eMastered is completely free to test and hear how the engine can improve your audio files. You are only asked to pay if you wish to download an eMastered mastered version of a song you upload.

To test it out all you need to do is click on the pink upload circle on the center of the website, and select the song you wish to have mastered.
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From there the engine will master your song, and you'll be able to preview it and compare it to your unmastered version free of charge.