Open source: anyone can use, study and modify it, including businesses. Free: no cost, but the code is closed. Freemium: a lasting free plan with paid tiers for extra features. Source available: code is public but the license adds conditions.
FAQ
What is the best free alternative to Audition?
The most popular picks are Audacity, ocenaudio and Ardour. For voice recording, noise removal and podcasts: Audacity. For studio-style multi-track mixing: Ardour.
How do I remove background noise in Audacity?
Select a section that contains only noise, go to Effect > Noise Removal > Get Noise Profile, then select the whole track and run Noise Removal again at a moderate level (12 dB).