BUG REPORT: PCM digital audio not working

[Bogney]

My audio system can not accept a Dolby Digital signal. Therefore I operate all my sources in the PCM digital mode. When I set my 921 to 'PCM Only' it seems to still output a Dolby Digital signal. I hear the loud crackling sound indicative of a Dolby Digital signal being fed into a PCM only decoder.

Technical support had me try the usual things with no change. They then concluded that I have a defective unit and the dealer must swap it out. Before I go through that, will somebody please verify that PCM works on their 921.

Thanks,
Bogney

L142HECD-N
120B
F051

[Dualtriamp]

I have the exact same problem, they are wanting to RA the receiver.

[Slordak]

Have you folks (or others) seen a problem where the way the 921 changes between Dolby Digital and regular PCM over the optical audio output causes the stereo receiver to have issues with the audio dropping out?

On my old 508, I could change between channels with no Dolby Digital (e.g. Food Network) and those with 5.1 channel Dolby Digital (e.g. HBO movie w/ DD) and the digital optical bitstream happily changed formats without a hiccup. However, on the 921, something which is being done to the optical output signal sometimes confuses my stereo when changing from a dolby digital station to a non-dolby digital station. When this happen, the stereo has no audio output until one switches the inputs (to use a different input, or to use the analog input and then back to the digital).

This can be quite frustrating, and is probably a combination of whatever the 921 is doing differently and how my stereo receiver handles the switch. Does it send garbage over the link during the long delay when switching channels? Does it not clear out its digital transmission buffer? Whatever the 508 was doing, my stereo handled it without issue, so it might be preferrable to implement this the same way on the 921, if possible!

[Dualtriamp]

Response from DISH,

I understand the problem that you are having, and while I haven't had the opportunity to replicate this issue, it has become evident on another new HDTV receiver that was recently released. I am afraid that at present this may be oversight in the software design of the receiver, but fortunately it is something that may be corrected through future software releases. The logic is that anyone using optical digital output will always want the highest sound quality available and while the menu system supports a way to contain even the digital audio output to two channels, it seems that the software will not allow it. The other side of the issue is that this would likely work if the output were going to an auto or manual switching Dolby Digital A/V receiver. I will begin work on this issue tomorrow. Some of the assets I will need to research this in depth are not available this late in the evening. I will look forward to finding you a resolution for this problem.

[Slordak]

Dualtriamp, it's unfortunate that the menu setting is effectively ignored and the receiver continues to do more or less as it pleases. In your case, it definitely needs to honor the setting, since the entire reason the setting is present is for situations where the stereo cannot accept a full Dolby Digital bitstream.

In my case, where the stereo receiver is auto-sensing/auto-switching, I use the mixed DD/PCM option, but still have problems as the 921 is apparently not doing a clean switch or is otherwise causing the stereo to mute the bitstream sometimes when changing channels. Hence, this problem may be more involved than just a 2-channel down mix, it may be a problem with the way the 921 switches and handles optical output streams in general.

[Bogney]

For the record, the 1.46 software has not cured this problem.

Low level tech support still says this is a hardware problem. I do not believe them. Anyway to find out for sure if this is a recognized software problem?


Edit: Just to clarify, I am referring to the problem where the 921 will not convert Dolby Digital Audio to a PCM signal when PCM only is selected in the 921's menu.

[SimpleSimon]

I have similar problems with my Sony STR-DE695. Sometimes the audio will just drop out and a skip-back will get the 2 boxes back into sync. Maybe you could try that and see what happens?

Anyway, as for Dish Cust. Supp., I gave up trying to get them to listen all the way back when the DishPlayer was new. Maybe 1 in 10 or a 100 or them even know the difference between hardware and software. Hate to be so negative, but after about 20 years in both hardware and software tech support, I think maybe my opinion is not so humble as the saying goes.

From reading the posts here, except for some of the more subtle points deep in the boxes guts, most of the members implicitly know whether a problem is HW or SW.

So, all that being said, IMO the problem you're seeing is NOT likely to be a hardware issue, and even if it's a hardware design flaw, they can probably do something about it with the wonders of software. :)

[Slordak]

So in addition to Bogney's report that L146 did address the problem with the receiver not wanting to down-mix Dolby Digital content to PCM audio, I can report that L146 did not make any difference in the general way which the 921 glitches or cuts out the optical output signal. I had thought since they were making some tweaks in this area (i.e. to disable the output when the receiver is off), they might have fixed other problems here at the same time, but this is apparently not the case.

I am still able to reliably reproduce the problem where I watch a Dolby Digital 5.1 or 2.0 channel, then change to a non-Dolby Digital channel, and the optical audio appears to cut out. The 921 is sending the audio for the new channel, and I know this because I can toggle the stereo receiver input selection back and forth and the audio resumes. Thus, it is something the 921 is doing in terms of either glitching the output (i.e. briefly sending garbage over it) or otherwise doing something to the optical signal during the channel change which causes the stereo receiver to mute the connection. Hence, most people won't see this problem since their stereo probably handles this momentary signal issue differently.

I have never seen this happen with any of my other optical audio sources (connected to the same optical input on the same stereo receiver), including a Dish 508, a Sony PS2, and a Microsoft X-Box.

[SimpleSimon]

I get occassional audio dropouts, but a skip-back lets me hear the audio (un;less the dropout was due to a momentary LOS - generally detectable by seeing some pixelation immediately after). My guess is that something is getting confused in the audio bitstream, and the programmers will find it eventually.

As for PCM vs. DD, I'm set to Line Mode. and DD/PCM. My Sony STR-DE695 displays the encoding briefly whenever it changes, and I've seen all the variations at one time or another. PCM 48 is typical on SD channels. No idea what would happen if I set the 921 to DD-only.

[David_Levin]

My ancient DD receiver cannot be forced to activate Pro Logic when receiving an DD 2.0 signal. On DD 2.0 DVDs the receiver automatically flips to DD 2.0 w/ Pro-Logic, but on the Sat feed this doesn't happen (something with flagging I suppose).

My work-around with the 508 was to change to PCM. But, I'll agree with the others, that the 921 does not down convert DD to PCM. So, now I usually flip to the Analog Outputs for DD 2.0 source (until I get a new receiver).

[Slordak]

OK, so essentially we have two separate optical output problems:

1) The 921 does not do a proper downmix of Dolby Digital content to PCM when set to "PCM Only" mode.

2) The 921 sometimes glitches or drops the signal over the optical output, causing audio drop-outs on some stereo receivers.

Between the various folks in this thread, we've gone into some detail about both of these problems. It would appear that this section of the 921 software needs to be revisited by one of the developers, to see how the mixing is being done and how the switching between DD and PCM is being done.

[Slordak]

Bump. Are people still having audio problems with L180?

Is anyone experiencing random audio drop-outs when watching either "live" or previously recorded content? On the analog and/or digital output?

[Bogney]

The 1.80 software has not cured the problem where the 921 will not convert Dolby Digital Audio to a PCM signal when PCM only is selected in the 921's menu.

[SimpleSimon]

The 1.80 software has not cured the problem where the 921 will not convert Dolby Digital Audio to a PCM signal when PCM only is selected in the 921's menu.
I just confirmed this myself. There is NO re-mixing occurring that I could find.

In addition, the Menu-4-4 DD/PCM option doesn't seem to work.

If you set it to DD only, and the content is PCM only, no audio is output. Therefore, no mix is occurring, but the option works.

If you set it to PCM only, and the content has DD, the DD is still output.

Note that the help for the Menu-4-4 screen does NOT say that the audio will be converted, and even implies that it won't.

[Bogney]

Note that the help for the Menu-4-4 screen does NOT say that the audio will be converted, and even implies that it won't.From pages 84 and 85 of the online manual:

"PCM Only - Select this option only if the stereo system or amplifier
cannot decode Dolby® Digital signals."

There is also a chart that says that there is a PCM down mix of Dolby Digital signals when PCM only is selected.

[Slordak]

The "Dolby Digital Only" option doesn't really make any sense, in that there shouldn't be any stereos/AV receivers which can successfully decode Dolby Digital but which can't handle uncompressed PCM audio. Plus, it would require the 921 to do a pointless 2-channel "Dolby Digital Encode", so let's assume that this option is probably not appropriate and should be removed.

That leaves us with two options, "PCM Only" and "DD/PCM". The former is, as was indicated, for stereos which do not support Dolby Digital. In this case, the device is expected to do the downmix to PCM before sending it out over the optical output; this is the way it works for DVD players and other source devices. To treat this as "PCM Only means we just drop DD audio and do nothing with it" is silly. If the 921 hardware cannot decode/down-mix the Dolby Digital audio itself, it should be sending the other audio feed on that channel, i.e. the decoded MPEG 2-channel audio (which it would normally send over the analog outputs) streamed as PCM.

[Slordak]

Anyhow, so I think we're in agreement that the "PCM Only" option is broken as it currently stands. This is good information to find out, as Mark can note this as "Still being broken" on the bug list.

However, I am also interested to find out more about my particular audio problems, to know if anyone else has experienced these. These are:

A) The problem where one is watching a Dolby Digital 5.1 or 2.0 channel, then changes to a non-Dolby Digital channel, and the optical audio appears to cut out. The 921 is sending the audio for the new channel, and I know this because I can toggle the stereo receiver input selection back and forth and the audio resumes. Thus, it is something the 921 is doing in terms of either glitching the output (i.e. briefly sending garbage over it) or otherwise doing something to the optical signal during the channel change which causes the stereo receiver to mute the connection. Hence, most people won't see this problem since their stereo probably handles this momentary signal issue differently. This never happened on the 508 with optical output, using the exact same stereo setup.

B) An issue where the audio just disappears for a second or two (and then comes back), but with no video degradation or pixelation in any way. I had thought that there might be a hard drive issue with my 921 (starting from Sunday), but aren't video and audio stored together, so that if the drive had an issue reading a particular piece of data, both would glitch? I never saw this problem before L180, so I think it might be related to the new software. The odd thing is I can reproduce the dropped audio by rewinding and playing that piece back, i.e. this can happen while watching "live" TV, and I can rewind past that point and play it back again, and the audio drops out at exactly the same point in time. What the heck could be causing this? Has anyone else seen this on L180?

[Slordak]

Anyone want to comment on either my (A) or (B) above for L182?

I'm still experiencing the same issues I am before. I might just get a new stereo A/V receiver which is more tolerant to the 921 glitching the line (problem (A) above), since I don't think many other people are having this problem. Still, it was a $450 A/V receiver when I bought it and I don't have any other issues with it, so I'd hate to replace it just to deal with a 921 quirk.

[Mark Lamutt]

Nothing has been done to fix this, and to be honest with you, it's not going to get worked on for some time to come. It just doesn't affect enough people to be anywhere near the top of the priority list, compared to the other bugs that are being worked on.

I know it's not what you want to hear, but you do have the option of using analog RCA cables to bypass the problems that you're having currently with the optical output. It may have been a $450 receiver when you bought it, but if it doesn't support DD audio, then it's not worth much anymore. I had a Pioneer DPL receiver for a very long time that I resisted upgrading that I loved, but finally had to bite the bullet and do the upgrade because it just couldn't do what I needed anymore. Yes, the 921 does have an issue with this, but wouldn't you really be better off in the long run upgrading your receiver anyway? 5.1 or better yet 6.1 sound is absolutely worth the upgrade.

[Slordak]

Unlike some of the posters earlier in the thread who don't have Dolby Digital support and need a PCM down-mix (which the 921 is not providing), I am not actually in the same boat. My system is fully Dolby Digital 5.1 compliant (it's a JVC RX-1024VBK) and I have no problem enjoying the Dolby Digital sound.

Instead, my problem is related to the 921 doing something to the digital audio data stream which confuses the stereo receiver and makes it squelch the input. See my description above for (A). This only happens when I switch from a channel which has Dolby Digital to a channel which does not have Dolby Digital (e.g. switch from HBO-HD to Food Network). When I arrive on Food Network, I have no audio. My audio returns if I turn my stereo receiver off and back on, or if I toggle inputs on it. So folks would probably blame my stereo, right? But this same thing has never happened with my 508, which I had hooked up identically.

Hence, during the switch from a Dolby Digital program to a non-Dolby Digital program, the 921 is doing something non-standard to the digital bitstream; I don't know what, but whatever it does makes my stereo say "Whoa, that's no good, better not listen to that input anymore". It's definitely unique to the 921; none of my other input sources hooked up over optical cause this.

[Mark Lamutt]

Ah, sorry about that then. I misread your post.

[SimpleSimon]

My 921 is doing something at least similar - that is, 'glitching' the optical audio.

My Sony STR-DE695 will display the stream type ('PCM 48' and 'DD 3.2/1' are typical) whenever a data stream 'starts'. I can obviously produce this effect by simply pausing the playback, but it also occurs on a random basis for no known reason - no dropouts or anything like that.