Why are Google Talk notifications at a low volume? When I am chatting with someone in Google Talk and I receive a message, the notification sound is played at a very low volume, low enough that I have some difficulty hearing it.

But if I receive a message in Google Talk while the application isn't open, the notification sound is at full volume.

I have notification volume cranked up to maximum in Android's settings, and Google Talk doesn't seem to have a separate setting for this that I've been able to locate.

How do I get my notifications to be played at full volume in Google Talk?

The device is a Motorola DROID RAZR MAXX with Jelly Bean 4.1.2.
When you are chatting with someone, you already know that you are chatting. You can see messages as they come. You are already notified. 

So Google Talk behaves intelligently and reduces notification volume. - thats for your answer

To get louder notification, the only way to fix this would be a Custom ROM with modified Google Talk app, where you can disable this feature.