[MPlayer-users] surround filter doesn't seem to work correctly

[Jason Ferrara]

I was trying to use the surround filter to watch things with dolby  
surround audio, and while I was getting sound out of the surround  
speakers, things didn't sound right, so I did a test of the surround  
filter.

I have a DVD from Dolby that has channel check test audio for Dolby  
Surround, Dolby Pro Logic II, and Dolby Digital. I ran these test  
using mplayer to do the surround sound decoding, and using my  
receiver (Denon AVR-1601) to do the surround sound decoding.

To let the receiver do the surround sound decoding, I did "mplayer - 
ao alsa:device=spif dvd://" and have the spdif out on the sound card  
connected to the digital in port on the receiver.

To have mplayer do the surround decoding, I did "mplayer -ao  
alsa:device=surround51=2 -channels 6 -af surround  dvd://" and have  
all the analog outs on the sound card connected to the 6ch in ports  
on the receiver.

I don't have a subwoofer connected, so I didn't test the LFE channel

The tables below show the channel being played and which speakers the  
sound came out of. (LF=left front, C=center, RF=right front, LR=left  
rear, RR=right rear)
Dolby surround:
channel      receiver surround decode     mplayer surround decode
-------           ----------                   ----------
left              LF               	        LF, LR, RR (LR and RR  
slightly lower in volume)
center            C                             LF, RF
right             RF                            RF, LR, RR (LR and RR  
slightly lower in volume)
surround          LR, RR                        LF, RF, LR, RR

Dolby pro logic II:
channel      receiver surround decode     mplayer surround decode
-------           ----------                   ----------
left               LF                           LF, LR, RR (LR and RR  
slightly lower in volume)
center             C                            LF, RF
right              RF                           RF, LR, RR (LR and RR  
slightly lower in volume)
right surround     LR, RR (RR slightly louder)  LF, RF, LR, RR
left surround      LR, RR (LR slightly louder)  LF, RF, LR, RR

And to make sure I don't have the 6ch inputs connected wrong or  
something, here is the same test using the Dolby Digital test without  
the surround filter ("mplayer -ao alsa:device=spdif -ac hwac3 dvd://"  
for receiver decode, "mplayer -ao alsa:device=surround51=2 -channels  
6 dvd://" for mplayer decode)
Dolby digital
channel      receiver surround decode     mplayer surround decode
-------           ----------                   ----------
left               LF                           LF
center             C                            C
right              RF                           RF
right surround     RR                           RR
left surround      LR                           LR


So, is this how the surround filter is known to behave, or do I have  
something screwy in my setup somewhere?


Thanks

- J