Finding your middle C

Interesting. I wonder if it makes volume adjustments more difficult as the preview is fading out in your ear and fading up on the external speaker?  I've considered a more mechanical approach, using a foot switch to toggle a preview signal on and off.  I don't like having a corded earbud in when I play though. Maybe a wireless earbud would be ok... Haven't tried one yet.

I have never tried Roger Ballenger’s inverse volume preview, but I’m not sure it is a good idea. It seems to me that if you are going to use an audio preview at all, it would be best to use one that is constantly at the same volume level (which could be adjusted to the needs of the moment) so you could train yourself to ignore it when you don’t want it.

If your preview volume level is dancing up and down all over the place and shifting every time you move your volume hand, it could be confusing. With a fixed volume level, you would know exactly where your preview sound is, and you could learn to hear past it. With an audio preview, it is essential that you teach your ear to distinguish clearly between preview and main volume output. The trick is never to have your preview any louder than it has to be for your particular audio environment. If you are playing in a noisy club, or with a large symphony orchestra, your preview will have to be much louder than if you were playing in your living room on a quiet Sunday afternoon.

That has been my experience.