How the audio trimmer works
When you open a file, the tool decodes the sound in your browser and measures the loudest point in each of about 1,200 small slices. Those peaks draw the waveform: tall bars are loud, flat stretches are quiet. Silence at the start of a voice note or the gap before a chorus is easy to spot, so you can place the handles by eye and then fine-tune them by ear with Play selection.
When you click Trim audio, only the part between the handles is written to the new file. If you keep the same format and add no fades, the original compressed audio is copied without re-encoding, so there is no quality loss. Otherwise the clip is decoded, the fades are applied, and it is encoded as MP3, M4A, OGG or WAV. Nothing is uploaded at any point.
How fades work
A fade changes the volume gradually instead of starting or stopping abruptly. This tool uses a straight-line (linear) fade:
volume at time t = (clip length − t) ÷ fade-out length (during the fade-out)
So with a 2-second fade-in, the sound plays at 0% volume at the very start, 25% after 0.5 s, 50% after 1 s and full volume from 2 s. If the fades are longer than the clip allows, they are shortened so they never overlap past each other.
Worked example: a 30-second ringtone
You have a 3-minute MP3 song and want the chorus from 1:02.0 to 1:32.0 as a ringtone.
- Drag the handles to roughly 1:02 and 1:32, then type 1:02 and 1:32 in the Start and End boxes for exact times. The length shows 30 s.
- Set Fade in to 0.5 s so the ringtone does not start with a click, and Fade out to 2 s.
- Choose M4A for an iPhone or MP3 for Android, at 192 kbps.
- Size: 192,000 bits × 30 s ÷ 8 = 720,000 bytes, about 0.7 MB.
| Clip | Format | Size |
|---|---|---|
| 30 s | MP3 192 kbps | about 0.72 MB |
| 30 s | M4A 128 kbps | about 0.48 MB |
| 30 s | WAV 44.1 kHz stereo | about 5.3 MB |
| 5 min | MP3 128 kbps | about 4.8 MB |
Choosing the output format
- MP3: plays everywhere. The default when your original is MP3, FLAC or another format.
- M4A (AAC): better quality at the same size; native on iPhone, iPad and Mac.
- OGG (Opus): excellent quality at small sizes; good for the web and Android.
- WAV: uncompressed, for further editing in an audio program.
The tool starts with the same format as your file where it can, so a cut M4A stays M4A.
Tips and edge cases
- Cut on silence. Place the handles in quiet parts of the waveform to avoid chopping a word or note in half.
- Short fades for speech. 0.3–0.5 s smooths the edges of a podcast clip without cutting off words.
- Lossless MP3 cuts are accurate to one MP3 frame (about 26 milliseconds), which is too short to hear.
- Video files work too. Drop an MP4 and you get just the sound. To keep the picture, use Trim Video. To get the whole soundtrack of a video, use MP4 to MP3.
- Change format without cutting? The Audio Converter handles whole files in batches.
- Record something first with the Voice Recorder, then trim the silence at either end here.
- Long files take a little longer to draw, because the whole file is decoded to measure the waveform.