PCM vs Dolby Digital

[admin_exported]

I'm a bit confused by this subject and hope somebody can educate me.

I read in this forum and April What HiFi that PCM is far better quality than DD or DTS because it is uncompressed (unless it is one of the bluray formats - True HD or DTS Master HD). However, when trawling through the EPG in Sky HD it seems that the HD channels make a point of saying that this program has a DD soundtrack. The SD programming has a PCM soundtrack according to my Onkyo receiver.

What is going on here? If PCM is uncompressed then why do HD channels and DVDs etc carry a compressed soundtrack and seem to be quite proud of doing so? Is the SD Sky carrying "more" sound data than HD?

 

[radovantz]

I think PCM system in the receiver's processing section is originally designed to deliver PCM signal from digital input. In case, this section also can be used for stereo, dolby digital & dts.

Since PCM encoded data need more capacity that DVD cannot offer, we use Dolby Digital & DTS as alternative while waiting new technology like BD entering the market

 

[nads]

check your ibfo on the amp. PCM is just uncompressed sound while DD/DTS is compressed. BUT neither has to be 5.1 the SD PCM might just be 2 channel while the DD on HD might be 5.1.

 

[The_Lhc]

anchorman_02:
I'm a bit confused by this subject and hope somebody can educate me.

I read in this forum and April What HiFi that PCM is far better quality than DD or DTS because it is uncompressed (unless it is one of the bluray formats - True HD or DTS Master HD). However, when trawling through the EPG in Sky HD it seems that the HD channels make a point of saying that this program has a DD soundtrack. The SD programming has a PCM soundtrack according to my Onkyo receiver.

What is going on here? If PCM is uncompressed then why do HD channels and DVDs etc carry a compressed soundtrack and seem to be quite proud of doing so? Is the SD Sky carrying "more" sound data than HD?

No it isn't, you're getting your PCMs mixed up, or rather you haven't realised that PCM can be any number of channels. PCM soundtracks on Blu-Ray are typically 5.1 or 7.1, however PCM can also be two-channel (stereo) and this is what most Sky channels deliver from the optical output. As you've seen it's possible for Sky to deliver Dolby Digital 5.1, however it's not possible for Sky to deliver any HD multi-channel soundtrack, the satellite signal just doesn't have the bandwidth required to deliver DD TrueHD or DTS HD Master, never mind multi-channel PCM.

 

[Anonymous]

OK this makes some sense to me. So the fact that I can hear surround sound when listening to an SD program with PCM soundtrack is down to my receiver just generating a surround track right?

Does the receiver do this from a "best shot" program or is there some sort of surround data embedded in the 2 channel PCM signal? I remember that early surround sound tracks had an "out of phase" signal which the amp processed.

Thanks for your patience!

 

[The_Lhc]

anchorman_02: OK this makes some sense to me. So the fact that I can hear surround sound when listening to an SD program with PCM soundtrack is down to my receiver just generating a surround track right?

Yup.

Does the receiver do this from a "best shot" program or is there some sort of surround data embedded in the 2 channel PCM signal? I remember that early surround sound tracks had an "out of phase" signal which the amp processed.

Yeah, Dolby Pro-Logic, on the Sky Movie Channels it's usually the default if DD5.1 isn't being broadcast.

 

[Anonymous]

Thanks