[LAD] Mixing audio: Implementing pan and balance

[Tim E. Real]

On March 12, 2013 03:08:18 PM Tim E. Real wrote:
> On March 12, 2013 08:41:01 PM you wrote:
> > On 03/12/2013 04:23 PM, Tim E. Real wrote:
> > > Hi, I need some advice, clear up some confusion:
> > > 
> > > I noticed our app uses this pan formula:
> > > 	vol_L = volume * (1.0 - pan);
> > > 	vol_R = volume * (1.0 + pan);
> > > 	
> > >   where volume is the fader value, pan is the pan knob value
> > >   which ranges between -1.0 and 1.0, and vol_L and vol_R are the
> > >   factors to be applied to the data when sending a mono signal
> > >   to a stereo bus.
> > > 
> > > When pan is center, 100% of the signal is sent to L and R.
> > > At pan extremities, the signal is boosted by 3dB.
> > > 
> > > But according to [1], we should be using a Pan Law [2],
> > > 
> > >   where pan center is around 3dB to 6dB down and pan
> > >   extremities is full signal.
> > > 
> > > So I want to change how we mix mono -> stereo and use
> > > 
> > >   true Pan Law. I could add a Pan Law selector, seems like it
> > >   might be useful for various studio acoustics.
> > > 
> > > Then I noticed we use the same formula above to apply 'balance'
> > > 
> > >   (using the same pan knob) when sending a stereo signal to
> > >   a stereo bus.
> > > 
> > > But according to [3] we should be using a true balance control, not
> > > those
> > > 
> > >   same pan factors above. And according to [1]:
> > > "Note that mixers which have stereo input channels controlled by a
> > > single
> > > 
> > >   pan pot are in fact using the balance control architecture in those
> > >   channels, not pan control."
> > > 
> > > So I want to change how we mix stereo -> stereo and use true balance.
> > > 
> > > But then I checked some other apps to see what they do.
> > > In an unofficial test I noticed that QTractor seems to do the same
> > > thing,
> > > 
> > >   that is, when pan is adjusted on a stereo track, one meter goes up
> > >   while
> > >   the other goes down. RG seems not to have stereo meters and Ardour
> > >   I couldn't seem to make pan affect the meters, I will try some more.
> > > 
> > > My questions:
> > > 
> > > Is the pan formula above popular?
> > > 
> > > What is the consensus on stereo balance - use a Pan Law, being the
> > > 
> > >   formula above or otherwise, or use a true balance?
> > > 
> > > What should I do in the remaining case sending a stereo signal to a mono
> > > bus? If I am using a Pan Law as balance, the two signals will have
> > > already been>
> > > 
> > >   attenuated at pan center so I could simply sum the two channels
> > >   together.
> > > 
> > > But if instead I use true balance, at center the two signals are 100%.
> > > So should I attenuate the signals before summing them to a mono bus?
> > > Currently as our pan formula above shows, there would be no attenuation.
> > 
> > you are right - it should attenuate in the middle and gain increase as
> > you move. i hate balance controls because you can't move the image
> > around the panorama. if you have a stereo piano sample for example, you
> > need to move all the "sample data" around the sound stage - not hear an
> > amplified L channel and an attenuated R channel which is the balance
> > model. Balance is for home stereo's. Pan is for grown ups :)
> 
> OK just to be clear I was not implying that the given pan formula
>  would be used to do a true 'stereo pan', just that the formula would be
> used to adjust stereo 'balance' giving almost the same results as a true
> stereo balance, but slightly different levels, but not a true 'stereo pan'.
> 
> But having said that, yes I'm wondering about a true 'stereo pan' feature.
> How would such a feature work?
> I imagine that if for example if there is sound exclusively on the L
> channel, and 'stereo pan' is at center then moved all the way to the right,
> the sound that was exclusively on the L channel now moves to the exact
> center? That is, all the sound in the stereo field now moves 90 degrees to
> the right? It means you'd never be able to completely move an exclusive
> sound which was strictly on L, all the way to the right.

Ah, the answer might be an 'expanded' pan range of -180 to +180 degrees
 instead of the normal -90 to +90.
That way something all the way on L could be moved all the way to R.
Right?
Tim.

> 
> Does that sound correct Geoff?
> I can easily implement a true 'stereo pan', given some rules.
> Just, now I'd have to give the user the option of using either pan or
> balance, complicating things a wee bit more, but probably nothing an
> additional small pushbutton or two couldn't fix.
> 
> Thanks.
> Tim.