If you've used iTunes, Spotify, YouTube, or any Apple device in the last 20 years, you've heard AAC — probably without knowing it. MP3 is older and universally recognized. AAC is newer and technically superior. Which one you should use depends on where your audio is going.
How both formats work
Both MP3 and AAC are lossy audio codecs. They reduce file size by discarding audio information the human ear is least likely to perceive — sounds masked by louder sounds, frequencies at the edges of hearing, and subtle spatial information. This process is called perceptual coding, and it's what makes both formats so much smaller than uncompressed WAV or AIFF.
The difference is efficiency. AAC (Advanced Audio Coding) was designed in 1997 as a successor to MP3, with improvements to the underlying compression algorithm. At the same bitrate, AAC retains more audio detail.
Sound quality comparison
The general consensus among audio engineers and in double-blind listening tests:
128 kbps AAC ≈ 160–192 kbps MP3 in perceived quality.
That's a meaningful difference. An AAC file at 128 kbps sounds noticeably cleaner than an MP3 at the same bitrate — you'll hear this most clearly in high-frequency content like cymbals, acoustic guitar strumming, and vocals with sibilance (the "s" and "sh" sounds). MP3's weaknesses at low bitrates are well-documented: a kind of underwater, smeared quality sometimes called "pre-echo."
At 320 kbps — the maximum for MP3 and commonly used for high-quality encodes — the difference between MP3 and AAC is very small and most listeners can't distinguish them in blind tests. Both are considered transparent (indistinguishable from lossless) for most content at this bitrate.
Bitrate guide
| Bitrate | MP3 quality | AAC quality | Typical use |
|---|---|---|---|
| 64 kbps | Poor | Acceptable | Podcasts, voice only |
| 128 kbps | Acceptable | Good | General music, streaming |
| 192 kbps | Good | Very good | Higher-quality streaming |
| 256 kbps | Very good | Excellent | Apple Music, YouTube |
| 320 kbps | Excellent | Excellent | Local high-quality libraries |
Apple Music streams at 256 kbps AAC. Spotify uses 320 kbps OGG Vorbis (another format in the same family as AAC) for its "very high" tier. YouTube uses AAC for its audio tracks.
Compatibility: where each format works
MP3: - Universal — plays on every device, every software player, every car stereo, every streaming platform - No licensing issues for playback (patents have expired) - The safest choice if you don't know what will play the file
AAC: - Native format for Apple devices (iPhone, iPad, Mac, iPod, Apple TV) - Supported by Chrome, Firefox, Safari, Edge - Supported by Android and most modern devices - Not supported by some older MP3-only hardware (car stereos from the early 2000s, basic portable players)
The compatibility gap has largely closed. Most devices made after 2010 support AAC. But if you're distributing audio and can't control the playback environment — old car stereos, legacy media players, industrial or embedded systems — MP3 is still the safer bet.
When to use each format
Choose AAC when: - You're making content for Apple devices or services - You want the best quality at a given file size - You're building a music library on iTunes/Music - You're uploading to YouTube or a platform that supports AAC
Choose MP3 when: - You need guaranteed compatibility with everything - You're submitting audio to a platform that requires MP3 specifically - You're distributing to an audience with unknown playback hardware - You want the widest possible support without any exceptions
Should you convert your existing MP3 library to AAC?
No. Converting a lossy MP3 to AAC is called transcoding, and it's lossy-to-lossy — you're starting from an already-compressed signal and compressing it again. The output will be worse than the original MP3, not better. You'd be adding a second generation of compression artifacts on top of the first.
If you have lossless originals (FLAC, WAV, AIFF), convert those to AAC. If you only have MP3s, keep them as MP3s.
Converting audio on Converthor
Converthor can convert between audio formats including MP3 to AAC, AAC to MP3, and other common formats. Conversion runs server-side, no account required, and files are deleted immediately after processing.
The bottom line
AAC is the better-sounding format at every bitrate below 320 kbps. If you're building new audio files and your audience has modern devices, AAC is the right choice. MP3 remains valuable when you need absolute compatibility with no exceptions. For most people in 2026, AAC is the better default — and the reason Apple, YouTube, and most streaming services made that switch years ago.