AC-4 IMS (Immersive Stereo) is a compact delivery mode of Dolby AC-4 that packs an immersive, Atmos-style experience into a low-bitrate stream suitable for broadcast and streaming, even down to mobile-friendly rates. Where E-AC-3 carries Atmos via Joint Object Coding on top of a 5.1 core, AC-4 IMS uses AC-4's more modern, more efficient object-based coding to deliver immersive height and placement at a fraction of the bandwidth, rendered to whatever speakers or headphones the listener has. It is part of the next-generation audio toolkit adopted by ATSC 3.0 and DVB. For services balancing immersive ambition against tight bitrate budgets, AC-4 IMS is the efficient path to Atmos.
The book · Volume 5 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From Jitter Buffers and Lip Sync to Atmos, Quality Metrics, and Neural Codecs
AC-4 IMS brings an Atmos-style experience to headphones and phones at low bitrates, so it decides whether immersive audio reaches mobile viewers at all. Volume 5 covers spatial audio and Atmos in detail, with neural codecs, quality metrics such as POLQA and ViSQOL, and synchronization, so you can plan AC-4 IMS next to E-AC-3 Atmos delivery. Written by Nikolay Sapunov, CEO at Fora Soft.
Planning immersive audio for mobile viewers and weighing AC-4 IMS against E-AC-3 Atmos?
We will map AC-4 IMS and Atmos support across your devices and send an immersive audio delivery plan with bitrates and fallbacks. 250+ video products shipped since 2005.
