Combine Multiple MP3 Files into One Without Quality Loss with the Free Audacity

Step 1 — Open a NEW empty project

    File → New

Step 2 — Import All Files Together

    File → Import → Audio

They will appear as multiple tracks stacked vertically.

Select ALL MP3 files at once. (Ctrl + A)

Step 3 — Align Them Properly 

    Go To: Tracks → Align Tracks → Align End to End

Step 4 — Merge Into One Track

    Go To: Tracks → Mix → Mix and Render

This combines them into ONE continuous track. You should now see a single waveform.

Press play, and you should hear clean sequential audio.