Converting MP3 to WAV is about compatibility, not quality. Some audio editors, samplers, DJ software, CD burning tools, game engines and hardware devices want uncompressed PCM audio and will not load an MP3, or load it with a delay at the start that throws off timing. WAV removes those problems. This page opens with WAV selected as the output; drop the MP3 files and convert, and you get 16 bit, 44.1 kHz stereo WAV, the CD standard that every application opens. Two things are worth knowing before you do it. The file grows a lot, roughly ten times, so a 5 MB MP3 becomes a WAV of about 50 MB. And the sound does not improve: the detail the MP3 encoder discarded is gone for good, so the WAV is an exact, uncompressed copy of the MP3 as it sounds now. If you have a lossless original, convert from that instead. Some phone systems and announcement players need a different variant, such as 8 kHz mono, which this page does not produce. For editing, keep working in WAV until the final export to avoid adding another round of MP3 loss. To go back to a smaller file use WAV to MP3 Converter, and for Apple files see M4A to WAV Converter.
The split that matters most in audio formats is lossy against lossless. A lossless format such as WAV or FLAC stores enough information to reconstruct the original waveform exactly, which is why WAV files run around 10MB per minute of stereo CD quality audio. Lossy formats such as MP3, OGG Vorbis, AAC, and Opus use psychoacoustic models to discard sound that listeners are unlikely to perceive, typically hitting a tenth of the size for audio most people cannot distinguish in normal listening. The important consequence is that the discarded information is gone permanently. Converting MP3 to WAV inflates the file back to full size without recovering anything, and each further lossy conversion compounds the loss, an effect known as generation loss. The practical rule is to keep a lossless master and export lossy copies from it, rather than converting between lossy formats repeatedly. Bitrate is where quality and size are actually traded. At 128 kbps most listeners cannot reliably distinguish MP3 from the source on laptop speakers or earbuds, though the gap becomes audible on good headphones with dense music. At 256 to 320 kbps MP3 is effectively transparent for nearly everyone. OGG Vorbis reaches similar quality at a somewhat lower bitrate, because it is a newer design than MP3, and Opus does better still, which is why messaging apps and voice chat use it. Sample rate and bit depth apply to the uncompressed side. This tool writes WAV at 16 bit and 44.1 kHz, the CD standard, which is the format editing software and mastering workflows expect, and which every audio application on every platform can open without conversion.