MP3 or WAV: Which One Should You Actually Keep?
You've got a recording, and two choices for what to keep: MP3, which is small, or WAV, which is ten times the size for what sounds like the same audio. Deleting the "big" one feels like the obvious move, until you learn what each format is actually doing under the hood, and why that decision is hard to undo once it's made.
WAV stores the actual waveform
A WAV file is uncompressed PCM audio: the exact amplitude of the waveform, sampled thousands of times per second, written to disk with nothing removed and nothing approximated. That's the entire reason a WAV recording runs roughly ten times the size of an MP3 of the same audio, it isn't compressed at all. Every sample the microphone (or your audio software) captured is stored exactly as captured. There's no decoding step that has to "figure out" what the sound is supposed to be; the file just is the sound, as numbers.
MP3 throws data away on purpose
MP3 gets small through lossy psychoacoustic compression, meaning it deliberately discards information rather than just packing the same information more efficiently. Specifically, it identifies frequencies that are masked, drowned out by louder frequencies nearby that the human ear is statistically unlikely to notice, and removes them from the file entirely. At a reasonable bitrate the result sounds nearly identical to the original, because the missing pieces were chosen specifically for being pieces most people can't hear anyway. But the data is genuinely gone, not just hidden.
Converting MP3 back to WAV doesn't undo anything
This is the part that trips people up: converting an MP3 to WAV does not restore the discarded quality. The resulting WAV file gets bigger, because uncompressed storage is always bigger, but it contains exactly the same already-lossy audio the MP3 had, just re-encoded into an uncompressed container. There's no original data left anywhere to recover. Once those frequencies were thrown away during MP3 encoding, no later conversion, to WAV or any other format, brings them back. Think of it like re-photocopying a photocopy onto nicer paper: the paper improved, the image didn't.
The practical rule
Record and edit in WAV if you're doing actual production work. Uncompressed audio has no generational quality loss, so saving, re-opening, and re-saving a WAV file repeatedly during editing doesn't degrade it the way repeatedly re-saving a lossy format can. Once editing is finished and you're ready to distribute or share the result, convert to MP3. The size savings matter for distribution (uploading, emailing, streaming), and at that final listening stage the human ear generally can't tell the difference from the uncompressed original.
Converting
Convert WAV to MP3 when you're ready to share or distribute a finished recording, and convert MP3 to WAV if you need an uncompressed container for editing software that expects one, keeping in mind it won't add back any quality the MP3 already lost. Both run entirely in your browser.