ANSI SCTE 230-2016 pdf free download.Recommended Practice for Proper Handling of Audio- Video Synchronization in Cable Systems
1.1. Executive Summary
It has historically been a ‘given’ that television content is comprised of moving pictures and sound – and that the pictures and sound are presented in synchrony in the viewing / listening environment. Complex signal processing, distribution environments and consumer equipment have all conspired to make the synchronous presentation of pictures and the accompanying sound to a consumer a challenging task.
This document describes the nature of video and audio synchrony, how to recognize and measure the loss of synchrony, and potential identification and remediation steps when that synchrony is lost.
1.2. Scope
This Recommended Practice specifies proper procedures for the measurement of and maintenance of
Audio-Video Synchronization (commonly known as “Lip Sync”) through various aspects of a cable
system – including the headend and distribution architecture and devices.
1.3. Benefits
This document assists the reader with recognition of the issue and where Lip Sync problems may have occurred and how to troubleshoot / mitigate those sync issues. Understanding the issues as outlined in this document will shorten the troubleshooting process and help to increase the ability of technical staff to communicate the issue to consumers as well as maintenance personnel.
1.4. Intended Audience
This document is intended for technical operations engineering and, potentially, customer contact
personnel such as installers to be able to identify audio/video synchronization problems.
2. Informative References
All documents are subject to revision; and while parties to any agreement based on this document are encouraged to investigate the possibility of applying the most recent editions of the documents listed below.
3. Compliance Notation
shall This word or the adjective “required” means that the item is an absolute requirement of this document. shall not This phrase means that the item is an absolute prohibition of this document. forbidden This word means the value specified shall never be used. should This word or the adjective “recommended” means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications should be understood and the case carefully weighted before choosing a different course. should not This phrase means that there may exist valid reasons in particular circumstances when the listed behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label. may This word or the adjective “optional” means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it enhances the product, for example; another vendor may omit the same item. deprecated Use is permissible for legacy purposes only. Deprecated features may be removed from future versions of this document. Implementations should avoid use of deprecated features.
5. Audio Video Synchronization Background and Detection
5.1. Detection and Visibility
Today’s complex ‘source to sink’ flow of digital audio and video includes many active processing steps that may result in undesired changes to the relative timing of video to the related audio. This relationship is commonly called “Lip Sync” – and it is annoying to viewers when the difference in synchronization is great. Lip Sync errors have occurred since motion pictures had sound (including phonograph records accompanying a film evolving through sound-on-film projector loops to a separate sound head). Concerns about Lip Sync errors have remained through analog television to the digital transition and codecs and transport systems. In fact, the ‘transition’ to digital displays has made Lip Sync errors potentially worse. The video input-to- picture output to the viewer delay (“Latency”) was very straightforward with CRT displays, however, contemporary fixed-panel display designs almost-always contain frame-buffers, frame-rate conversion, temporal noise reduction and other signal processing that can introduce significant Latency, including variations in the Latency that are not consistent nor known to external audio equipment. Existing standards (ITU BT.1359) [3] were made with standard definition CRTs not HD fixed-panel displays. No update has been done to the existing ITU standard since the introduction of these new displays.
