What reversing audio actually involves
Digital audio is a long list of numbers — amplitude measurements taken tens of thousands of times a second. Reversing a track means reading that list back to front, which is conceptually the simplest operation in this entire toolkit and, done on decoded samples, completely lossless.
The file is decoded into raw sample data, each channel is flipped independently so stereo imaging survives intact, and the result is written out as a WAV. Nothing is approximated, and reversing a track twice returns you to something bit-identical to the decode you started from.
Why the output is a WAV
This is a deliberate choice rather than a limitation. MP3, AAC and OGG are lossy: they achieve their size by discarding audio information permanently, and every re-encode discards more. Handing back an MP3 here would mean your reversed track had been through two rounds of that rather than one.
WAV stores the samples exactly as they came out of the reverse. The cost is size — roughly 10MB per minute of stereo audio, so expect a three-minute song to land near 30MB. If you want a compressed file, run the WAV through the Audio Converter afterwards, which puts the decision about when to lose quality in your hands rather than making it silently.
The resampling caveat
The Web Audio API decodes at the audio context's sample rate, which follows your output device and is usually 48,000 Hz. A 44,100 Hz source — which is to say, essentially every CD-derived track and most MP3s — is therefore resampled during decoding, before the reverse ever sees it.
There is no way around this in the browser: the API offers no option to decode at the file's native rate. In practice a single high-quality resample is inaudible, but it is a real transformation and the tool reports the rate it actually got rather than pretending otherwise.
The FFmpeg-based Audio Converter does not have this limitation, because it decodes and encodes without ever handing samples to an audio context.
Common uses
- Checking a track for backmasking — hidden audio meant to be heard in reverse
- Building reversed cymbals and risers for music production
- Making a reverse-reverb swell by reversing, adding reverb, and reversing back
- Creating sound effects for video and games
- Puzzle and escape-room audio clues