PCM vs. Dolby vs. DTS over TOSLINK

[FatStrat85]

I'm continuing an off-topic discussion from the following thread:

http://forums.audioholics.com/forums/showthread.php?t=45286

I have my PS3 connected to my Yamaha RX-V659 receiver through optical digital TOSLINK. I run a 2.1 setup. My receiver down-mixes everything to 2.1 for me.

For music, I have the PS3 outputting 44.1 kHz 2-channel PCM to the receiver. That's great. My question is concerning movies.

I can set the PS3 to output 2-channel PCM. The sound is uncompressed, but I get no LFE channel. Otherwise, I can set it to Dolby or DTS multi-channel. The sound is compressed, but I get a LFE channel. Which to you think is the better option?

If one of the multi-channel formats is my better option, then which one? My receiver reads the bitrate for Dolby as 448 Kbps. Divided between 6 channels, that's less than 75 Kbps per channel. Ouch. My receiver reads the bitrate for DTS as 1536 Kbps. Divided between 6 channels, that's 256 Kbps per channel. That's not bad at all. I was surprised that there was such a big difference between the bitrates of the two formats, because DTS isn't regarded as being clearly superior to Dolby from what I've read. One doesn't seem to be commonly regarded as superior to the other, just different.

From listening tests with MP3s, I don't believe I can discern the difference between a 512 Kbps (256 for each channel) MP3 and an uncompressed Red Book CD. On the other hand, a 150 Kbps (75 for each channel) MP3 can sometimes sound a bit rough with artifacts, etc...

Does DTS and Dolby compression compare to MP3 compression, or is it less efficient? If it's about the same, then DTS would certainly be my best option because it would give me multi-channel output (the LFE channel is all I'm concerned with really) and sound quality that is indiscernible from uncompressed CD audio to my ears. Am I making incorrect assumptions here? What do you recommend?

 

[MDS]

My question is concerning movies.

I can set the PS3 to output 2-channel PCM. The sound is uncompressed, but I get no LFE channel. Otherwise, I can set it to Dolby or DTS multi-channel. The sound is compressed, but I get a LFE channel. Which to you think is the better option?

It's a subtle difference but when you set the PS3 to output PCM it decodes and downmixes the 5.1 channels to 2 channels. There is no longer a dedicated LFE channel as it was folded into the 2 channel mix and the receiver sees it as 2 channel. If you had 5.1 speakers you could then use a matrix decoder like PLII to turn it back into 5.1 (but it will be slightly different than what you'd get if you had the ps3 output bitstream).

When you output a bitstream it is a single stream that contains all 5.1 channels. The receiver now decodes that and sends each channel to its respective speaker but with only 2.1 speakers attached, the receiver also has to downmix. The difference is that the receiver starts with all 5.1 channels and so can route the LFE (the .1 from the DD/DTS track) to the sub.

I prefer to send the receiver the bitstream because it can process it and apply other effects like dynamic compression (aka 'late night mode) that would not be available if you send it PCM.

 

[speakerman39]

It's a subtle difference but when you set the PS3 to output PCM it decodes and downmixes the 5.1 channels to 2 channels. There is no longer a dedicated LFE channel as it was folded into the 2 channel mix and the receiver sees it as 2 channel. If you had 5.1 speakers you could then use a matrix decoder like PLII to turn it back into 5.1 (but it will be slightly different than what you'd get if you had the ps3 output bitstream).

When you output a bitstream it is a single stream that contains all 5.1 channels. The receiver now decodes that and sends each channel to its respective speaker but with only 2.1 speakers attached, the receiver also has to downmix. The difference is that the receiver starts with all 5.1 channels and so can route the LFE (the .1 from the DD/DTS track) to the sub.

I prefer to send the receiver the bitstream because it can process it and apply other effects like dynamic compression (aka 'late night mode) that would not be available if you send it PCM.

Once again MDS very informative and quite helpful.

Cheers,

Phil

 

[FatStrat85]

The consensus seems to be that one of the compressed multi-channel formats would be superior to 2-channel PCM. I've searched online for comparisons of Dolby and DTS. The consensus there seems to be that they are both equal or that DTS is slightly better. Even though DTS has a higher bitrate, it uses a less efficient compression codec than dolby. That levels the playing field quite a bit, giving DTS only a slight and arguable edge. The following link provided a good comparision.

http://findarticles.com/p/articles/mi_m0FXG/is_7_13/ai_63857428

This has made me realize the appeal of the HD audio formats like Dolby TrueHD and DTS-HD. I guess I'll one-day upgrade to a HDMI 1.3a receiver once they become fully standard and affordable.

 

[FatStrat85]

2.1 options?

I have another quick question. Is there any way to output 2.1 PCM from the PS3 to my reciever using the TOSLINK? I don't know if TOSLINK has the banwidth for that extra discrete .1 LFE channel. That would be the perfect solution for me.

Alternately, is there any way to tell the PS3 to output a Dolby or DTS bitstream in 2.1 instead of 5.1? There would need to be less compression if it down-mixed the unnecessary channels in the PS3 instead of later on the receiver. I doubt that's possible, but it would be cool.

 

[Seth=L]

I would use the analog audio output from the PS3 instead of optical. The optical can't pass high resolution 2 channel audio, where the analog outputs on the PS3 can. Since you are only using it for 2.1 I see no reason to use toslink.

 

[Seth=L]

Alternately, is there any way to tell the PS3 to output a Dolby or DTS bitstream in 2.1 instead of 5.1? There would need to be less compression if it down-mixed the unnecessary channels in the PS3 instead of later on the receiver. I doubt that's possible, but it would be cool.

No, that is not possible.

 

[FatStrat85]

I have the 40GB PS3. The only analog output it has is that AV multi out connector thing.