Drop in almost any audio file and get a 48 kHz WAV back — the rate video and broadcast run at. No signup, no watermark, no limit on how many.
48 kHz means 48,000 samples of the waveform every second. It is the rate professional digital video settled on decades ago and never left: cameras record it, editing timelines default to it, DVD and Blu-ray carry it, and most broadcast and film delivery specifications name it outright. If a file is going anywhere near picture, this is the rate it is expected in.
Use it when audio has to sit on a video timeline — a voiceover recorded at 44.1 kHz, music licensed as a 44.1 kHz MP3, a sound effect library that predates your project. Use it when a delivery spec says 48 kHz and you would rather hand over a file that already is than argue about it. And use it when a project has files at two different rates and you want them all the same before you start editing, which is the version of this problem that costs the least to fix early.
The reason this matters is what happens when the two rates meet and nobody resamples. A 44.1 kHz file played as if it were 48 kHz runs 8.84% fast: an hour of audio finishes 4 minutes and 52 seconds early, and everything sits about a semitone and a half sharp. Modern editors resample for you and you never see it. Older tools, some hardware players and a fair number of automated pipelines do not, and the symptom — dialogue slowly sliding ahead of the picture, voices sounding oddly bright — is easy to blame on something else.
What resampling to 48 kHz does not do is add quality. A 44.1 kHz recording contains nothing above 22.05 kHz, and converting it to 48 kHz does not put anything there; you get a bigger file carrying the same music, with the samples interpolated onto a new grid. That is a perfectly good reason to do it — a consistent timeline is worth real time — but it is a compatibility fix, not an upgrade, and anyone selling it as one is wrong.
You get a WAV at 48 kHz. That is deliberate: this page changes one thing, and encoding the result into MP3 or AAC on the way out would stack a lossy re-encode onto a conversion you asked for for timeline reasons. A WAV drops straight into any editor, and if you need it as something smaller afterwards, the format converter will do that as a separate, visible step.
They come from different histories. 44.1 kHz was chosen so early digital masters could be stored on video tape; 48 kHz was chosen for professional digital video and audio equipment, where it divides cleanly against common frame rates. Neither is better — they are two standards that have both been entrenched for forty years.
No. There is nothing above 22.05 kHz in a 44.1 kHz file, and resampling cannot invent it. Do it for compatibility with a timeline or a delivery spec, not for quality.
It is, if the drift is a fixed proportion — an hour of audio ending about five minutes early is the 44.1-played-as-48 signature. If instead the drift creeps in slowly and unevenly over a long recording, that is clock drift between two devices, and resampling will not fix it.
A WAV at 48 kHz. At 16-bit stereo that is about 11.5 MB a minute, so a four-minute track is around 46 MB. Convert it to something smaller afterwards if you need to.
Any of MP3, WAV, FLAC, OGG, AAC, M4A, WMA, Opus and AIFF, up to 200 MB per file.