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What is SPX?

Speex, open-source speech codec for VoIP and voice — stored as audio/speex — uses lossy encoding to handle voip telephony, voice chat, speech compression. Typical file sizes: varies by content.

What is AU?

Sun AU is the native audio format for Sun Microsystems workstations, using simple mu-law encoding or uncompressed PCM.

When Should You Use SPX vs AU?

Use SPX When...

SPX is built for voip telephony, voice chat, speech compression. Think of it as the practical workhorse — small files, big compatibility, no fuss.

Use AU When...

For legacy unix audio, sun workstation sound, nothing beats AU. It sets the standard for quality, trusted by professionals who cannot afford compromises.

SPX vs AU: Key Differences

  • •SPX and AU diverge on compression: lossy compression for the source, lossless compression for the target.
  • •Moving from SPX (lossless) to AU (lossless) means the output file will be larger — but every bit of the original is preserved.
  • •Transparency: N/A
  • •AU files tend to be differently sized than SPX
  • •SPX is optimized for voip telephony, voice chat, speech compression while AU is designed for legacy unix audio, sun workstation sound — choose based on your specific workflow needs

Advantages of SPX

  • ✓SPX compresses data using lossy methods, keeping file sizes manageable for VoIP telephony, voice chat, speech compression.
  • ✓Industry-wide support means SPX files open anywhere — from legacy systems to the latest devices.
  • ✓Small file sizes make SPX ideal for email, web uploads, and cloud storage.
  • ✓From professional software to open-source alternatives, SPX works out of the box.

Advantages of AU

  • ✓AU uses lossless compression tailored for Legacy Unix audio, Sun workstation sound.
  • ✓AU is supported natively on virtually every device, browser, and operating system.
  • ✓AU files are bit-for-bit perfect, preserving every pixel and sample for professional work.
  • ✓AU integrates seamlessly with all major creative tools and workflows.

Common Use Cases for SPX to AU Conversion

  • Radio commercials
  • Guided meditation recordings
  • Audiovisual installation
  • Music education
  • Conference call recordings
  • Field recording preservation

Industry Applications

Audiobook PublishingMusic StreamingLive SoundForensic AudioMedical TranscriptionRadio Broadcasting

Best Practices for SPX to AU Conversion

  • →For SPX to AU: match the sample rate and bit depth to your delivery platform — 44.1 kHz / 16-bit is the standard for music
  • →Apply loudness normalization (LUFS) before conversion to ensure consistent volume across your audio library
  • →AU prioritizes quality — ensure your storage can accommodate the resulting file sizes
  • →Check that metadata tags (artist, album, track number) survive the conversion
  • →Convert a short segment first to verify quality at your chosen bitrate
  • →Keep a lossless master copy in case you need to re-encode for a different platform

Related Article

Video Compression Guide: Reduce File Size Without Losing Quality

Learn more about SPX and AU formats in our detailed guide.

Troubleshooting SPX to AU Conversion

  • !AU audio quality degraded vs SPX → use a higher bitrate (at least 256 kbps for music)
  • !AU file won't play on your device → check format compatibility with your player or platform
  • !Metadata (artist, album, title) lost after SPX to AU conversion → some formats like AU may not support ID3 tags
  • !Volume changed after converting SPX to AU → normalize audio levels before conversion for consistent playback

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About SPX and AU

SPX

SPX (SPX) - Speex, open-source speech codec for VoIP and voice. Best for voip telephony, voice chat, speech compression.

AU

AU (AU audio) - Sun AU, legacy Unix audio format for Sun workstations. Ideal for legacy unix audio, sun workstation sound.

Format Comparison

CompressionLossy → Lossless
TransparencySupported
Use CaseConvert from voip telephony, voice chat, speech compression to legacy unix audio, sun workstation sound
File Size~Small to medium, similar to WAV after conversion

FAQs

Is converting SPX to AU free?

Yes, GoConvertFile offers free conversion of SPX to AU for files up to 100MB. No registration required.

How long does it take to convert SPX to AU?

Most SPX to AU conversions complete within seconds for standard-sized files. Larger files may take longer depending on the conversion complexity.

What is AU best used for?

AU is ideal for legacy unix audio, sun workstation sound. Sun AU, legacy Unix audio format for Sun workstations

Does converting SPX to AU lose quality?

No, converting SPX to AU does not cause additional quality loss — AU uses lossless compression. However, any artifacts already present in the original SPX file will persist in the AU output.

What file size should I expect after converting SPX to AU?

AU files are typically 2-5x larger than equivalent SPX files because AU preserves all pixel data. This is expected and necessary for lossless quality.

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