[Openal-devel] new panning algorithm

[Joss Sanglier]

On the panning - basically if you send a stereo signal to the front 
pair, the LR, then the C will contain any mono information from that 
sound (I think I may have mistyped about that somewhere)

The problem with that is that is does have some narrowing effect on the 
sound. Now, I have to say this is how it works in DOlby and THX. I am 
assuming it is the same in computer systems since it is described as 5:1.

Obviously, if the listener does not have a centre speaker (not the 
effects channel - the sub woofer), then there is not an issue. If they 
do, then there is.

In Dolby we get round this confusion with flags. The system understands 
that certain things are not required and switch them off depending on 
the playback set up. Computers definitely do not do that.

I think there is a major confusion. Surround is NOT quadraphonic. In 
Quad (which I used to use in the 70s) the signals between speakers was 
equal, and the panning between them was also equal. It was assumed that 
the 4 speakers would be matching and the listener would be in the centre.

With surround, it is assumed that the quality speakers are the LCR 
speakers and the surround speakers are support, and normally smaller and 
of lesser frequency range. Consequently, you mix to that formula. The 
reason for this is that the point of focus should always be infront of 
the listener, and the listener is always static to the screen. In quad 
it is often the case that the listener moves and turns in the space - 
for instance an installation - and so you want it balanced all round.

Now, this is the point that I get it all wrong as I am not up enough on 
game technology!

It seems to me that games treat the sound as Quadraphonic. However, the 
player (the listener) is listening on a surround system. This is 
awkward, to say the least and would also explain why a friend of mine 
keeps blowing out his rear speakers! hehe

We also have the problem that in the majority of home spaces the 
speakers are really badly set up (the players think they are wonderful, 
but trust me, they are not). So mixing for them is a real pain. With 
cinema both the studio and the theatre have to have a very expensive 
Dolby Licence, and Dolby come and tweak the set up to their standard. 
Thus, if it sounds good in the studio it sounds good in the theatre.

We almost need a test system for each game where the player is told to 
put a microphone where they sit, pointing straight up, then we run a 
little application to work out what the player is hearing and optimising 
the output of the specific sound engine.

Chris Robinson wrote:
> On Sunday 25 January 2009 12:04:44 pm Joss Sanglier wrote:
>   
>> I am resending this as looking at another post, this may not have gone
>> through a few days ago - sorry!
>>
>> Not sure if this is any help in working out what your final effect
>> should achieve:
>>
>> http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professio
>> nal/44_SuroundMixing.pdf
>>
>> This is the manual for one of the pro dolby studio units. It discusses
>> true speaker placement as well as use.
>>     
>
> It's an interesting read, regardless. Thanks. :)
>
>   
>> In theory, in a cinema, if everyone in the audience could sit in the
>> precise middle of the screen, then there would be no need for a centre
>> speaker, as the combined left and right pairing would give the correct
>> balance. However, sitting left or right means that the voice would be
>> imbalanced. So a centre channel is added to a dedicated speaker to fix
>> the voice to the centre of the screen.
>>
>> The down side of this is that because a stereo sound (music for
>> instance) also contains a lot of mono L+R information, this will also
>> use this channel and result in a narrowing of the stereo field.
>> Consequently, we often produced stereo tracks that were "wider" than
>> would be mixed for normal stereo to compensate, or occasionally add a
>> very small delay to the right channel (not good on music).
>>     
>
> So does that mean stereo sounds should mix into the center channel? Or is that 
> mainly for 5.1-mixed tracks? I ask because at least some in rendered music 
> (like MIDI-to-wave, or module formats, that are played in real-time), mixing 
> the left and right channels into the center would dull the perceived stereo 
> effect, causing notes that are panned left to become panned halfway between 
> center and left.
>
>   
>> The other problem with games, (and I think this is especially affecting
>> MMOs now) is panning through centre which is a little too fast. In real
>> life, though we may turn our head slightly from left to right when
>> talking to someone, we perceive the sound as still being in front of us
>> until we move our head to either the extreme left or right. This is
>> something that the brain sorts out for us in some way. However, with the
>> artificial movement of sound created in a surround field in respect to
>> an avatar the brain does not have the same information as it would in a
>> real life situation and does not do this. In consequence the sound seems
>> to move very quickly from centre to left or right.
>>     
>
> I think this could be mostly resolved on the application side. For example, 
> keeping the listener orientation facing auditory points of interest (eg. 
> someone talking) even if the camera moves around a bit. Then reorient it when 
> you look far enough away.
>
>   
>> There is another problem in games which is the binaural or dummy-head
>> effect (or lack of it). Sounds behind your avatar should be duller than
>> the sounds ahead. There is an argument that says that since the two main
>> SS speakers are placed behind the listener then this real life
>> positioning should do the job. However, since it is common for the rear
>> speakers to be not directly behind but very nearly to the side of the
>> listener then I am not convinced this is happening appropriately. It
>> was actually easier with the older true dolby stereo (LCRS). With only
>> one mono surround channel (even if split over several speakers) the
>> sound was naturally duller. But with a true stereo pair, the sound is
>> normally as fresh sounding as the front speakers.
>>     
>
> I've thought about the idea of a listener cone before for a similar reason. 
> But I also somewhat dismissed it for the similar thought, "a real surround 
> sound setup would naturally dull the sound anyway". I don't think it would 
> actually be too difficult to add listener cones to OpenAL.. but it may not 
> interact well since as you say, you can't know the user's speaker setup 
> (enabling it for stereo may produce good results, but perhaps not as good for 
> surround sound setups).
>
>   
>> However, it would be interesting if a switch could be added to the
>> output of the mix that perhaps is called something like "enhanced
>> binaural positioning" where is reduces the bandwidth of the SS tracks
>> and changed the way the front panning worked. Something like that.
>>     
>
> Not sure changing the way panning works is a good idea, as a game designer can 
> have proper control over it and they would know best what to focus on. Though, 
> I probably could add a config option that applies the cone logic to the 
> listener->source position (similar to the logic there for
> source->listener) that's left for the user, not the app. It can modulate the 
> gain and high frequencies with the low-pass filter that's already being used.
>
>   
>> Anyway - it was the manual that was the important bit! Sorry!
>>     
>
> No need to apologize. You brought up some interesting points. :)
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>   

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