Two problems that arrive together: the file is in the wrong format, and only part of it is wanted. Drop a WAV or MP3, drag the piece you want out of the waveform, and save it as MP3 or WAV. Nothing is uploaded.
Trimming audio in a browser used to mean uploading it to someone. It does not any more: the decoder a browser plays a file with is available to the page, and it hands back the raw samples. From there a cut is arithmetic — copy a range, ramp the first and last few milliseconds so the join does not click, write a new header in front. The waveform is drawn from those same samples, so the silence at the start of a recording is something you can see rather than hunt for.
MP3 is the one part that is not free. No browser will encode one, so this page uses LAME compiled to JavaScript, fetched the first time you actually ask for an MP3 and never on page load. A WAV is a 44-byte header in front of the samples, which is why every editor accepts it and why it is the largest: a minute of stereo WAV is about 10 MB against roughly 1.4 MB at 192 kbps.
No, and there is nowhere for it to go: this site has no server that accepts files. The browser decodes the audio with the same engine it uses to play it, the waveform is drawn on a canvas from those samples, the cut is a copy of a range of them, and even the MP3 is encoded on your own machine. If you want to prove it, open the network panel while you work, or disconnect from the internet once the page has loaded — everything still works.
Because no browser will encode an MP3 for you. It will happily decode one, and it ships an Opus encoder, but MP3 encoding is not part of any web API — so this page carries LAME, the reference encoder, compiled to JavaScript. It is roughly 170 kB, and it is fetched the first time you press Cut & convert with MP3 selected: never on page load, and never at all if you only ever export WAV. A WAV, by contrast, is free to produce — a 44-byte header in front of the samples the decoder already handed over.
For music, 192 kbps is the point where most people stop hearing a difference, and it is the default here for that reason. Speech and podcast material are fine at 128 or even 96, because there is far less going on to encode. 256 and 320 are worth it only when the file is going into an editor and will be processed again. The size follows directly from the number: a minute at 192 kbps is about 1.4 MB, the same minute as stereo WAV is about 10 MB, and the estimate beside the button does that arithmetic for whatever you have selected.
Yes, a little. MP3 is lossy, so the file you loaded has already had information discarded; decoding it and encoding it again discards more, and no bitrate recovers what was thrown away the first time. It is called generation loss, and it is rarely audible after one round, which is why trimming an MP3 here is perfectly reasonable. Two habits make it a non-issue: cut from the original WAV when you still have one, and choose WAV as the output if the clip is going into an editor for further work.
Not quite, and no MP3 can be. The format works in frames of 1,152 samples, so every file is a whole number of frames long, and every encoder adds a short delay at the front that the decoder is meant to know to skip. A one-second selection therefore plays back as roughly 1.03 seconds, with a few milliseconds of silence at each end. For a clip, a ringtone or a sound effect that is invisible; for a loop that has to join to itself it is not. WAV has neither problem — a one-second WAV here is one second to the sample — so pick WAV for anything that will be looped or lined up against something else.
That is the browser rather than the tool. Web Audio decodes everything into a single context that runs at one rate — usually 44,100 or 48,000 Hz, whichever your sound device uses — so a file recorded at a different rate is resampled on the way in, and the number shown is the rate the samples now have. The conversion is high quality and inaudible; the practical consequence is only that a WAV saved here may be a slightly different size from the one you loaded.
Raise the fade for that end. Audio is a waveform, and a cut placed where the wave is halfway through a cycle starts the file at that value — an instantaneous step away from silence, which is heard as a click. Five milliseconds of ramp removes it and is far too short to be perceived as a fade; anything percussive can take 20 or 30 ms without losing its attack. Set both to 0 only when you want the samples exactly as they were, for instance when the piece will be joined to another.
Drop the loop, leave the start where it is, and press the 1s chip — the selection becomes exactly one second from the start point. Drag the left edge first if the first beat is not quite at zero, then press Cut & convert. If the clip will be looped again, choose WAV and set both fades to 0: the cut is then sample-exact and joins to itself, which an MP3 cannot do. If it will simply be played, MP3 with the default five-millisecond fades is the smaller file.