SND to AMR Converter

SND is a multi-platform audio file extension used across several computing ecosystems since the late 1980s. On Sun and NeXT workstations, .snd files follow the AU format structure — a header with magic number 0x2e736e64, data offset, encoding type, sample rate, and channel count, followed by raw audio. On MS-DOS PCs, the same .snd extension was used by early sound utilities like Sounder and SoundTool for simple 8-bit unsigned PCM recordings. Macintosh systems also employed .snd for sound resources embedded in the resource fork. Because the extension is shared across incompatible formats, audio processing tools typically inspect the file header to determine which variant they are handling: files beginning with the AU magic number are treated as Sun/NeXT audio, while headerless files are interpreted as raw PCM with assumed parameters. The Sun/NeXT variant supports multiple encodings including mu-law, A-law, 8-bit and 16-bit linear PCM, and ADPCM, making it versatile for both speech and general audio. One advantage of the AU-style SND is its self-describing header, which enables any compliant player to determine sample format and rate without external metadata. The MS-DOS SND variants hold historical value as artifacts of the era when Sound Blaster cards first brought digital audio to personal computers. SND files from all platforms can be processed and converted using SoX and other audio tools.

AMR (Adaptive Multi-Rate) is a compressed audio format optimized for speech, standardized by the European Telecommunications Standards Institute and adopted as a mandatory codec for GSM and 3G mobile networks. The codec dynamically switches between eight bit rates — from 4.75 to 12.2 kbps — depending on network conditions and background noise levels. When link quality drops, the encoder shifts to a lower rate, trading marginal clarity for transmission reliability. This adaptive mechanism is defined by the 3GPP specifications and represents one of the most widely deployed voice codecs globally, used in billions of mobile calls. The primary advantage is compression efficiency: one minute of AMR audio at 12.2 kbps occupies roughly 90 KB, practical for voice memos, voicemail, and MMS on bandwidth-constrained networks. Another benefit is built-in voice activity detection and comfort noise generation, reducing transmission during silence. While AMR is unsuitable for music due to its narrow bandwidth (300-3400 Hz), it excels at delivering intelligible speech under challenging network conditions.