Continuously Variable Slope Delta modulation is a voice coding method. It is a delta modulation with variable step size (adaptive delta modulation), first proposed by Greefkes and Riemens in 1970
FLAC is a lossless audio file format. It is similar to MP3 format but the main difference between these 2 formats is FLAC file compress the file size without changing the quality of audio. It can compress an audio file up to half of its original size using lossless compression algorithm.