MP3, WAV and OGG — converted in your browser
Audio files fall into two broad groups. Lossless containers such as WAV keep every sample exactly as it was recorded, which makes them ideal for editing, archiving and mastering — at the cost of size, since a few minutes of CD-quality stereo runs into tens of megabytes. Lossy formats like MP3 and Ogg throw away detail the ear is least likely to notice, and in exchange a whole album fits in the space a single uncompressed track would take.
Bitrate is the main quality dial on a lossy file: it sets how many kilobits each second of audio is allowed to use. Around 128 kbps has long been the everyday standard for MP3, 192–256 kbps is the comfortable range for music you care about, and 320 kbps is the practical ceiling. Speech and podcasts survive far lower settings, and modern codecs such as Opus — the codec inside most Ogg files today — sound noticeably better than MP3 at the same bitrate, especially below 128 kbps.
Channels and sample rate matter just as much as bitrate. Collapsing stereo to mono halves the data a codec has to describe and is the right choice for voice recordings, interviews and phone-quality material. Sample rate sets the highest frequency that can be stored at all: 44 100 Hz is the CD standard, 48 000 Hz is the norm for video work, and dropping to 16 000 or 8 000 Hz shrinks a file dramatically while keeping speech perfectly intelligible. Converting between formats is always a one-way street — re-encoding something already lossy can never restore what the first encoder discarded, so always convert from the highest-quality source you have.