PCM or Dolby
 

Hi
I have a Sony 2.1 sound bar newly arrived for my Sony TV and was wondering what is the best TiVo setting for audio through it: PCM or Dolby? :confused:

Re: PCM or Dolby
 

I'd have thought that you want to connect the soundbar to the TV directly so all sources can use it?

My Sony has PCM, optical and analog outputs for slave speaker systems but only the analog connection uses the TV remote for volume. I have a subwoofer connected to that to bulk up the sound.

Re: PCM or Dolby
 

What he said^^^. This also helps to avoid possible lip-sync issues if the TV is slower to show the video than the soundbar is to produce the audio.

As for Dolby vs. PCM, probably Dolby, but try both and see which works/sounds best.

Re: PCM or Dolby
 

PCM is uncompressed, allowing the decoding (of DTS or various other surround sound formats) to be done by the connected equipment.

Dolby is a compressed output.

If your just talking a soundbar then I doubt you'll notice any difference, but if you have a half decent receiver connected then PCM would be the way to go.

Re: PCM or Dolby
 

but in this case it originates from a compressed source (either MPEG audio or Dolby), so any benefit is lost.

On the contrary, if you have a half decent receiver, it should so a better job of decoding the Dolby than the consumer-grade chip in the TiVo.

Re: PCM or Dolby
 

spiderplant that is incorrect.
PCM is far superior to Dolby via the tivo box, PCM is uncompressed stereo.
Try listening to just 2 chan via a quality system, first use PCM then use Dolby from the tivo box, the sound from PCM is far superior in dynamic range.
The tivo gives 2 options: Dolby Digital and Dolby to PCM, when you select Dolby Digital you get a compressed 5.1 mix, when you select PCM you get the full uncompressed stereo (standard CD quality)

Re: PCM or Dolby
 

Why would you want the stereo output though if you have a 5.1 system?

Re: PCM or Dolby
 

I don't, the original poster has a a 2.1 system that was the question.

When you select Dolby Digital you get a compressed 5.1 mix OR when you select PCM you get the full uncompressed stereo (standard CD quality)

It's a choice, your retort makes no sense to this post.

Re: PCM or Dolby
 

VM transmit their content already encoded as Dolby 5.1 If you select PCM all you are doing is telling the Tivo to convert that to PCM. You aren't getting the uncompressed stream because Virgin dont make that available.

Re: PCM or Dolby
 

Skie: When you chose PCM you get uncompressed CD quality.
When you chose Dolby Digital you get compressed multi chan.

You can't get PCM back from a lossy format, once it's compressed it's lost.

Re: PCM or Dolby
 

He is saying it is already compressed when the TiVo receives it.

So its not going to be fully PCM uncompressed.

My response about 5.1 is valid. IF you were already using a 5.1 system, you wouldn't bother or need to change to PCM for the amp to then convert it to DD again.

Re: PCM or Dolby
 

Yes I agree about 5.1, but spiderplant was saying that there is no benefit to PCM in any case, as it's compressed.
I use an AV receiver and floorstanding main speakers and the quality is better using a 2.0 or a 3.0 set up if I select PCM from the tivo.
If I select Dolby Digital the sound loses some dynamic range and richness, so in my opinion PCM sounds better.
So in my opinion if you don't need 5.1 select PCM for better quality if you have a decent system.

Re: PCM or Dolby
 

Sound always arrives at the TiVo from Virgin in a lossy format: Dolby Digital / AC3 for most of the HD channels and MPEG Layer 2 audio for SD channels and some HD channels (e.g. BBC News and ITV). The MPEG Layer 2 audio standard dates back to the end of the eighties and is easily outperformed by Dolby's AC3 codec.

If you have the TiVo set to deliver PCM to your home cinema system then all you are doing is having the AC3 conversion done in the TiVo rather than in your home cinema system for those channels in Dolby Digital. As Spiderplant said, the TiVo conversion will be inferior to what is capable by the dedicated chips in a more expensive home cinema system.

The TiVo does seem to do the conversion at a higher volume level than you get passing Dolby Digital through to a home cinema system, so it may be that perceptual difference ("richness") that you are hearing. The Dolby format includes extra data on how to optimise downmixing multi-channel sound which not every device will support.

Should note that the TV companies also often process the sound differently between the SD channels and HD channels with greater compression of the SD sound levels - i.e. fewer differences between the loud and quiet bits. Dolby define a standard level for speech in a soundtrack which is considerably lower than traditionally used in TV but allows for loud effects and music in movies. That's another reason why movies on a channel in Dolby Digital sound quieter. Just turn up the volume to appreciate the full dynamic range!

Re: PCM or Dolby
 

I didn't say it was compressed; I said it comes from a source that is compressed.

I also said "try both and see which works/sounds best". If you prefer PCM, that's fine by me.

Re: PCM or Dolby
 

The PCM stream is better quality than the Dolby Digital.
I can play many a gig on Sky arts and the difference in quality from: stereo(2.0) from PCM, to Stereo(2.0) from Dolby Digital, is very noticeable even after adjusting the sound.
This is from the tivo, using HDMI to a Sony AV Receiver, using Tannoy V4 speakers in 2.0 Ch mode. The only difference is the selection of PCM or DD from the tivo.

---------- Post added at 19:41 ---------- Previous post was at 19:37 ----------

The PCM stream is better quality than the Dolby Digital.
I can play many a gig on Sky arts and the difference in quality from: stereo(2.0) from PCM, to Stereo(2.0) from Dolby Digital, is very noticeable even after adjusting the sound.
This is from the tivo, using HDMI to a Sony AV Receiver, using Tannoy V4 speakers in 2.0 Ch mode. The only difference is the selection of PCM or DD from the tivo.
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---------- Post added at 19:47 ---------- Previous post was at 19:41 ----------

Hi spiderplant, yes sorry not trying to be rude or anything, got a bit caught up in the moment.
Yes you are right it is what ever is best for the user.
But this is an intriguing point for me :)

Re: PCM or Dolby
 

All you're really saying is that you prefer the sound of the Dolby Digital decoder in the TiVo to the one in your AV amp. Nothing wrong with that but that's all it is.

Re: PCM or Dolby
 

steveh: If I am receiving PCM from the tivo, and using PCM for 2.0 Chan stereo, I'm not using Dolby Digital.
REMEMBER: The PCM option is for equipment that MAY NOT BE ABLE TO DECODE Dolby Digital.
Did you really think this through?

Re: PCM or Dolby
 

The transport stream that your TiVo receives from Virgin for an HD channel only contains Dolby Digital audio*. It does not contain a separate PCM audio stream. If you choose the PCM option in the TiVo settings then the TiVo will use its internal Dolby Digital decoder to convert that Dolby stream into a PCM stream to send to your AV amp. If you choose the Dolby option then it will instead pass through the Dolby Digital stream to your AV amp to decode instead.

(* Except for those HD channels like BBC News that aren't in Dolby and like the SD channels use MPEG Layer 2 audio instead, which the TiVo will always convert to PCM before sending to your amp. Some also have an additional audio description stream that may not be in Dolby.)

Re: PCM or Dolby
 

steveh: So (only) BBC HD channels and all SD channels are not Dolby Digital, hence the better sound quality using the PCM stream imo.
That's still a lot of channels though, even if you are correct about all the other HD channel streams.
Probably at least half of all available channels on the tivo are not Dolby Digital then.

Re: PCM or Dolby
 

The ITV HD channels are also not DD I believe.

Re: PCM or Dolby
 

Just to be completely clear:

1. The PCM audio that you get out of your TiVo is always converted by the box from a compressed format.

2. There is no PCM audio delivered to set top boxes through Virgin's cable TV network.

3. Dolby Digital decoders can sound different in different devices for reasons to do with cost, age, settings and the kind of device they are. That's what you're hearing.

4. The BBC News Channel in HD does not use Dolby Digital, the other BBC HD channels do.

Re: PCM or Dolby
 

Is it possible that the PCM stream I get from the tivo box that is from a compressed format is of better quality than the Dolby Digital stream that is also from the same compressed format?
Also, on channels that are not Dolby Digital (Like the BBC HD News Channel) Why does the selection of either PCM or DD from the tivo sound different at the AV receiver, if there is no DD option what is the DD selection at the tivo streaming that sounds different to the PCM option?

Re: PCM or Dolby
 

I don't have any knowledge of the TiVo internals but I would have thought it very unlikely there was any difference for non-Dolby Digital (i.e. MPEG Audio Layer 2) channels depending on the audio setting.

The chain is like this...

TiVo set to PCM output:

Channel in MP2 -> TiVo converts to PCM -> Your amp plays PCM
Channel in DD -> TiVo converts to PCM -> Your amp plays PCM

Tivo set to Dolby Digital output:

Channel in MP2 -> TiVo converts to PCM -> Your amp plays PCM
Channel in DD -> TiVo passes DD straight through -> Your amp decodes DD

Dolby Digital gives higher quality than MPEG Audio Layer 2 assuming the same bitrate. However, as I said before the TV companies may do different audio processing on Dolby and non-Dolby channels so they won't sound the same. An average user will be more likely to hear the differences in processing than any differences between the codecs.