How to split a long audio file into separate parts
A two-hour recording is hard to navigate and hard to share. Split into blocks, it becomes a set of files you can name, send and find again.
Before you start: decide how to divide it
Spend a minute choosing the rule you'll use to split, because it decides every cut that follows. The common ones are:
- By topic or chapter. Best for classes, interviews and audiobooks. Each file has a meaning, but the lengths vary.
- By fixed length. Best for very long recordings you'll review later, such as meetings or field recordings. Ten or fifteen minutes per file is a good size.
- By speaker or song. Best for panels, live sets and rehearsals.
If you split by topic, skim the recording once at double speed in your usual player and write down the approximate times. It takes less time than hunting for each boundary inside the editor.
Step by step in Mp3Blocks
- Open the file. Drag it onto the box on the cutter page. The waveform shows where the speech or music is, and silent gaps look like thin flat lines, which are natural cut points.
- Name the series first. In “Next file name”, type the pattern you want with a two-digit number, for example
lecture-week3_01.mp3. The zero matters: without it, file 10 sorts before file 2 in most file managers. - Choose a folder (Chrome or Edge). Click “Choose output folder” once. Every block is then written there without a save dialog.
- Mark the first block. Drag from the start to roughly where the first part ends. Then type the exact end time if you noted one, or play the end of the block and press O at the moment you want it to stop.
- Check the edges. Press Space to play only the block. Use “Last 3 s” to hear how it ends. If a word is cut off, nudge the end a little to the right.
- Save. Click “Save selection”. The block turns green on the waveform, the list below shows its exact times, and Mp3Blocks selects the next stretch of the same length and changes the name to
_02. - Repeat. Adjust the new block's end, check it, save. Continue until you reach the end of the recording.
Made a mistake? Click “Select again” in the saved list to reload that block's exact range, adjust it, and save it with the same name to replace it.
Where to place the cuts
A cut in the middle of a word or a note is what makes split audio sound amateurish. A few habits avoid it:
- Cut inside pauses. Zoom your attention to the flat parts of the waveform between phrases and put the edge in the middle of the gap, not right after the last syllable.
- Overlap rather than lose. For speech, it is better to repeat half a second at the start of the next file than to lose the first word.
- Add a tiny fade. Set “Fade in” and “Fade out” to 0.05 s. It is too short to hear as a fade but removes the small click that appears when a waveform is cut at a non-zero point.
- Use longer fades only for music. One to three seconds suits songs and ambient recordings, but it will swallow words in speech.
Choosing the quality for every part
When you open an MP3, Mp3Blocks detects its bitrate and preselects the same value. Keep it: every file in the series should have the same quality, and going higher only makes files bigger. For voice-only recordings you are about to share by messaging apps, 96 or 128 kbps keeps files small with clear speech. The MP3 bitrate guide explains the trade-offs in detail.
After splitting
- Play the first few seconds of a couple of files to confirm the order and the start points.
- If the parts will be uploaded as a podcast or course, add the episode or lesson title to the file name, for example
03-pricing-strategy.mp3. - Keep the original recording. Each export re-encodes the audio, so it is always better to cut again from the original than from a part.