What is AMR (Adaptive Multi-Rate)?
Complete guide to the AMR file format
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What is AMR (Adaptive Multi-Rate)?
AMR (Adaptive Multi-Rate) is an audio format specifically designed for mobile phone voice recordings. It provides excellent speech compression at very low bit rates (4.75-12.2kbps).
AMR was developed as the standard codec for GSM mobile phone networks and is still widely used for voice memos and recordings on Android phones and WhatsApp voice messages.
How AMR Works
AMR is a speech codec that uses Algebraic Code-Excited Linear Prediction (ACELP), a model tuned for the human voice rather than general audio.[3] The "adaptive multi-rate" name refers to its eight selectable narrowband bit rates between 4.75 and 12.2 kbit/s; an encoder can switch rates frame by frame to balance speech quality against available network bandwidth.[2] Audio is processed in 20-millisecond frames sampled at 8 kHz.[1]
Standardization and Storage
AMR was adopted by 3GPP as a mandatory speech codec for GSM and UMTS mobile networks. IETF RFC 4867 defines both its RTP payload format for real-time transport and the file storage format, which begins with the magic header #!AMR.[1] A wideband variant, AMR-WB, raises the sampling rate to 16 kHz for clearer voice and is covered by the same specification.[1]
Limitations
Because the codec discards frequency content outside the speech band, AMR is poorly suited to music or high-fidelity audio, where it produces noticeably degraded results.[3] Its strength is achieving intelligible voice at bit rates an order of magnitude lower than general-purpose audio codecs.[2]
Technical Details
AMR vs Other Audio Formats
| Feature | AMR | MP3 | Opus |
|---|---|---|---|
| Compression | Lossy[1] | Lossy | Lossy |
| Optimized for | Speech[2] | Music | Speech & music |
| Developer | 3GPP[3] | Fraunhofer / MPEG | Xiph.Org / IETF |
| License | Patented[1] | Patented (now free) | Open, royalty-free |
| Typical use | Mobile voice recording | General music | Modern voice/music |
| Best for | Phone voice memos | General music | Voice over IP |
AMR is tuned for low-bitrate mobile speech, whereas MP3 suits music and Opus covers both at higher efficiency.
Pros and Cons
Advantages
AMR files are extremely small - a 1-minute recording is only 50-90KB.
Excellent quality for voice recordings at extremely low bit rates.
Universal support on Android phones and messaging apps.
Low computational requirements save battery on mobile devices.
Disadvantages
AMR is terrible for music - it is optimized only for human speech frequencies.
AMR cannot be played on most desktop media players without codecs.
Any music recorded in AMR will sound extremely poor.
iPhones use M4A for voice recordings instead of AMR.
When to Use AMR (Adaptive Multi-Rate)
Here are the most common situations where AMR (Adaptive Multi-Rate) is the right choice:
WhatsApp Voice Notes
WhatsApp voice messages are stored as AMR files on Android devices.
Android Voice Memos
Many Android devices save voice memos as AMR files.
Low-Bandwidth Voice
AMR is used in situations where voice must be transmitted over very low bandwidth connections.
Embedded Systems
IoT devices and embedded systems use AMR for voice recording due to low resource requirements.
Convert AMR (Adaptive Multi-Rate) Files
Need to convert your AMR files? Use our free online converter.
Try Audio Converter FreeFrequently Asked Questions about AMR (Adaptive Multi-Rate)
Can I play AMR files on my computer?
VLC media player can play AMR files. Windows Media Player and iTunes do not support AMR by default.
How do I convert AMR to MP3?
Use our free online converter to convert AMR to MP3 for universal playback.
Why did WhatsApp send me an AMR file?
WhatsApp voice messages sent from Android devices use AMR format. Use VLC to play them.
Is AMR good for music?
No, AMR is designed only for voice. It sounds terrible for music due to very low bit rates.
Can iPhone play AMR?
iOS does not natively support AMR. Third-party apps like VLC can play AMR files on iPhone.