What is SPX?

SPX (audio/speex) uses lossy compression optimized for voip telephony, voice chat, speech compression. Speex, open-source speech codec for VoIP and voice

What is GSM?

GSM 06.10 is a lossy speech codec used in GSM mobile phone networks for compressing voice calls into low bitrates.

When Should You Use SPX vs GSM?

SPX vs GSM: Key Differences

• •The core technical difference: SPX relies on lossy compression whereas GSM uses lossy compression.
• •Both formats share lossy compression, so quality behavior is similar across the two — file size differences come from algorithm efficiency rather than compression philosophy.
• •How transparency is handled: GSM does not support alpha channels — transparent areas in the source will become opaque.
• •File sizes: SPX files typically range N/A and GSM files Very small, 13kbps bitrate.
• •Primary audience: SPX is built for voip telephony, voice chat, speech compression scenarios, while GSM focuses on mobile voice, legacy phone recordings, voicemail — pick the format that matches your output requirement.

Advantages of SPX

• ✓SPX applies lossy compression specifically calibrated for VoIP telephony, voice chat, speech compression.
• ✓SPX enjoys broad native support across operating systems, browsers, and creative tools alike.
• ✓SPX delivers impressive compression ratios, shrinking files dramatically while keeping visual quality high.
• ✓You will find SPX support built into virtually every tool that handles VoIP telephony, voice chat, speech compression — no plugins or converters needed.

Advantages of GSM

• ✓At its core, GSM relies on lossy encoding — a design choice that makes it perfect for Mobile voice, legacy phone recordings, voicemail.
• ✓You won't run into compatibility issues with GSM — it's a universal standard across platforms.
• ✓File size management with GSM: aggressive compression with minimal visible quality loss.
• ✓Every major application in the Mobile voice, legacy phone recordings, voicemail space supports GSM natively.

Common Use Cases for SPX to GSM Conversion

• Podcast distribution
• Voice recordings
• Streaming services
• Audio books
• Sound design
• Language learning

Industry Applications

Best Practices for SPX to GSM Conversion

• →Converting SPX to GSM: GSM uses lossy compression — choose a higher bitrate (320 kbps) for near-CD quality
• →Normalize audio levels before conversion for consistent playback volume
• →GSM excels in professional audio workflows
• →Always keep a backup of your original files before converting
• →Choose the appropriate quality settings for your specific use case

Related Article

Troubleshooting SPX to GSM Conversion

• !Clicks or pops in the converted GSM → sample rate conversion can introduce artifacts; use a clean multiple of the source rate
• !GSM file has silence at the beginning or end → trim the source SPX file before converting to avoid unnecessary padding
• !Stereo image collapsed after converting SPX to GSM → verify that the converter preserves channel mapping for multichannel audio
• !The converted GSM clips or distorts at peaks → reduce the gain or apply a limiter before conversion to prevent hard clipping

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