Convert AAC audio to an MP3 that plays on any device or player, right in your browser. Choose the bitrate and download — nothing is uploaded.
AAC is the codec inside M4A files and most streamed and purchased audio — technically a bit more efficient than MP3 at the same bitrate. A raw .aac (ADTS) file is that same codec without the MP4 wrapper, and it's exactly what some devices and editors won't touch. Converting AAC to MP3 swaps a marginally-better-but-fussier format for the one with the widest support of any audio format there is.
Both are lossy, so this is a transcode: pick 256 or 320 kbps so the extra encoding pass doesn't audibly soften the result, and always convert from the best AAC source you have rather than a chain of re-compressions. Everything runs in your browser with no upload. If your file is actually an .m4a, the dedicated M4A to MP3 page frames it that way; for other targets there's the full audio converter.
AAC is a newer codec that's slightly more efficient than MP3 — a bit more quality at the same bitrate — and it's what most streamed and purchased audio uses, usually inside an M4A container. A raw .aac (ADTS) file is that same codec without the wrapper. MP3 is older and marginally less efficient, but it has the widest device and software support of any audio format, which is exactly why you'd convert to it.
It's a lossy-to-lossy transcode, so there's some loss, but it's minor if you keep the MP3 bitrate high — 256 or 320 kbps. The bigger risk is compounding: converting an already low-bitrate AAC to a low-bitrate MP3 stacks two rounds of compression audibly. Convert from the best AAC source you have, at a high MP3 bitrate, and the result holds up well.
Almost — an .m4a file is AAC audio inside an MP4 container, while a .aac file is the raw AAC stream. Both convert to MP3 the same way here. If your file is specifically an .m4a, the dedicated M4A to MP3 page frames it that way, but this page will convert it too. Either way it's decoded and re-encoded entirely in your browser, with nothing uploaded.