, which it sometimes isn't) have someone, such as the nearest 10-year old, watch the speaker cone while you click the battery on and off repeatedly with the + terminal on the battery going to the + lead, and the - to -. If the cone moves toward the front of the speaker when the battery is connected, the wiring is phased properly. Otherwise, it is out of phase.

I recommend jumping through those hoops first to rule out wiring problems, and then you will have narrowed things down.

If you are really looking into a DD decoder, I recommend the JVC digital amps highly, such as the D401 or D701. You can get a 401 for about $350 on line, and it includes HDMI upconversion and 7 channels of 110 wrms power. Much better than the $1500 Yamaha it replaced.

[jsirota]

It must not have been clear that I'm not an audiophile. One of the reasons I bought a display with speakers is exactly so that I didn't have to have a bunch of other speakers around the room, not to mention another device attached to the Tivo.

We're just not into "home theater." We pretty much just watch TV. Rarely watch movies at all, either on DVD or from DirecTV. That's why it's so annoying that it appears that the solution to this problem is to buy more audio equipment.

And as far as wiring, I'm inclined to trust that the internally-wired speakers in the TV are wired correctly (because I don't really feel like taking the TV apart). There are no external speakers in the equation here.

[TyroneShoes]

Well, that somewhat narrows things down to the HR10 or the TV. You could replace one or the other temporarily to find out which. Schlep your HR10 into the bedroom and connect it to that TV, and play back something that gave you a problem in the original setup. If the problem stays in the living room, that's probably where you'll find it. Or vice versa.

[jsirota]

I feel a little silly for never thinking of that! I don't have another HDTV, but I should be able to figure it out with an SDTV.