Well, I haven’t kept up-to-date with the PS3 firmware recently, this one is added retrospectively.
Firmware 3.30 was released on Apr 22, 2010, and the major updates are support for 3D gaming and a hidden feature: Bitstream (Mix) option for people who are still using optical out with a legacy ac3/DTS receiver.
The most basic feature for Bitstream (Mix) is to provide full sound for button click and PIP secondary audio. But there’s more to it, the most beneficial thing is the ability to playback LPCM 5.1 tracks encoded in DTS 5.1 in real time. Before this update, you will never get the surround sound out of LPCM 5.1 since optical output is only capable of 2 channel LPCM, but now you will at least get the 5.1 full information. This is equivalent to the “Auto mix based on source audio” option provided in Totalmedia Theatre 3 long time ago.
PowerDVD has also provided such mixing, but it’s only limited to AC3/DTS mixing.
“Auto mix based on source audio” is a more elegant way to mix the surround sound, it differs from just AC3/DTS mixing which just lumps all audios into ac3 or DTS.
These are the behaviors I have observed:
For any 1 channel sources:
Always expands to LPCM 2.0
For any 2 channel sources:
LPCM 2.0 - decodes/retains to LPCM 2.0*
Dolby TrueHD 2.0 - decodes to LPCM 2.0
DTS-HD MA 2.0 - decodes to LPCM 2.0
(while if AC3/DTS mixing is chosen in PowerDVD or TMT3/5, these audio will be mixed into ac3 2.0 or DTS 2.0 regardless)
For the LPCM 2.0 source here, I’m not sure what PS3 exactly did, since in LPCM mode, the button sound can be heard regardless if it’s decoded or in original form. I’m guessing it’s more likely to retain the LPCM 2.0 rather than decoding for simplicity, but I could be wrong.
For any 5.1 channel sources:
LPCM 5.1 - compresses as DTS 5.1 and bitstreaming in real time (biggest benefit)
Dolby TrueHD 5.1 - compresses as Dolby Digital 5.1 and bitstreaming in real time
DTS-HD MA 5.1 - compresses as DTS 5.1 and bitstreaming in real time
Any button sound and PIP secondary audio will be mixed in.
I believe for audio more than 5.1 channels, they will be downmixed to 5.1, then compressed and bitstreamed as well. as for why Dolby TrueHD goes to Dolby Digital rather than DTS which is what I preferred, I think it maybe due to a license constraint? Also I have no way to determine what kind of bitrate these streams are compressed into. As far as the sound quality goes, you NEED to increase the volume a lot to get the same level of the audio in its original form. I think the sound is a little bit inferior to the Bitstream (direct) mode, especially the bass sounds a little mushy.
