Why most MP3 cutters make your file worse
An MP3 cutter has two ways to do the job. It can decode the whole file to samples, throw away the part you did not want, and encode what is left. Or it can find the frame boundaries either side of your selection and copy those bytes out.
Almost every one online does the first. That second encode is a second generation of loss, applied to audio you never asked to have re-processed, and it happens even when you are trimming one second of silence off the end of a three minute track. The frequencies the first encoder threw away are gone either way. The second pass then goes to work on what survived, and picks a slightly different set of things to discard.
This one does the second, whenever it can. It is not a better encoder, it is no encoder at all. The badge above the save button tells you which path you are on before you commit to it, and what it cost is measured over ten generations on the guide, on a file you can reproduce.
The one thing a frame copy cannot do
Land the cut exactly where you put it. An MP3 frame holds 1152 samples and cannot be split, so the in-point moves to the nearest frame boundary. At 44.1kHz that is a quantum of 26.122 milliseconds, and at 48kHz it is 24 milliseconds.
In practice that is under half the length of a spoken consonant, and well inside the gap between two words. It matters for exactly one job, which is cutting a loop that has to line up to a beat, and for that the answer is to save as WAV and accept the size. Everything else is better served by the copy.
The tool never rounds this quietly. The toast after you save says how far the cut actually landed from where you put it, in milliseconds, and it says nothing when the two agree.
Six ways to place the two points
| Way | Reach for it when |
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| Drag on the waveform | You can see where the section is. Dragging on empty waveform starts a new selection, dragging inside moves the one you have, and a double-click selects the whole file again. |
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| Type a time | You already know the numbers, from a transcript or a note. The fields take 1:23.500, 83.5 and 0:83 and all three mean the same thing. |
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| Press I and O | You are listening for the point rather than looking for it. Play it, and press the key at the moment it should start or stop. |
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| Nudge with the arrows | The point is nearly right. Ten milliseconds a press, a full second with Shift, and one millisecond with Alt held. |
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| Snap the length | The far end is fixed by whatever you are making. Thirty seconds for an iPhone ringtone, forty for Android, fifteen for a Reel. |
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| Set the length field | You know how long the clip has to be and where it starts. Typing into Length moves the end point and leaves the start alone. |
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Zoom, and why no other browser cutter has it
Every online cutter draws the whole file across one screen width. On a three minute track at 1200 pixels that makes one pixel worth 150 milliseconds, so the finest cut you can place by dragging is six times coarser than the frame quantum you are cutting on. The precision is there in the format and the interface throws it away.
Scroll on the waveform to zoom around the pointer, or use the slider. Past 1× an overview strip appears underneath showing where you are in the whole file and where the selection sits, because zooming without one is how people get lost. Drag on that strip to move the window. Press 0 to fit the file back on screen.
Fades, and what turning one on costs
A fade has to be multiplied into the samples, and samples only exist after a decode. So setting a fade above zero turns the lossless path off and the badge says so on the spot, naming the fade as the reason. The file then comes out as a WAV.
Both fades are equal-power rather than linear, which means the curve is a quarter sine instead of a straight line. A linear fade sounds like it dips in the middle, because loudness follows power and power follows the square of amplitude. It is the difference between a fade that sounds smooth and one that sounds like a hole.
If all you want is to stop a clip ending on a hard edge, try moving the out-point into a quiet moment first. That keeps the copy, and on most material it sounds better than a fade anyway.