Why WAVs are big and MP3s are small
A WAV stores every sample of the sound, 44,100 or 48,000 numbers per second for each channel, with nothing thrown away. That's ideal while you record and edit, and unwieldy when you want to email a demo, publish an episode or fill a phone with music.
MP3 shrinks the file by leaving out what your ears are unlikely to notice: quiet sounds hidden behind louder ones, detail at the edges of hearing. How much is kept depends only on the bitrate you pick, so a five-minute WAV converted at 192 kbps always comes out at about 7 MB.
Picking a bitrate for the job
- 128 kbps, spoken word: voice memos, interviews, mono podcasts. Small, and perfectly clear for speech.
- 192 kbps, demos, rough mixes and podcasts with music. On everyday speakers, few listeners could pick it out from the WAV.
- 256 to 320 kbps, finished music and anything you'll publish. 320 kbps is as high as MP3 goes.
Choosing mono doesn't shrink the MP3 at a given bitrate, but every bit then describes a single channel, so a mono voice track at 128 kbps sounds very clean.
Working to a spec? Podcast hosts, voice-over clients and radio producers sometimes ask for something like “128 kbps, mono, 44.1 kHz”. Set the bitrate, then choose Mono and 44.1 kHz under Sample rate and channels, and every file in the batch follows it.
One exception to all this: sounds that must loop seamlessly, like game audio or website ambience. MP3 adds a sliver of silence at the start and end, which can make a loop hiccup, so keep those as WAV or try OGG.
Sample rate, bit depth and big batches
Bit depth doesn't carry over into an MP3, so 24-bit and 32-bit float WAVs convert just like 16-bit ones. The sample rate is kept as long as it's 48 kHz or lower; high-resolution recordings at 88.2 or 96 kHz are brought down to 48 kHz, the most an MP3 can hold. Prefer 44.1 kHz? Set it under Sample rate and channels.
For a batch, drop in everything at once. Files convert one after another, each with its own progress bar, and an unreadable file is simply flagged while the others carry on. When they're finished, Download all packs them into one ZIP.
Keep the WAV as your master
Treat the MP3 as a delivery copy. Hold on to the WAV, and if you ever need a different bitrate or format, convert from it again rather than from the MP3. Since each MP3 keeps its WAV's name with a new ending, tidy the file names first and the batch arrives ready to publish.
It's worth setting the level before you convert, too: Normalize Audio brings a mix or an episode to −14 or −16 LUFS and can save the MP3 for you. For trims and fades, use the audio editor. Need to go the other way? See MP3 to WAV.