[LAD] Mixing audio: Implementing pan and balance

Geoff Beasley geoff at laughingboyrecords.com
Tue Mar 12 09:41:01 UTC 2013

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 :)

you're on the right track fior sure Tim



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