Are the fades linear or curved?

Linear gain ramps via GainNode.linearRampToValueAtTime. That is the cleanest default for speech and most music.

Can fade-in and fade-out overlap?

No — the tool caps each fade so the combined length never exceeds the total duration.

No. Gain scaling is lossless; the only quality change comes from the final MP3 encode if you pick that format.

Add smooth fade-in and fade-out effects to your audio files.

Drop an MP3 or WAV file here

or click to browse

Your audio never leaves your browser. All processing happens locally.