Once your project is organized enough to manage, it's time to set your levels. Mixing means raising some levels and lowering others. Because of this, set your Mixer channels to unity gain (see sidebar, "Unity Gain"), or 100, before you start mixing.
If your song's volume is going to increase down the line, or you are using a lot of distortion effects in your tracks, you might even want to set your initial levels lower still, to about 7580.
This unused gain is sometimes referred to as headroom, and it is both a protection measure and a tool for you as you mix your music.
Headroom makes sudden sound spikes less likely to distort and leaves space to bring a solo instrument to the forefront when you want to.
To add headroom to a Mixer's settings
First set your Mixer's master faders to unity gain by Ctrl-clicking (Win)/Cmd-clicking (Mac) the fader.
This is especially important for chained Mixers, because the master outputs of a chained Mixer control the master levels for Mixers down the chain.
Choose how much headroom you think you need for your song, and set your Mixer's channel faders at unity gain or below it.
Use the same settings for all submixes and Mixer chains in your setup.
Reason's Mixers have a range from 0 to 127. When a fader is set at 100, it is said to be at unity gain, meaning it isn't boosting or lowering a signal level.
Use fader values below or at unity gain unless you need to alter a signal's level in some way. You will preserve your chosen amount of headroom, keep your mixing levels from varying too much, and make it so you only have to look at automated data when making an adjustment or fixing a level that's gotten too high.