Why AIFF to MP3, for this AIFF file
An AIFF master is too big to email or to drop in a podcast host.
The MP3 sound you will actually get
The uncompressed file is encoded as MP3 on your device. Speech can be smaller than music.
Keep the AIFF. Every later MP3 save throws away a little more, and you cannot return to this AIFF from the MP3.
AIFF to MP3 without the extra promises
AIFF to MP3 sits on this site because AIFF and MP3 are not interchangeable, even when they look similar in a file list. An AIFF master is too big to email or to drop in a podcast host. Use AIFF when a Mac tool refused WAV or MP3 and named AIFF. Podcast hosts, cars, WhatsApp, and old speakers expect MP3.
The uncompressed file is encoded as MP3 on your device. Speech can be smaller than music.
Read this about AIFF before you upload
AIFF is Apple uncompressed audio, similar to WAV. Editors on a Mac expect it. AIFF made from MP3 becomes large and does not sound better.
Keep the AIFF if you will edit. Share MP3 only as a copy.
Read this about MP3 before you send the download
The download has to be MP3, because that is the format the next step named. Podcast hosts, cars, WhatsApp, and old speakers expect MP3. Compatibility is the reason to make an MP3, not an improvement in sound.
Convert once from the best master you have, at the end of the edit.
Keep, check, then delete
People lose time when they convert before they know which rule failed. Size, pixel dimensions, codec, font encoding, and layout are different rules. AIFF to MP3 only addresses the AIFF to MP3 step. An AIFF master is too big to email or to drop in a podcast host. The uncompressed file is encoded as MP3 on your device. Speech can be smaller than music. Keep the AIFF. Every later MP3 save throws away a little more, and you cannot return to this AIFF from the MP3. The file stays on your device. The first run downloads a converter, so keep this tab open. A phone runs out of memory on long files. A computer is the safer place for a big clip. Do the test with a short or simple file first when the real file is large. A one-page PDF, a single photo, or a one-minute clip will show you whether the output is the kind of file you needed. After that test looks right, run the real file once. Keep both the AIFF original and the MP3 download until the receiving person or the upload form accepts it. Audio conversions are one-way once the format is lossy. AIFF to MP3 can change the container or the codec so a player opens the file. It cannot make a muffled take clearer, and it cannot turn an MP3 into a studio master by calling the result WAV or FLAC. Finish the edit on the best copy you have, then make the share file once.
Here is the decision for AIFF to MP3. You start with AIFF and you stop when a real program accepts MP3. A real AIFF master is a fine archive on a Mac. Each MP3 save throws away a little more. Turning MP3 into WAV or FLAC does not bring the lost detail back. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Keep the AIFF. Every later MP3 save throws away a little more, and you cannot return to this AIFF from the MP3.
A related step, if you still need one, is MP3 to AIFF.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.