Audio reverser
Drop in a sound file, wait for processing, then press Play backward to hear the result. Download the reversed sound as a WAV file.
Drag an audio file in, paste, or click to choose
A whole folder works too · Ctrl/Cmd+V pastes · on phone this opens your file picker · up to 60 MB per file
How the reversal is actually done
The browser's own Web Audio API decodes the file you drop in — MP3, WAV and OGG all go through the same decodeAudioData() call, which is the same decoder a native <audio> tag would use, so it recognises whatever your browser can already play. Decoding produces an AudioBuffer: one array of sample values per channel, each value a number between -1 and 1 describing the speaker position at that instant, tens of thousands of them per second. Reversing the sound is exactly reversing that array — the sample that was last is now first, the sample that was first is now last, done independently for the left and right channels so a stereo file does not collapse into mono. Those reversed samples are then written into a WAV container by hand: a 44-byte header describing the sample rate and channel count, followed by the samples themselves interleaved and quantized to 16-bit integers. No audio library is involved in either step; both are small enough to write directly.
What this audio reverser cannot do
- The download is always a WAV file, whatever format you uploaded. Writing a compressed MP3 would need a separate encoder library, and WAV needs none — it is the format that comes for free once you already have decoded samples, at the cost of a larger file than the MP3 you started with.
- Input files can be up to 60 MiB. Decoding and WAV export use browser memory, so large or long recordings can take time or exceed the device’s available resources. Processing time depends on the file and device.
- Any effects baked into the original recording — an echo, a fade, a filter sweep — play backwards along with the audio, because this reverses the finished waveform rather than re-synthesising the sound from its components. There is no way to reverse the audio while leaving a specific effect forward-facing.
- A file your browser cannot decode at all (an unusual codec, a corrupted file, DRM-protected audio) is reported as unreadable rather than producing a silent or broken output.
Questions about reversing audio
Does reversing audio always sound backwards, or does it sometimes come out normal?
It always plays back in reverse order — that part is mechanical and exact. What varies is how recognisable the reversal sounds: a short percussive hit tends to become a distinctive swelling sound, spoken words become unintelligible syllables, and this is exactly the effect studios use for a reversed cymbal swell or an intentionally unsettling vocal.
Is any audio quality lost in the process?
The browser may resample audio while decoding it, and export converts the decoded floating-point samples to 16-bit PCM. Reversing only changes sample order, but the complete conversion is not guaranteed to preserve the source bit for bit.
Why is the output a WAV file instead of MP3?
The download format is 16-bit PCM WAV. It stores uncompressed audio, so the result can be much larger than an MP3 source. This tool does not offer MP3 export.
Is the audio file uploaded to a server?
No. Decoding, reversing and re-encoding all happen through the Web Audio API running in this browser tab. The file is read locally and never transmitted anywhere.
What audio formats can I drop in?
Whatever your browser's built-in decoder supports, which in practice covers MP3, WAV, OGG/Vorbis, and AAC/M4A in most modern browsers. If a file fails to decode, the page reports that clearly rather than producing a blank result.
