- The sound field right after the decoding stage can be pictured as a 2-dimensional square with the listener at its center; this sound field can be further transformed spatially in several ways. The default setting is to leave the decoded field as it is, i.e., if a stereo track was downmixed from a discrete 5.1 track (e.g., from AC3 format) and is upmixed again with FreeSurround, it comes closest to the original source material when using the default settings. However, music that was not originally meant for surround playback can be spiced up quite a bit using these controls. The first option (Panorama) is to wrap the sound field around the listener in a circular manner. The slider allows to change the angle that the front soundstage takes up (i.e., the line between the front left and the front right corner of the sound field). Originally it is 90 degrees, but if it is set to, say, 270 degrees the front stage will be wrapped from behind the left ear along the front to behind the right ear of the listener. While the front stage is expanded, the side and rear sound field must correspondingly be compressed into the remaining space behind the listener. The second option (Dimension) allows to shift the sound field forward or backward without changing the shape. The third option (Depth) essentially scales the sound field to the back, i.e. the original square is resized along one axis (while the front stage stays where it is). These transforms are applied in the order in which they are listed here (the order matters). The last slider (Focus) is a bit experimental -- it allows to change the angular spread of the individual sound sources, either by making them more focal or less (i.e., more ambient). This is only really noticable with lots of speakers, but I would not overdo it.
- The second group of controls is how the sound field is mapped onto the speakers. The first setting here is the channel setup; this allows you to select how many speakers you have and where they are placed (front left and right, center, rear left and right, side speakers, etc.). From the point of view of the decoder there at 16 possible positions along the edges of the square sound field (see this picture for an example), namely the 4 corners, the 4 midpoints (front center, back center, left side, and right side), and two positions on each edge half-way between the corners and the midpoint (e.g., front left center, front right center). Most people have only a subset of all these channels (e.g., 7.1) in some common locations, but you can have some fairly arbitrary setups (***). But note that the placement of the speakers in the room is actually not in a rectangle but instead follows the corresponding home theater rules. If you have a subwoofer you might want to do the bass management right here, but it is usually a better idea to let the sound card or amplifier do it if they offer the option (e.g. for active sub-satellite systems). The last option in this box is the stereo separation; this allows to effectively stretch the sound field horizontally in the front and/or back areas.
Thanks. You can see from the part bolded that upmixing from original stereo is treated as a 'bonus' to FreeSurround's main function, which is: re-upmixing stereo downmixes of Dolby surround audio -- a function hardly useful to anyone anymore. This bemused me over and over while reading that thread. It's like saying oh, btw, at the end of this rainbow I've made, there's a pot of gold, you might want to check that out too. I don't know if that was sincere or just a ploy to deflect interest from Dolby Labs. Dolby very much marketed PL II's stereo-to-surround capability, over its Dolby decoding function.
The Dolby PL II emulation seems clear --
Panorama and
Dimension were user-adjustable parameters in DPL II Music mode.
Depth seems to be for expanding the rear soundstage -- not really sure. It's not something DPL II offered. Ditto the
Focus option.
I've already wondered at the absence of DPL II's
Center Width (in the version I downloaded at least). Not sure why it went missing. Default setting was '3' for PL II, IIRC.
Also not sure how 'stereo separation' option mention at the end, differs from Depth, at least in terms of the rear channels.
