AMR (Adaptive Multi-Rate) is an audio compression format specifically optimized for speech coding. It is the standard format used in mobile telecommunications for GSM and UMTS voice calls. AMR focuses on intelligibility rather than high fidelity, allowing for extremely efficient storage of voice recordings like MMS messages and voice memos. Sample AMR files are used to test voice processing and telephony applications. Developers use them to verify that speech recognition engines can accurately process compressed voice data. They are also used to test backward compatibility with legacy mobile messaging systems and to validate the performance of bandwidth-constrained audio streams.