TiVo : PCM or Dolby

[johnasimmons]

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?

[heero_yuy]

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.

[spiderplant]

Originally Posted by heero_yuy

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

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.

[Skie]

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.

[spiderplant]

Originally Posted by Skie

PCM is uncompressed

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

Originally Posted by Skie

if you have a half decent receiver connected then PCM would be the way to go.

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.

[mm7000gb]

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)

[Stephen]

Originally Posted by mm7000gb

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)

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

[mm7000gb]

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.

[Skie]

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.

[mm7000gb]

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.

[Stephen]

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.

[mm7000gb]

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.

[steveh]

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!

[spiderplant]

Originally Posted by mm7000gb

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 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.

[mm7000gb]

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 ----------

Originally Posted by steveh

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!

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 ----------

Originally Posted by spiderplant

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.

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