About AMR Files
AMR Audio
AMR (Adaptive Multi-Rate) is an audio format optimized for speech, used in phone calls.
Family
Audio Files
Extension
.amr
MIME Type
audio/amr
Can Use As
41 4D 52 46 00 01 00 00 4B 41 49 4A
ASCII: AMRF....KAIJ
📈 Target Minimum File Size (Guaranteed ≥ KB)
Lossless JPEG Q100 + standard COM segment padding for government & exam portals
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HOW AMR CAME TO BE.
AMR — Adaptive Multi-Rate — was standardized by 3GPP in 1999 as the voice codec for 3G mobile networks (UMTS). Before AMR, GSM used a fixed 13 kbps codec that sounded awful but saved bandwidth. AMR’s trick was adaptive bitrate: when signal was strong, the phone would encode voice at 12.2 kbps; as conditions degraded, it would drop to 4.75 kbps, sacrificing audio to keep the call connected.
For 15 years almost every cellphone call in the world used AMR. Multimedia messages (MMS) and voicemail recordings also stored their audio as .amr files. The format is still active in 2G/3G networks and legacy voicemail systems but has been superseded in LTE/VoLTE by AMR-WB and Enhanced Voice Services (EVS). A .amr file is almost always a recorded voicemail or an old phone memo.
Technical Specifications
- MIME type
- audio/amr
- Extensions
- .amr, .3ga
- Standard
- 3GPP TS 26.071 (narrowband), TS 26.171 (wideband)
- Sample rate
- 8 kHz (AMR-NB); 16 kHz (AMR-WB)
- Bitrates
- 4.75, 5.15, 5.9, 6.7, 7.4, 7.95, 10.2, 12.2 kbps
Typical Sizes & Weights
1-min voice memo
45-90 KB
1-hour voicemail archive
3-5 MB
STRENGTHS & LIMITATIONS.
Strengths
- Extremely low bitrate — 4.75-12.2 kbps for speech.
- Designed for error-prone mobile channels — handles packet loss gracefully.
- Tiny file sizes — hours of voice in a few MB.
- Mandatory codec in all 3G/UMTS phones — universal cellular compatibility.
Limitations
- Speech-only — music sounds distorted.
- Narrowband (8 kHz sample rate) — muffled compared to modern codecs.
- Patent-encumbered until recently — licensing fees slowed adoption outside telephony.
- Being phased out of new devices in favor of EVS and Opus.
- Non-standard extensions and variants make tooling inconsistent.
CURIOSITIES & TRIVIA.
Almost every 3G cellphone call between 2000 and 2015 used AMR as the voice codec — billions of calls per day.
AMR can switch between 8 bitrates (4.75 to 12.2 kbps) on the fly as cell signal fluctuates.
The 3GPP extended AMR to AMR-WB (wideband) in 2001, adopted by most LTE/VoLTE networks.
Android phones recorded voice memos as .amr files by default until around 2014.
Despite its limited bandwidth, AMR sounds clear enough for speech — the codec is speech-optimized, not music-capable.
Specialized Utilities for .AMR Files
MP3 Audio Compressor — Reduce MP3 File Size
Compress MP3, WAV, M4A, and FLAC audio files by adjusting bitrate (64k, 96k, 128k, 192k), sample rate, and mono/stereo channels.
Online Audio Cutter & Trimmer
Trim MP3, WAV, FLAC, M4A, and OGG audio tracks to exact start and end timestamps with built-in browser playback and custom bitrate.
Extract Audio from Video
Extract the audio track from any video file and save it as MP3, WAV, or other audio formats. Perfect for creating podcasts, music rips, or voice-only recordings.
Video to MP3 Audio Extractor
Extract high-bitrate MP3 audio tracks from MP4, MOV, MKV, AVI, and WebM video recordings in seconds—ideal for podcasts, lectures, and interviews.
CONVERT FROM AMR
Common Use Cases
Voice recordings, phone calls
Related Formats
Popular comparisons
AMR vs MP3
Differences, file size, and when to choose each format.
AMR vs WAV
Differences, file size, and when to choose each format.
AMR vs FLAC
Differences, file size, and when to choose each format.
AMR vs AAC
Differences, file size, and when to choose each format.
AMR vs M4A
Differences, file size, and when to choose each format.
AMR vs OGG
Differences, file size, and when to choose each format.
Popular AMR conversions
The most-requested destinations when starting from AMR.
Frequently Asked Questions
AMR (AMR Audio) is an audio file format used to store sound recordings — music, voice, podcasts, sound effects. The format defines how the audio samples are compressed (or stored raw), what bitrates are supported, and how metadata such as title, artist, album, and cover art is embedded. It is part of the audio files family.
VLC, foobar2000, and the default media players on Windows and macOS handle AMR natively. On mobile, iOS Music and Android media apps vary in their support — popular formats work everywhere; niche ones may need a dedicated app. If playback fails on a device, converting to MP3 or AAC usually solves it.
Upload the AMR to KaijuConverter and pick MP3, WAV, FLAC, AAC, OGG, or any other target. Our FFmpeg pipeline decodes the audio and re-encodes to the target format at sensible default bitrates (VBR ~190 kbps for music, 96 kbps for speech). Metadata and cover art travel with the audio where both formats support them.
AMR can be lossy or lossless depending on the specific variant. Lossy variants (smaller files) discard some audio detail during compression in ways tuned to be inaudible; lossless variants preserve every sample exactly but produce larger files. For distribution, lossy at high bitrate is standard; for archival, lossless wins.
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