Bitrate is the amount of data used per second of audio, measured in kilobits per second (kbps). File size in MB = (Bitrate in kbps × Duration in seconds) ÷ 8000. For example, a 3-minute (180-second) audio file at 128 kbps = (128 × 180) ÷ 8000 = 2.88 MB. The same file at 320 kbps = 7.2 MB. Halving the bitrate roughly halves the file size, but with some quality cost.
Free Online Audio Compressor
Reduce Audio File Size Without Quality Loss
Compress large audio files to a fraction of their size by adjusting the output bitrate. Perfect for email attachments, web delivery, podcast hosting, and saving storage space on your device.
Reduce file size by up to 90%
Choose output bitrate precisely
Supports all major audio formats
Drop your file here
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Up to 100 MB free • Outputs: MP3, AAC, OGG
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Files deleted in 2h
Fast processing
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Simple & Fast
How to Use Audio Compressor
Convert your files in three simple steps — no software, no signup.
01
Upload Your Audio
Upload a large WAV, FLAC, MP3, AAC, or other audio file that you want to compress to a smaller size.
02
Select Target Bitrate
Choose your desired output bitrate: 64kbps for voice/podcasts, 128kbps for general music, or 192kbps for quality-conscious compression.
03
Download Compressed File
Download your compressed audio file. Compare the input and output file sizes to see how much space you saved.
Features
Why Use Audio Compressor?
Save Storage Space
Convert large WAV or FLAC files to compressed MP3 at your chosen bitrate and save up to 90% of disk or cloud storage space.
Email-Ready Files
Compress audio files below typical email attachment limits (10–25 MB) for easy sharing without file transfer services.
Web-Optimised Audio
Reduce audio file sizes for faster web page loading and reduced bandwidth consumption on web and mobile apps.
Podcast Optimisation
Podcast hosting platforms have storage and bandwidth limits. Compress episodes to 96–128kbps MP3 to reduce hosting costs without sacrificing listener experience.
Fine-Grained Control
Choose from a range of bitrate options to precisely balance audio quality and output file size for your specific use case.
Secure Processing
Files are processed in a sandboxed environment and automatically deleted within one hour. Your content stays private.
Compatibility
Supported Formats
All the formats you need, all in one place.
| Format | Description | Extension | Best Used For |
|---|---|---|---|
| WAV → MP3 64K | Extreme compression for voice-only content | .wav |
Voice memos, speech recordings, dictation |
| WAV → MP3 128K | Good quality, significant size reduction | .wav |
Podcasts, audiobooks, general music |
| WAV → MP3 192K | High quality with moderate compression | .wav |
Music streaming, presentations |
| FLAC → AAC 128K | Lossless to efficient streaming format | .flac |
Apple device delivery, streaming services |
| MP3 → MP3 64K | Downscale existing MP3 to smaller size | .mp3 |
Podcast archive compression |
| M4A → MP3 96K | Compress Apple audio for broad sharing | .m4a |
Voice memo sharing, meeting audio |
| OGG → OGG LOW | Re-encode OGG at lower quality level | .ogg |
Web game audio optimisation |
FAQ
Frequently Asked Questions
For spoken-word podcasts, 96kbps mono MP3 is the sweet spot — it sounds clear and keeps file sizes small for hosting. For music podcasts or high-quality shows, use 128kbps stereo.
A 3-minute WAV file (~30 MB) can be compressed to about 2.8 MB at 128kbps MP3 — a 90% reduction. At 64kbps it drops to 1.4 MB. The exact ratio depends on the source format and chosen bitrate.
At 128kbps or above, most listeners cannot detect the difference for casual listening. At 64kbps, audio sounds "thinner" and is best reserved for speech content. We recommend listening to a test clip before compressing a large library.
Yes. Uploading a FLAC file and selecting an MP3 or AAC output bitrate will produce a compressed lossy version. This is a common workflow for creating distribution copies from a lossless master.
Yes — re-compressing a lossy file introduces generation loss. Each compression step discards more audio data. Where possible, always compress from a lossless source (WAV or FLAC).
This tool performs file-size compression — reducing bitrate to shrink file size. Dynamic range compression (used in music mastering) controls volume levels and is a different audio processing effect.
Real-World Uses
Who Uses Audio Compressor?
From everyday users to professionals — see how people rely on this tool every day.
Office Worker
Compress Audio for Email Attachments
Reduce a 30 MB WAV recording to under 5 MB MP3 so it fits within common email attachment size limits without a file-sharing service.
Podcast Host
Optimise Episode Files for Podcast Hosts
Compress each episode to 128 kbps mono MP3 to stay within Buzzsprout, Anchor, and Libsyn storage and bandwidth limits while maintaining quality.
Web Developer
Reduce Audio Assets for Faster Pages
Compress background music and sound effects to 64–96 kbps OGG or AAC to cut web page load times and reduce mobile data usage.
Mobile User
Free Up Storage on Your Device
Convert large WAV or FLAC music files to 192 kbps MP3 and save significant space on a phone without a noticeable quality change.
Cloud Storage User
Reduce Cloud Storage Costs
A 1 TB music library in WAV can shrink to under 100 GB in 256 kbps AAC — cutting cloud storage costs by 90% with transparent audio quality.
Streaming Creator
Prepare Audio for Streaming Platforms
Streaming platforms transcode your uploads anyway. Pre-compress to 256 kbps AAC to match their standard and avoid double transcoding artefacts.
Why TransmuteBox?
TransmuteBox vs. Alternatives
See how we compare to desktop software and other online converters.
| Feature |
Our Tool TransmuteBox |
Desktop App | Other Online |
|---|---|---|---|
| Adjustable bitrate | |||
| Multiple output formats | |||
| Lossless → lossy compression | |||
| Size preview estimate | |||
| No software install | |||
| Mobile browser support | |||
| Free to use |
Under the Hood
Technical Specifications
Built on industry-standard open-source tools for maximum quality and reliability.
Limits & Restrictions
- Max file size: 500 MB
- Bitrate options: 32 / 64 / 96 / 128 / 192 / 256 / 320 kbps
- Output: MP3, AAC, OGG, OPUS
FFmpeg
MP3
AAC
OGG
Bitrate
Compression
Conversion Engine
FFmpeg 6.x · libmp3lame (MP3), libfdk-aac (AAC), libvorbis (OGG)
Output Quality
Output bitrate range: 32–320 kbps; sample rate preserved from source
Average Speed
Typical compress of 100 MB WAV to MP3: 5–15 seconds
Data Security
HTTPS transfer · isolated temp dir · auto-purged in 2 h
Bitrate Range
32–320 kbps
Typical Saving
Up to 90% smaller
Output Fmts
MP3, AAC, OGG, OPUS
Auto-Delete
2 hours
Complete Guide
Audio File Compression: Bitrate, Quality, and File Size Explained
When people talk about compressing audio files, they usually mean reducing bitrate to shrink file size — not the dynamic range compression used in music production. Understanding how bitrate affects file size and perceptual quality helps you choose the right compression settings for every use case.
How Bitrate Determines File Size
Choosing the Right Bitrate for Your Content
Not all audio content needs the same bitrate. Speech is much more forgiving than music because it occupies a narrower frequency range and listeners are less sensitive to artefacts in the voice frequency band. Music requires higher bitrates to preserve high-frequency detail (cymbals, reverb tails, acoustic instruments).
- Speech / podcasts: 64–96 kbps mono is excellent — clear, intelligible, very small files.
- General music (casual listening): 128 kbps sounds good to most listeners.
- Music (quality-conscious): 192 kbps is noticeably better, recommended for music podcasts.
- Transparent quality: 256 kbps AAC or 320 kbps MP3 — indistinguishable from lossless for most people.
Generation Loss: Why Source Quality Matters
Every re-encoding of a lossy audio file removes more audio data. Converting an MP3 at 128 kbps to AAC at 128 kbps does not produce a better file — it introduces artefacts from both encode stages on top of each other. To avoid generation loss, always compress from a lossless source (WAV or FLAC) whenever possible. If you only have a lossy source, compress to the same or higher bitrate — never lower — to avoid noticeable degradation.
MP3 vs AAC vs OGG for Compression
All three are lossy codecs but with different efficiencies. At equivalent bitrates: OGG Vorbis and AAC both outperform MP3 technically. AAC at 128 kbps typically sounds as good as MP3 at 160 kbps. OGG at quality 5 (~160 kbps VBR) sounds as good as MP3 at 192–224 kbps. For maximum quality at a given file size target, choose AAC (for Apple/web) or OGG (for open-source/game). Use MP3 only when broad legacy compatibility is the priority.
Podcast and Streaming Platform Recommendations
Different platforms have different audio requirements and transcode your uploads on arrival. If you upload a high-bitrate file, the platform transcodes it to their standard. If you upload a low-bitrate file, the platform transcodes from an already-degraded source. Best practice: upload at or above the platform's output bitrate to avoid double transcoding. Spotify outputs up to 320 kbps; upload at least 256 kbps. YouTube uses 126 kbps AAC; uploading at 256 kbps AAC is sufficient. Apple Podcasts recommends 128 kbps stereo M4A. Match these targets with your compressed output.