Coding of fine granular audio signals using High Resolution Envelope Processing (HREP)

High Resolution Envelope Processing (HREP) is a new tool for improved perceptual coding of audio signals that predominantly consist of many dense transient events, such as applause, rain drop sounds, etc. These signals have traditionally been very difficult to code for perceptual audio codecs, particularly at low bit rates. Based on the gain control principle, HREP acts as a pre-/post-processor pair to perceptual audio codecs and preserves the temporal fine structure and subjective quality of applause-like signals. Subjective tests have shown a significant improvement in audio quality of around 12 MUSHRA points by HREP processing at 48 kbps stereo when used together with an MPEG-H 3D Audio codec. The new coding tool has been adopted as part of MPEG-H 3D Audio Second Edition.