A three-minute song recorded at high quality can easily be 30–50 MB. That's fine for archiving, but not for sending over email, uploading to a podcast host, or embedding in a presentation. Compression brings it down to 3–5 MB with no audible difference in most listening environments.
Here's what's actually happening, and how to do it well.
Lossy vs. Lossless: What You're Actually Choosing
There are two kinds of audio compression, and they work very differently.
Lossless compression (FLAC, ALAC) reduces file size without discarding any audio data. A FLAC file sounds identical to the original WAV because all the information is preserved — it's just stored more efficiently. File size reduction is modest: usually 40–60%.
Lossy compression (MP3, AAC, OGG) achieves much smaller files by permanently removing audio data your ears are unlikely to notice — high-frequency content, sounds masked by louder sounds, spatial information below the threshold of perception. Done right, the difference is inaudible on typical speakers and headphones. Done wrong, you get the metallic warbling sound that became associated with low-quality MP3s in the early 2000s.
For almost all practical purposes — podcasts, music for video, voice memos, email attachments — lossy compression at an appropriate bitrate is the right call.
Choosing the Right Bitrate
Bitrate determines how much data per second is used to represent the audio. Higher bitrate = larger file + better quality.
| Use case | Recommended bitrate | |----------|-------------------| | Voice / podcasts | 64–96 kbps | | Music (casual listening) | 128 kbps | | Music (good headphones) | 192 kbps | | High-fidelity archive | 320 kbps |
For stereo music you intend to share or publish, 128 kbps AAC or 192 kbps MP3 is the practical sweet spot — files are small, quality is indistinguishable from the source on anything but audiophile equipment.
Going below 96 kbps for music introduces compression artifacts that most people can hear: a swirling or metallic quality on cymbals and high-frequency instruments.
How to Compress an Audio File
The Audio Compressor on this site runs entirely in your browser using FFmpeg — no upload, no account, no file size limits imposed by a third-party server.
- Drop your file in (MP3, WAV, FLAC, AAC, OGG, M4A all work)
- Pick your output format and bitrate preset
- Download the compressed file
The tool shows you the output file size before you download so you can adjust if needed.
One Thing Most People Get Wrong
Compressing an already-compressed file makes quality worse, not better. If you have a 128 kbps MP3 and re-compress it to 128 kbps MP3, the result will be lower quality than the original — you're encoding artifacts from the first pass along with the audio.
If you need to compress an existing MP3, either compress to a significantly lower bitrate (accepting the quality tradeoff) or go back to the original uncompressed source if you have it. Always start compression from the highest-quality version available.
When to Keep the Original
For anything you might edit later — podcast raw recordings, music you're producing, voice-overs — keep the uncompressed WAV or lossless file. Compress only the final export. Editing compressed audio, then re-compressing for output, stacks quality loss in a way that adds up fast.
Format by Format: What Actually Differs
The bitrate table above tells you how much data to use. The format choice tells you how that data is encoded. They're separate decisions.
MP3 — The oldest and most universally supported lossy format. Works on every device, every platform, and every piece of audio software made in the last 25 years. At 192 kbps it sounds excellent. The main reason to choose MP3 over AAC today is compatibility with very old hardware.
AAC — The successor to MP3. At the same bitrate, AAC sounds noticeably cleaner — especially on cymbals, reverb tails, and high-frequency content. It's the default format for Apple Music, iTunes, and most streaming services. For any new file where you control the format, AAC is the better choice.
OGG Vorbis — Open source with good quality-to-size ratio. Common in games and web applications. Broad browser support for streaming. Not natively supported by all standalone audio players.
FLAC — Lossless. Sounds identical to the original WAV. Files are 40–60% smaller than uncompressed WAV but still several times larger than MP3 or AAC at equivalent listening quality. Use FLAC for archiving masters and anything you plan to edit later.
WAV — Uncompressed. The largest files, perfect quality. The right working format during production. Not the right choice for anything that will be shared, streamed, or embedded.
M4A — Functionally AAC in an MPEG-4 container. Identical to AAC for playback purposes. Common output from iOS voice memos and GarageBand exports.
For sharing or distribution: AAC if you choose the format, MP3 if you need maximum compatibility. For archiving: FLAC if storage isn't a concern, 320 kbps MP3 or AAC if it is.
Compression for Specific Workflows
Podcast episodes — Record in WAV or FLAC, edit in that format, export as AAC or MP3 for distribution. Most podcast platforms accept MP3 at 128 kbps for a single voice, 192 kbps for interviews or music beds. Stereo is only necessary if the content has meaningful stereo information — a solo voice recording gains nothing from stereo and doubles the file size versus mono.
Music for video — The audio track in a video file is usually AAC or MP3. If you're adding a music track to a video project, compress it before adding it to keep the overall export size down. 128 kbps AAC is plenty for background music that competes with dialogue and sound effects.
Voice memos and meetings — 64 kbps mono AAC captures speech clearly and produces small files. A one-hour meeting recording at this setting is roughly 30 MB — compared to 3.5 GB for the same recording in uncompressed WAV.
Music for streaming — If you're distributing music through Spotify, Apple Music, or similar platforms, they re-encode your upload anyway. Upload at the highest quality you have (lossless or 320 kbps). The platform's encoder produces the final streaming file.
Related Audio Tools
If the file is longer than you need, the Audio Clipper lets you trim it to a specific region before compressing — which reduces the file size further without touching quality settings. For converting between formats entirely (MP3 to AAC, WAV to OGG), the Audio Converter handles the full range. If you're starting from a video file and only need the audio track, Video to Audio extracts it first so you're only compressing the audio you actually need.
Frequently Asked Questions
What is the best format for compressed audio?
AAC at 128 kbps is the best all-around choice for compressed audio — it sounds better than MP3 at the same bitrate and is supported on every major platform. MP3 at 192 kbps is a solid alternative if you need the widest compatibility. For voice-only content like podcasts, 96 kbps AAC is indistinguishable from higher bitrates.
How much can I compress audio without it sounding worse?
For music, most people cannot hear a difference between the original and 128 kbps AAC or 192 kbps MP3 on typical headphones or speakers. Going below 96 kbps for music introduces audible artifacts — a metallic or swirling quality on high-frequency sounds. For voice recordings, you can compress further: 64–96 kbps is enough for podcasts and voice memos.
Does the Audio Compressor upload my files to a server?
No. The Audio Compressor runs entirely in your browser using a WebAssembly build of FFmpeg. Your audio files are processed locally and never transmitted to any server. There is no account required and no file size limit imposed by a third party.
What is the difference between MP3 and AAC?
Both are lossy compression formats, but AAC is the newer standard and achieves better quality at the same file size. AAC at 128 kbps sounds noticeably cleaner than MP3 at 128 kbps, particularly on high-frequency content. MP3 has been around since the 1990s and has broader compatibility with older devices and software.
Can I compress an audio file that is already compressed?
You can, but quality degrades further with each compression pass. If you have a 128 kbps MP3 and re-compress it to 128 kbps, the result will be lower quality than the original — artifacts from the first pass get encoded alongside the audio. Always start from the highest-quality source you have. If that means a re-compressed file, compress to a significantly lower bitrate rather than the same one.
Quick Checklist
- [ ] Identified whether you need lossy or lossless compression
- [ ] Chose a bitrate appropriate for the use case (voice vs. music)
- [ ] Started from the highest-quality source available, not a re-compressed copy
- [ ] Checked the output file size before downloading
- [ ] Kept the original uncompressed file if you'll need to edit later