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

[Richard Bromley]

Whenever I play Dolby Surround DVDs in MPlayer (with -af surround), I
always get results similar to yours. That is,

1. the surround channel sounds like a mix of the L, R, and C channels,
rather than a separate, discrete channel, and
2. the center channel doesn't decode at all, staying in the L and R channels.

I'm pretty sure this is not the correct behavior for a Dolby Surround decoder.

So, it doesn't sound like you have something wrong with your setup,
unless both of us do. This issue has bothered me for some time, in
particular because nobody on the dev team seems interested in
addressing it (I'm not a dev, so I don't know for sure).

On 7/1/06, Jason Ferrara <jason at discordia.org> wrote:
> 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
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