AC3->DTS, AC3->Dolby, Any Point with a 2 Speaker Setup?

[photoshop]

Hi,

I recently got a Sony DGS820 amp which is 7.1 capable of handling the latest HD Audio formats.

Now, i ONLY have 2 floor standing speakers (hoping to get a sub and a center soon).

My HTPC Is capable of sending audio and picture over its onboard HDMI socket and it does a pretty good job.

My Question is this: Is it worth me sending over un-decoded DTS 5.1/Dolby Digital 5.1 sound to the amp for decoding?

When i tick the option in AC3Filter to use SPDIF my amp lights up with "DTS 3/2.1" or "Dolby Digital 3/2.1" (depending on the .mkv file) but when i un-tick it i get "Linear PCM [48]"

The difference is this; When the amp lights up with DTS/Dolby i have to turn the volume to around 25 but when it says Linear PCM i only need to turn it up to around 10-12. I have to say its more bass'er when not using the SPDIF option and the background soundtrack is more evident.

Could someone please explain to me what is going on?

* Should i be ticking the SPDIF option in AC3Filter when i only have 2 front speakers?
* Am i benefiting anything by using SPDIF and having DTS/DOLBY 3/2.1 lit on the amp???

My personal thinking is that i shouldn't be using it but im a novice as i only got my 1st AV amp less than a week ago so im a little confused and i want to get the best out of my setup

 

[kennyhkw]

Seeing as u only have 2 spks then u should b using Linear PCM.

If u use SPDIF then it will send the 5.1 signal to the amp and the amp will think u have 5 spks and a sub connected.

Basically the front 2 spks will only play the left and right channel sounds.

Linear PCM means the 5.1 track will be down mixed to 2.0 so you can use it with only 2 speakers.

When you eventually upgrade to 5.1 spks then set it back to SPDIF and enjoy!

 

[csmager]

The reason the volume is quiet is that most of the front sound (dialogue etc) will come from the centre speaker - which you don't have. It needs downmixing to 2.0, or you're missing most of the sound.

 

[Eriedor]

There shouldn't be any difference in the sound between pcm or dd, they are merely different methods of transporting audio. However in this case it sounds like your PC audio is set to 2.0, therefore as 5.1 PCM cannot fit down a spdif link it is being downmixed down to 2.0. However i would bet your amp is setup to 2.1 so when it decodes the 5.1 DD signal it downmixes it to 2.1, hence you are losing the bottom end of the audio signal.

DD will be quieter than pcm because pcm has likely been amplified by your HTPC before being sent to the AMP, where as DD will not have been because it is an encoded bitstream.

/edit to answer your question, absolutely yes send DD and DTS over spdif, as it means the amp will receive the pure 5.1 signal straight from the DVD. PCM will always be downmixed as spdif doesn't have enough bandwidth for 5.1 PCM, and you never know whether it's been messed with by your HTPC.

 

[photoshop]

I've configured the amp and it knows i only have 2 front speakers. Shouldn't it be down mixing the received stream to 2 Channel?

With LPCM the amp just shows L/R speakers with a box around them. With DTS/Dolby it shows L/R/C/R1/R2/Sub but only the L/R have a box around them. Does this mean that the amp is only playing the sounds that were destined for the FL/FR speakers? So im missing parts of the soundtrack that are destined for the C/R1/R2/Sub??

Would this apply to my PS3 also? Do i need to set that to LPCM aswell?

 

[photoshop]

There shouldn't be any difference in the sound between pcm or dd, they are merely different methods of transporting audio. However in this case it sounds like your PC audio is set to 2.0, therefore as 5.1 PCM cannot fit down a spdif link it is being downmixed down to 2.0. However i would bet your amp is setup to 2.1 so when it decodes the 5.1 DD signal it downmixes it to 2.1, hence you are losing the bottom end of the audio signal.

DD will be quieter than pcm because pcm has likely been amplified by your HTPC before being sent to the AMP, where as DD will not have been because it is an encoded bitstream.

/edit to answer your question, absolutely yes send DD and DTS over spdif, as it means the amp will receive the pure 5.1 signal straight from the DVD. PCM will always be downmixed as spdif doesn't have enough bandwidth for 5.1 PCM, and you never know whether it's been messed with by your HTPC.

You missed my point mate. Im not using a physical SPDIF output. The only link between my HTPC and the amp is a HDMI cable.
When i select SPDIF output in AC3filter it sends the un-decoded audio over the HDMI lead and thats when DTS/Dolby Digital light up on my amp. When i tick the SPDIF option im just telling the HTPC not to decode the audio and just send it as it is to the amp. It goes over the HDMI connection.

 

[Chris1712]

I run a similiar setup, only with optical.

What I tend to do is, in AC3Filter, downmix to 2.0, with a boost on the centre channel/dialogue and send it as 48khz LPCM. If its a 2.0 track anyway (old tv shows) I'll leave it alone and use SPDIF passthrough.