Free Reverse Audio

Worked example

A 3:00 stereo song at 44.1 kHz. Drop it in and "Section to reverse" reads "3:00.00 of 3:00.00". Drag the "Start" and "End" sliders to 0:30 and 0:45 and it reads "0:15.00 of 3:00.00". "Play reversed" now plays just that section backwards, and nothing is encoded yet. Press "Reverse audio" with "Reversed section" selected to get a 0:15 clip. Choose "Original, then reversed" on the whole song instead and the page shows "Output length: 6:00.00". In a browser that can encode AAC, M4A is preselected for clips of 5 minutes or less; at 160 kbps the 3:00 song comes to about 3.4 MB. As WAV (16-bit, 44.1 kHz, stereo) the same 3 minutes is 30.3 MB, and the doubled 6:00 version is 60.6 MB. MP3 is written at 192 kbps, about 4.1 MB. When it finishes the page says "Reversed audio ready — 30.3 MB" for the WAV, and the download is named song_reversed.wav.

Which settings to use, and the limits

• Reverse just the part you want. The "Section to reverse" waveform has "Start" and "End" sliders. The two ends are kept at least 0.05 second apart, and the sliders move in steps of 0.1 second for clips of 50 seconds or longer and finer for shorter ones, down to 0.01 second. "Whole clip" appears next to the length once you narrow the section, and puts it back. Changing the section or the output mode clears any finished result and the preview, so the buttons never offer a file that no longer matches the settings.
• Pick what the file contains. "What to output" has three choices. "Reversed section" gives only the backwards audio. "Original, then reversed" and "Reversed, then original" give the section followed by its reverse, or the reverse followed by the section, joined back to back, so the file is twice as long; the page shows "Output length: ..." for those two. Every channel is reversed sample by sample, so a stereo recording stays stereo in WAV.
• Play it backwards before you save. "Play reversed" builds the reversed section in the page and shows a player with a seek bar; tick "Loop" to repeat it. "Hear it backwards right now — nothing is encoded until you press Reverse." The button appears once the page has read the file ("Reading audio…" shows while it works). It is not offered for clips too long for the quick path (see the limits below) or for files your browser cannot decode itself, which are reversed with the slower engine.
• Choose M4A, WAV or MP3 by what you need. "Output format" offers up to three buttons. M4A (shown only where the browser can encode AAC) is small and needs no download; it is the default for clips of 5 minutes or less, and it is written at 160 kbps. WAV is lossless, 16-bit and instant, but large: about 10.1 MB per minute for 44.1 kHz stereo. MP3 is written at 192 kbps and needs a one-time encoder download of about 30 MB. Your choice is kept while you change the section, and the buttons of formats you have already made show a tick.
• Record your own voice and hear it backwards. "Record and reverse" asks your browser for the microphone and records up to 2 minutes. "Stop and reverse" ends the take and plays it backwards at once; you can then pick a section, a format and download it like any other file. If the browser cannot record on this page, for example inside another app's built-in browser or on a page that is not https, a note appears in place of the button.
• Know the length limits. The file itself is refused above about 2 GB on a normal computer, about 1 GB on a computer reporting 4 GB of memory or less, and about 400 MB on a phone. What matters more is how much audio you reverse at once. Reversing needs the audio held in memory, estimated at 48 kHz stereo. Clips up to about 22 minutes on a computer, or 4 minutes on a phone, use the quick path with the instant preview. Longer clips are reversed with the slower media engine (about 30 MB to download) and have no preview, and a selection longer than about 69 minutes on a computer or about 18 minutes on a phone is refused. A longer file opens with the longest section that fits already selected. Videos (MP4, WebM, MOV) are accepted, but only the sound is reversed and saved as audio.

Common problems and how to fix them

It says "Microphone access was refused. Your browser will not ask again until you allow it in site settings."

This comes from "Record and reverse". After a refusal the browser does not ask again. Open the site settings from the address bar, set Microphone to Allow for this site, reload the page and try again. If you would rather not use the microphone, drop a recording file instead. Other microphone messages, such as "No microphone was found." or "The microphone is being used by another app or tab. Close it and try again.", mean there is no input device, or another app holds it.

It says "The selected part (about 80 min) is too long for this device to reverse. Select a section of up to 69 min."

Narrow the "Start" and "End" sliders to the stated length or less. "Reverse audio" is disabled while this shows. The limit is 69 minutes on a computer and 18 minutes on a phone, so on a phone it is much shorter. A long file normally opens with the longest allowed section already selected, so you see this message mainly after pressing "Whole clip". To reverse a longer recording, do it one section at a time.

It says "This is a long clip (about 1 min). The instant preview is off and it is reversed with the slower engine. Select a section of up to 22 min to keep it fast and safe on this device." and there is no "Play reversed" button.

Either the clip is longer than the quick path allows, or your browser could not decode the file by itself, which can happen with unusual formats whatever the length. Nothing is wrong. Press "Reverse audio" and the slower media engine does the work, about 30 MB to download the first time and with no preview. If you want the preview, save the audio as MP3 or WAV first, or select a section within the stated minutes.

It says "This browser could not create an M4A file. Choose WAV or MP3 instead."

The browser said it could encode AAC and then could not. The tool hides the M4A button and switches the format to WAV for you. Press "Reverse audio" again for a WAV, which is instant, or choose MP3 for a smaller file.

It says "The reversed audio could not be saved. Try again, or choose a shorter section."

The file could not be built in the page. Try again, and if it repeats select a shorter section with "Start" and "End", because the decoded audio, its reversed copy and the WAV file are all held in memory together while the file is made. WAV needs no encoder step. For MP3 and for long clips the page can instead show an engine message such as "The browser ran out of memory processing this file — it is too large for this device. Try a shorter clip, a smaller file, or a desktop computer."

How it compares

The reversal itself is exact: each sample is simply read backwards, so a WAV is the original audio reversed with no change in sample rate or channel count, and the M4A and MP3 are lossy copies of that. The "Original, then reversed" modes join the two parts end to end with no crossfade, so a click is possible at the join if the section does not start and end quietly. Compared with a desktop audio editor's Reverse effect, this tool reverses one section of one file at a time, with no timeline, no fades and no other effects. The quick path and the slower media-engine path give the same reversed audio, but the engine path has no preview and needs a download. In exchange there is nothing to install, and you can record and reverse your own voice in one step.