Convert MP3 to WAV

No — converting cannot restore detail the MP3 already discarded. What you get is a lossless WAV of the current audio, which editing tools handle better and which will not lose more quality on further edits.

Yes. It is decoded on your own device with WebCodecs and never uploaded, so there is no account, no quota and no server that sees your audio. WAV files are large, so very long recordings depend on your device’s memory.

Because a lot of audio software works best from uncompressed PCM. Editors, DAWs and samplers can load a WAV instantly, edit and scrub it without decoding, and process it without stacking another round of lossy compression. The WAV will not sound better than the MP3 — it cannot recover what MP3 discarded — but it is the clean, editable starting point those tools expect.

Considerably — often around ten times the MP3. WAV stores every sample uncompressed, so a few-megabyte MP3 becomes tens of megabytes, and long recordings run to hundreds. It is a working format, not one for storage or sharing: convert to WAV for the tool that needs it, keep the MP3 for everything else, and do not archive the WAV unless you have a reason to.

It follows what the MP3 decodes to — typically 44.1 kHz at a standard bit depth — without resampling to something else. The tool decodes the MP3 to PCM and writes those samples straight into the WAV, so the result matches the original rate. That keeps it predictable for the editor or pipeline you are feeding it into, which may care what rate it receives.