100% correct.

You can rewrite the first sentence in a couple of different ways. For example: 1. Turn the music down; if not, you will wake up the baby. 2. Turn the music down because you'll wake up the baby. 3. Turn the music down, otherwise you'll wake up the baby. The second sentence is fine, except I would add a few words to the sentence if you want to use the word "low." 1. They speak AT A LOW VOLUME so they won't wake up the baby. 2. They speak IN A LOW VOICE so they won't wake up the baby. I hope this helps you! Let me know if I can help you with anything else.

Thank you

The first sentence works to get the point across, but could be said more fluidly as "If you don't turn the music down you will wake up the baby." In the second sentence "low" should be changed to an adverb, such as "quietly" but otherwise is good.