Tried a search but didn't really find what I was looking for. Will show my total ignorance of surround modes and how they work, but here goes.

I have a 970/1075 setup with both my DVD and Cable/DVR outputting their audio via optical. I just don't get the surround modes, what the display shows, and why they sometimes change.

For example, for most television, trial and error determined that Dolby PLII-C sounds best. However, for some television the 970 reverts automatically to Dolby Digital, showing Dolby Digital and .0 or 2.0 or 3/2.1. Most of the time this is great as the sound is much improved, however, sometimes the switch will leave nothing on the center channel and a rather "flat" sound, so I manually switch it back to Dolby PLII-C. The manual is lacking in explaining this. I guess my questions are:

1. Is it autoswitching to a source that it recognizes, and if so, is it accurate?

2. What does .0, 2.0, and 3/2.1 indicate (2.0 and 3/2.1 I assume are 2.0 and 5.1 sources)? and what do they mean, the source, or the output?

3. Is it a typo that Dolby PLII-M, listed as Dolby Pro Logic II Movie, says Optimized for Music in the manual?

4. Despite the fact that I have the 970 set for no back surrounds, it still offers PLIIx as an option, is this right?

Any help with this is greatly appreciated, be it in directing me to the answer, or answering in as much detail as anyone is willing to spend the time to explain.

These are actually good questions, and solid fundamental information on how all of this works can be very difficult to track down. The 970 will automatically switch to the proper decoding mode when it detects a new source, and this switch is entirely accurate - it has to be for you to get any sound at all, since PCM stereo and the different flavors of Dolby Digital and DTS each must be handled differently to produce the intended audio. When the 970's display sees a new signal, it will briefly display the incoming signal's format: Dolby 2/0.0, for example, or PCM 48khz or Dolby 3/2.1.

When you see that "2/0.0" or other string of numbers, the 970 is telling you how many audio channels are present in a Dolby Digital or DTS bitstream. The first number (typically 2 or 3) relates to the front soundstage: 2 means stereo (left and right), while 3 means there is also a center channel as well. The second number (the one immediately after the "/") describes the surround channels: 2 means separate left and right surround signals, while a 0 means no surrounds and a 1 (which I wouldn't expect to see often) means a single mono surround channel that would be sent to both surround speakers. The last number (the 0 or 1 after the ".") refers to the LFE channel that is meant for the subwoofer. A 0 means that there's no LFE track, while a 1 means that there is.

After a few seconds, the 970 will switch to showing the actual processing mode being used to generate the output, which will include both the signal decoding if it's appropriate (such as Dolby Digital or DTS) and any additional processing (such as Pro Logic IIx or DTS NEO:6). Some of the processing in the 970 works only for decoding a specific signal - that would be Dolby Digital and DTS. Other processing is used to derive additional audio channels that don't explicitly exist in the original signal, which is done using matrix decoding modes such as Pro Logic II and NEO:6.

Typically, Pro Logic II Movie is listed as PLII-C for "Cinema" to differentiate it from "Music." In cases (such as Outlaw's 990) where the mode is spelled out completely, it is often listed as "Movie" and "Music," so it does get confusing. Since the 970's display is similar to that used on the Model 950, I'd suspect that if you see PLII-M you're getting the music form of Pro Logic II.

If you only have a 5.1 speaker setup, you are likely to still see Pro Logic IIx listed - II and IIx are the same basic animal, with IIx just adding the ability to handle surround back channels.

I've got a fair bit of detail written about surround modes here and here (pardon the repetition between the two), which may also help answer some lingering questions.

Thanks for the quick response. I will read through your links this evening and see if I can make sense of it. May have some follow up questions.

You know where to find us.

Seem to have pretty much figured it out. Best setting for me with Cable/DVR seems to be defaulted to PLII-C with 970 automatically switching to Dolby Digital when it gets the signal (pretty much limited to HD channels).

Two channels have me perplexed however. Both Weather Channels (ie THE Weather Channel) are broadcasting a Dolby Digital signal sensed by the 970. However, it shows "Dolby Digital .0". What does that mean.

Thanks!!

They may very likely be broadcasting in mono, which should show up as 1/0.0 - but considering how rare Dolby mono is it's very possible that there's a quirk in the 970's code that doesn't show anything that's gone pretty much unnoticed.