I read somewhere that before mastering we have to do this in our mix. "Leave enough headroom in your mix, we recommend a maximal peak amplitude of -3 dBFS." But I don't understand. What is headroom, and what does -3dBFS means, and how to do this in Caustic. Please somebody explain.
What does this mean and how can I achieve it in Caustic?
Basically don't have your mix clipping, keep the bouncy lights in the master section in green, certainly don't let it clip. Then when you export for mastering there's plenty of volume spare to deal with compression and boosting shiz without any distortion going on.
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Caustic doesn't have any numerical indicators but the basic idea is what Rob just told you. Watch the master level indicators through the track and make sure you aren't hitting red. Probably best to stay out of yellow, except for brief spikes.
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Before exporting the song as "wav", you can lower the output volume, so that the red light does no occur in the master level indicator. For instance, use one of the limiter faders for a "master gain", then you can use the main fader for "fade in" and "fade out" automation.
Personally I would avoid compression or limiter in the master section and just let the mastering software handle that, the limiter in the master section is not nearly as good as the limiter in the mastering app likewise with compression. Just keep the output volume in the green as much as possible and let the mastering software boost the volume
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To my opinion the built-in limiter has a much too high threshold. But it can be used to trim the level of the whole mix (without reduction of dynamics) like an additional master fader.