Convert Mono to Stereo Online

Duplicating is the safe one: both channels become identical, the file is a two-channel file, and it sounds exactly like the mono it came from. Take it when something downstream simply refuses a one-channel file. Pseudo-stereo is the effect: a slight delay and a touch of reverb on one side make a single voice feel wider than the middle of the head. It changes the sound, so it belongs on music and atmosphere rather than on a recording somebody has to trust.

No. Duplicate copies the same mono signal to both channels — it sounds identical. The purpose is to create a stereo file format that is compatible with editors and platforms that require 2-channel input.

Pseudo-stereo adds a slight delay and echo to one channel, creating a perception of width and space. It makes mono recordings sound less "flat" when listening on headphones or stereo speakers.

This is useful when building a stereo mix from multiple mono sources. You can pan different instruments to different positions in the stereo field, then merge them in an audio editor.

No, and it is worth being plain about it: a mono file never contained one. Two microphones in a room capture arrival-time and level differences that place each source between your ears; a mono recording threw all of that away before it was saved, and no processing brings back information that was never written. What you get here is width — a convincing impression of space, added on top. For anything where the position of a sound matters as evidence, the mono file is the honest one.