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Supported Formats
Convert between all major file formats with high quality
Common Formats
MPEG-1 Audio Layer III - the most universal audio format worldwide, using lossy compression to reduce file sizes by 90% while maintaining excellent perceived quality. Perfect for music libraries, podcasts, portable devices, and any scenario requiring broad compatibility. Supports bitrates from 32-320kbps. Standard for digital music since 1993, playable on virtually every device and platform.
Waveform Audio File Format - uncompressed PCM audio providing perfect quality preservation. Standard Windows audio format with universal compatibility. Large file sizes (10MB per minute of stereo CD-quality). Perfect for audio production, professional recording, mastering, and situations requiring zero quality loss. Supports various bit depths (16, 24, 32-bit) and sample rates. Industry standard for professional audio work.
Ogg Vorbis - open-source lossy audio codec offering quality comparable to MP3/AAC at similar bitrates. Free from patents and licensing restrictions. Smaller file sizes than MP3 at equivalent quality. Used in gaming, open-source software, and streaming. Supports variable bitrate (VBR) for optimal quality. Perfect for applications requiring free codecs and good quality. Growing support in media players and platforms.
Advanced Audio Coding - successor to MP3 offering better quality at same bitrate (or same quality at lower bitrate). Standard audio codec for Apple devices, YouTube, and many streaming services. Supports up to 48 channels and 96kHz sample rate. Improved frequency response and handling of complex audio. Perfect for iTunes, iOS devices, video streaming, and modern audio applications. Part of MPEG-4 standard widely supported across platforms.
Free Lossless Audio Codec - compresses audio 40-60% without any quality loss. Perfect bit-for-bit preservation of original audio. Open-source format with no patents or licensing fees. Supports high-resolution audio (192kHz/24-bit). Perfect for archiving music collections, audiophile listening, and scenarios where quality is paramount. Widely supported by media players and streaming services. Ideal balance between quality and file size.
MPEG-4 Audio - AAC or ALAC audio in MP4 container. Standard audio format for Apple ecosystem (iTunes, iPhone, iPad). Supports both lossy (AAC) and lossless (ALAC) compression. Better quality than MP3 at same file size. Includes metadata support for artwork, lyrics, and rich tags. Perfect for iTunes library, iOS devices, and Apple software. Widely compatible across platforms despite Apple association. Common format for purchased music and audiobooks.
Windows Media Audio - Microsoft's proprietary audio codec with good compression and quality. Standard Windows audio format with native OS support. Supports DRM for protected content. Various profiles (WMA Standard, WMA Pro, WMA Lossless). Comparable quality to AAC at similar bitrates. Perfect for Windows ecosystem and legacy Windows Media Player. Being superseded by AAC and other formats. Still encountered in Windows-centric environments and older audio collections.
Lossless Formats
Apple Lossless Audio Codec - Apple's lossless compression reducing file size 40-60% with zero quality loss. Perfect preservation of original audio like FLAC but in Apple ecosystem. Standard lossless format for iTunes and iOS. Supports high-resolution audio up to 384kHz/32-bit. Smaller than uncompressed but larger than lossy formats. Perfect for iTunes library, audiophile iOS listening, and maintaining perfect quality in Apple ecosystem. Comparable to FLAC but with better Apple integration.
Monkey's Audio - high-efficiency lossless compression achieving better ratios than FLAC (typically 55-60% of original). Perfect quality preservation with zero loss. Free format with open specification. Slower compression/decompression than FLAC. Popular in audiophile communities. Limited player support compared to FLAC. Perfect for archiving when maximum space savings desired while maintaining perfect quality. Best for scenarios where storage space is critical and processing speed is not.
WavPack - hybrid lossless/lossy audio codec with unique correction file feature. Can create lossy file with separate correction file for lossless reconstruction. Excellent compression efficiency. Perfect for flexible audio archiving. Less common than FLAC. Supports high-resolution audio and DSD. Convert to FLAC for universal compatibility.
True Audio - lossless audio compression with fast encoding/decoding. Similar compression to FLAC with simpler algorithm. Open-source and free format. Perfect quality preservation. Less common than FLAC with limited player support. Perfect for audio archiving when FLAC compatibility not required. Convert to FLAC for broader compatibility.
Audio Interchange File Format - Apple's uncompressed audio format, equivalent to WAV but for Mac. Stores PCM audio with perfect quality. Standard audio format for macOS and professional Mac audio applications. Supports metadata tags better than WAV. Large file sizes like WAV (10MB per minute). Perfect for Mac-based audio production, professional recording, and scenarios requiring uncompressed audio on Apple platforms. Interchangeable with WAV for most purposes.
Modern Formats
Opus Audio Codec - modern open-source codec (2012) offering best quality at all bitrates from 6kbps to 510kbps. Excels at both speech and music. Lowest latency of modern codecs making it perfect for VoIP and real-time communication. Superior to MP3, AAC, and Vorbis at equivalent bitrates. Used by WhatsApp, Discord, and WebRTC. Ideal for streaming, voice calls, podcasts, and music. Becoming the universal audio codec for internet audio.
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Matroska Audio - audio-only Matroska container supporting any audio codec. Flexible format with metadata support. Can contain multiple audio tracks. Perfect for audio albums with chapters and metadata. Part of Matroska multimedia framework. Used for audiobooks and multi-track audio. Convert to FLAC or MP3 for universal compatibility.
Legacy Formats
MPEG-1 Audio Layer II - predecessor to MP3 used in broadcasting and DVDs. Better quality than MP3 at high bitrates. Standard audio codec for DVB (digital TV) and DVD-Video. Lower compression efficiency than MP3. Perfect for broadcast applications and DVD authoring. Legacy format being replaced by AAC in modern broadcasting. Still encountered in digital TV and video production workflows.
Dolby Digital (AC-3) - surround sound audio codec for DVD, Blu-ray, and digital broadcasting. Supports up to 5.1 channels. Standard audio format for DVDs and HDTV. Good compression with multichannel support. Perfect for home theater and video production. Used in cinema and broadcast. Requires Dolby license for encoding.
Adaptive Multi-Rate - speech codec optimized for mobile voice calls. Excellent voice quality at very low bitrates (4.75-12.2 kbps). Standard for GSM and 3G phone calls. Designed specifically for speech, not music. Perfect for voice recordings, voicemail, and speech applications. Used in WhatsApp voice messages and mobile voice recording. Efficient for voice but inadequate for music.
Sun/NeXT Audio - simple audio format from Sun Microsystems and NeXT Computer. Uncompressed or μ-law/A-law compressed audio. Common on Unix systems. Simple header with audio data. Perfect for Unix audio applications and legacy system compatibility. Found in system sounds and Unix audio files. Convert to WAV or MP3 for modern use.
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RealAudio - legacy streaming audio format from RealNetworks (1990s-2000s). Pioneered internet audio streaming with low-bitrate compression. Obsolete format replaced by modern streaming technologies. Poor quality by today's standards. Convert to MP3 or AAC for modern use. Historical importance in early internet audio streaming.
Specialized Formats
DTS Coherent Acoustics - surround sound codec competing with Dolby Digital. Higher bitrates than AC-3 with potentially better quality. Used in DVD, Blu-ray, and cinema. Supports up to 7.1 channels and object-based audio. Perfect for high-quality home theater. Premium audio format for video distribution. Convert to AC-3 or AAC for broader compatibility.
Core Audio Format - Apple's container for audio data on iOS and macOS. Supports any audio codec and unlimited file sizes. Modern replacement for AIFF on Apple platforms. Perfect for iOS app development and professional Mac audio. No size limitations (unlike WAV). Can store multiple audio streams. Convert to M4A or MP3 for broader compatibility outside Apple ecosystem.
VOC (Creative Voice File) - audio format from Creative Labs Sound Blaster cards. Popular in DOS era (1989-1995) for games and multimedia. Supports multiple compression formats and blocks. Legacy PC audio format. Common in retro gaming. Convert to WAV or MP3 for modern use. Important for DOS game audio preservation.
Speex - open-source speech codec designed for VoIP and internet audio streaming. Variable bitrate from 2-44 kbps. Optimized for speech with low latency. Better than MP3 for voice at low bitrates. Being superseded by Opus. Perfect for voice chat, VoIP, and speech podcasts. Legacy format replaced by Opus in modern applications.
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How to Convert Files
Upload your files, select output format, and download converted files instantly. Our converter supports batch conversion and maintains high quality.
Frequently Asked Questions
What is AU audio format and where did it come from?
AU (also called SND) is a simple audio file format developed by Sun Microsystems for Unix workstations in the 1980s. It was also used by NeXT computers (Steve Jobs' company between Apple stints). AU files contain uncompressed or μ-law/A-law compressed audio with a simple header. Think of it as the Unix equivalent of WAV (Windows) or AIFF (Mac).
Technical simplicity: AU format has minimal header (24 bytes minimum), supports various encodings (PCM, μ-law, A-law, ADPCM), and uses big-endian byte order (Unix standard). This simplicity made it popular for Unix systems and telephony applications where low overhead mattered. It's more primitive than WAV but that was the point - simple and functional.
Should I convert AU files to WAV or MP3?
Convert AU files for better compatibility:
Modern Software Support
Most modern audio software doesn't prioritize AU support. WAV/MP3 work everywhere. Better compatibility.
Obsolete Format
AU is Unix legacy format with no advantages over modern alternatives. Convert for future-proofing.
Mobile Incompatibility
Phones don't support AU. Converting to MP3/AAC enables mobile playback. Essential for portability.
Standard Formats Better
WAV (uncompressed) or FLAC (lossless) are better archival formats. MP3/AAC better for compressed. AU offers nothing.
Convert AU to WAV if quality matters, MP3 if size matters. No reason to maintain AU files in modern workflow.
Does converting AU to WAV lose quality?
AU to WAV quality considerations:
Depends on Encoding
AU with PCM is uncompressed - converts to WAV losslessly. AU with μ-law/A-law is lossy compressed telephony audio.
PCM Conversion
PCM AU to WAV is just container change. Bit-perfect audio transfer. Zero quality loss. Same raw audio data.
μ-law/A-law Conversion
These are lossy 8-bit compression for telephony (8kHz). Already degraded. Converting to WAV doesn't improve quality.
Byte Order Change
AU uses big-endian, WAV uses little-endian. Conversion swaps bytes but audio is mathematically identical.
Header Difference
Only file header changes (AU vs WAV structure). Audio payload transfers perfectly for uncompressed types.
Best Practice
Convert PCM AU to WAV for lossless modern format. Convert telephony AU to MP3 for practical compressed format.
No Generation Loss
For uncompressed AU, conversion is completely safe. No quality concerns. Format compatibility gain with zero cost.
AU to WAV conversion is safe for PCM audio. Already-compressed AU can't get better, convert to practical format.
What is μ-law and A-law compression in AU files?
μ-law (mu-law) and A-law are logarithmic compression algorithms for telephone audio, reducing 13-16 bit audio to 8 bits. They're lossy compression optimized for human speech, not music. μ-law is used in North America/Japan (T1 telephony), A-law in Europe/rest of world (E1 telephony). Both achieve ~2:1 compression with acceptable voice quality.
How it works: Logarithmic encoding compresses dynamic range - loud sounds get less precision, quiet sounds get more. This matches human hearing (logarithmic sensitivity) and preserves intelligibility of speech. Quality is poor by music standards (muffled, compressed) but acceptable for voice communication.
Practical impact: If your AU file uses μ-law or A-law, it's already degraded telephony-quality audio (typically 8kHz, 8-bit). Converting to WAV or MP3 won't improve quality - source is fundamentally limited. These encodings were designed for 1980s telephone systems, not high-fidelity audio.
What software can play and convert AU files?
Players: VLC (Windows/Mac/Linux - plays everything including AU), Audacity (import/edit AU files), QuickTime Player (Mac - native AU support), Windows Media Player (with codecs), mpv (minimalist player). Most full-featured audio software handles AU because it's simple format, but support isn't guaranteed in lightweight players.
Converters: FFmpeg (command line - `ffmpeg -i input.au output.wav` or `output.mp3`), Audacity (GUI import/export), SoX (command-line audio Swiss army knife), foobar2000 (Windows), XLD (Mac). AU is well-supported by professional audio tools despite obscurity.
Online: Our converter and others support AU format. Upload .au file, choose WAV/MP3/AAC output, download. Easy for occasional conversions without installing software. For batch processing old Unix archives, FFmpeg with scripts is most efficient.
Why was AU format used on Unix systems?
Simplicity: AU format is extremely simple - 24-byte header with offset, sample rate, channels, encoding type. No complex structures or specifications. This matched Unix philosophy of simple, composable tools. Easy to implement, easy to parse, minimal overhead.
Native Unix format: Sun workstations dominated Unix market in 1980s-90s. Sun's audio format became de facto Unix standard. NeXT also used AU, spreading it further. When you recorded audio on Unix workstation, you got AU file. It was the native format, like WAV on Windows.
Telephony use: μ-law compression in AU made it perfect for telephony applications on Unix servers. Many PBX systems, IVR platforms, and telecom tools used AU format for voice prompts and recordings. This kept AU relevant in telephony even after general-purpose audio moved to better formats.
Can AU files contain high-quality audio?
Yes, AU supports uncompressed PCM audio at various sample rates and bit depths. You can have 16-bit/44.1kHz stereo AU files with CD-quality audio. However, most AU files you encounter are either μ-law/A-law compressed (telephony quality) or low sample rate (8kHz voice recordings). High-quality AU was technically possible but uncommon.
Practical reality: Unix systems recording high-quality audio typically used other formats. AU was mainly for system sounds, voice recordings, and telephony. If you have high-quality AU file, someone deliberately chose AU over alternatives - probably for compatibility with specific Unix software.
Modern perspective: Even if AU contains high-quality PCM, convert to WAV or FLAC. These formats have better software support, clearer specifications, and wider compatibility. AU offers no advantages for high-quality audio - it's legacy format without modern benefits.
How do I batch convert AU files?
Batch AU conversion methods:
FFmpeg (Best)
Windows: `for %f in (*.au) do ffmpeg -i "%f" "%~nf.wav"` converts folder. Linux/Mac: similar with bash.
SoX (Unix Tool)
`for f in *.au; do sox "$f" "${f%.au}.wav"; done` processes all AU files. Fast, reliable.
GUI Batch
Audacity (macros), foobar2000 (Windows batch convert), XLD (Mac batch mode). Easier for non-technical users.
Compression Choice
Convert to WAV for archival (uncompressed). Convert to 192kbps MP3 for practical use (compressed).
Verify First File
Test conversion on one AU file before batch processing hundreds. Ensure settings correct.
FFmpeg or SoX handle AU well. Batch convert old Unix archives to modern formats for better accessibility.
What's the difference between AU and WAV?
Origins: AU from Sun/Unix (1980s), WAV from Microsoft/IBM (1991 RIFF/WAV specification). Platform differences - AU used big-endian byte order (Unix/Mac standard), WAV uses little-endian (PC standard). Both can contain similar audio data (PCM, ADPCM, etc.).
Structure: AU has simpler header (24 bytes minimum, extensible), WAV has more complex RIFF structure with chunks. AU is more minimalist, WAV is more flexible with metadata. For basic uncompressed audio, they're functionally equivalent - different containers for same audio data.
Practical use: WAV won due to Windows dominance and better standardization. AU survives only in Unix legacy systems and telephony. If choosing today, always use WAV (or FLAC for lossless compression) - better support, clearer specs, universal compatibility. AU is historical curiosity.
Are there any reasons to keep AU format files?
When to keep AU vs convert:
Legacy System Compatibility
If feeding audio to old Unix software that expects AU format specifically. Some vintage systems reject other formats.
Telephony Systems
Some PBX/IVR platforms require AU with μ-law. Converting breaks compatibility. Keep originals for these.
Historical Archives
If archiving original Unix system content, keep AU for historical accuracy. But make modern copies too.
Otherwise Convert
For personal audio collections, music, or general use - convert to WAV/MP3. No benefit to keeping AU.
Dual Approach
Archive AU originals if historically important, but create WAV/MP3 copies for actual use. Best of both worlds.
Modern Workflows
Zero reason to create new AU files. Use WAV (uncompressed), FLAC (lossless), or AAC/MP3 (lossy).
Format Has No Future
AU support will only decrease. Converting now ensures long-term accessibility. Don't rely on obsolete format.
Niche Applications Only
Unless you have specific Unix/telephony needs, AU is dead format. Convert and move to modern standards.
Simple Decision
No specific reason to keep AU? Convert it. Have specific legacy need? Keep AU copy. Context determines choice.
Future-Proofing
Software support for AU will disappear. Converting ensures your audio remains playable decades from now.
What sample rates and bit depths does AU support?
AU format is flexible: supports sample rates from 8kHz (telephony) to 48kHz+ (high quality), bit depths from 8-bit to 24-bit, and mono or stereo channels. Common configurations: 8kHz/8-bit/μ-law (telephone quality), 22.05kHz/16-bit (multimedia), 44.1kHz/16-bit (CD quality), 48kHz/16-bit (video audio).
However, most AU files in the wild are low-quality telephony audio (8kHz/8-bit) because that's what AU was primarily used for. High-quality AU files exist but are rare. The format supported quality, but usage patterns favored voice recording and system sounds over music.
When converting: Check source AU specifications first with `ffmpeg -i file.au` or audio editor. This tells you if you have telephony-quality 8kHz audio or higher-quality PCM. Adjust conversion strategy accordingly - low-quality source converts to compressed format, high-quality source deserves uncompressed or lossless target.
Can AU files have metadata or tags?
Not really. AU format has minimal header with technical information (encoding, sample rate, channels) but no standardized metadata for artist, title, album, etc. The header includes optional 'info' field for text description, but this isn't structured metadata - just free-form text that most software ignores.
This is another reason AU is obsolete: modern audio files need metadata for library organization. WAV has INFO chunks, FLAC has Vorbis Comments, MP3 has ID3 tags. AU has effectively nothing. For organized music collection, AU is terrible choice.
When converting: Metadata doesn't transfer from AU (because it doesn't exist). You'll need to add tags manually after conversion using mp3tag, MusicBee, foobar2000, or other tagging software. This is tedious but necessary for proper library management.
Is AU format still used anywhere professionally?
Legacy telephony: Some old PBX (private branch exchange) systems, IVR (interactive voice response) platforms, and telecom equipment still use AU format for voice prompts and recordings. These systems date from 1980s-90s when AU was standard telephony format. Modern systems use other formats, but legacy equipment persists.
Unix purists: Some old-school Unix users maintain AU for historical or philosophical reasons (using same format as Sun workstations). This is nostalgia, not practical necessity. Modern Unix/Linux users prefer WAV, FLAC, or Opus.
Practical answer: No, AU isn't used professionally for new projects. Any new audio work uses WAV, FLAC, AAC, MP3, or Opus. AU exists only in legacy systems that haven't been updated. If starting new project, never choose AU - it offers zero advantages over modern alternatives.
How do I identify AU file encoding type?
FFmpeg probe: Run `ffmpeg -i file.au` in terminal. Output shows encoding (pcm_s16be for 16-bit PCM, pcm_mulaw for μ-law, pcm_alaw for A-law), sample rate, channels, duration. This is most reliable method.
Audio editors: Open AU in Audacity or other editor. File information shows format details. Waveform visualization also hints at quality - jagged low-resolution waveform suggests μ-law/A-law or low bit depth, smooth waveform suggests PCM.
Why it matters: μ-law/A-law AU files are already degraded telephony audio - convert to compressed format (MP3 64-96kbps is plenty). PCM AU files are high-quality - convert to WAV losslessly or FLAC for compression. Knowing encoding prevents inappropriate conversions (like creating 320kbps MP3 from 8kHz μ-law source - waste of space).
AU vs WAV vs AIFF - which format for archival?
Use WAV: Universal uncompressed format, excellent software support, clear specifications, works on all platforms. WAV is the safe, practical choice for uncompressed audio archival. Maximum compatibility, no surprises. Industry standard for uncompressed audio.
Use FLAC: If storage space matters, FLAC provides lossless compression (50-60% of WAV size) with perfect quality. Better long-term choice than uncompressed formats - same quality, less space, excellent software support. Open-source with institutional backing (Xiph.Org).
Don't use AU or AIFF: Both are legacy platform-specific formats (Unix and Mac respectively) with worse compatibility than WAV. AIFF is better than AU (more features, better support) but still inferior to WAV for archival. For modern audio archival: FLAC first choice (lossless compression), WAV second choice (uncompressed standard), AU/AIFF never (obsolete platform formats). Convert existing AU/AIFF to FLAC or WAV for future-proofing.