On 10/15/2012 01:01 AM, Adriano Moura wrote: > 2012/10/14 Tanu Kaskinen <tanuk at iki.fi> >> I didn't get why 5.1 REAR should end up in 7.1 SIDE. If the content >> creator decided to put audio in a REAR channel, why shouldn't it be >> played to a REAR speaker? Is 5.1 content actually created with the >> assumption that in practice the so-called "rear" channels end up in >> "side" speakers? > > If you do a search for "5.1 speakers setup" you will notice that most > setups place the surround speakers at -90?/90? and nobody calls then > Rear or Back speakers, but Side or Surround speakers. If you mean Google image search, I find both 90, 110 and 135 angles. Wikipedia suggests 110, and the manual to my receiver suggests 120. I can't agree that 90 is the standard. And I also find several images referring to a "Rear" channel rather than "Surround" channel. > I don't know why > we call then REAR in a 5.1 arrange... maybe it's an Alsa thing that we > borrowed? They also list then as REAR. But anyway, 5.1 arrangement is > definitely meant to be played trough surround/side speakers. Most onboard sound cards that support 5.1 have 3 jacks: Green = front, Orange = center+lfe, Black = Rear/Back/surround. Those who support 7.1 have 4 jacks: Green = front, Orange = center+lfe, Black = Rear/Back/surround and Gray = Side. That looks to me as if the Side jack is the one extra, that should be silent (or extrapolated), when playing back 5.1 material on a 7.1 system. OTOH, referring to my receiver's manual, it defaults to upmixing the 5.1 surround channels to be played on both rear and side in a 7.1 speaker setup, but has the option of playing it only on the sides, rather than only on the rear. Maybe this is a case where there are conflicting de-facto standards? > 2012/10/14 Tanu Kaskinen <tanuk at iki.fi> >> I don't understand why openal would use PA_CHANNEL_MAP_WAVEEX to define >> its channel map, though. When openal creates a stream in pulseaudio, I >> would expect it to know exactly the channel map, and if it doesn't match >> with the WAVEEX definition, then it should use some other definition (or >> initialize the pa_channel_map struct manually). >> >> That said, if the mapping that you suggest for WAVEEX isn't any less >> conformant than the current mapping, this sounds like a useful change to >> make. Potentially it can break other applications that assume that the >> mapping is what it is now, but I find the existence of such applications >> quite unlikely... > > Again, I think they either didn't want to mess with > pa_channel_map_init or didn't realize WAVEEX was broken for 6.1 and > up... Well, few people have surround setups, even less so 6.1/7.1. (I > also don't, But I'm using binauralization with some nifty jack and > jconvolver DSP) Nevertheless, it sounds like this is something to be fixed in OpenAL rather than PulseAudio? Better specify the channel map explicitly. -- David Henningsson, Canonical Ltd. https://launchpad.net/~diwic
