Measuring HDMI Audio
From its origins in 2002 as a new, smaller connector for HDTV, High-Definition Multimedia Interface (HDMI) evolved continuously over the years to become one of the most widely adopted interfaces. This article provides practical answers on how to perform HDMI audio measurements, dealing with the interface’s multiple options and configurations.
Measuring HDMI Audio
How do you measure HDMI audio? This is a question we often hear as HDMI soundbars become more commonplace and the rapid adoption of surround sound and spatial audio systems with televisions continues. While some manufacturers offer expensive custom interfaces to test HDMI devices, there is a much more cost-effective method. Some software-based audio measurement systems can be used with a $100 off-the-shelf interface that enables test signals to be sent via HDMI to a soundbar or surround sound system for measurement. In this article, we discuss how the HDMI protocol handles audio and demonstrate acoustic measurements on a soundbar using Listen SoundCheck software with a commercially available HDMI audio extractor. This method can be extended to a wide range of HDMI connected devices including multichannel surround sound systems.
HDMI Audio
Modern HDMI systems offer Audio Return Channel (ARC) functionality. This allows a single HDMI connection to be used as both an audio input and an output, providing a two-way flow of audio, in addition to video, between devices. This eliminates the need for a dedicated audio cable to connect a soundbar or AV receiver to the television, simplifying configuration and reducing cost and cabling. ARC supports up to six-channel compressed audio and has a maximum bandwidth of 1Mb/second. It supports various audio formats including PCM (2 channel), Dolby Digital (up to 5.1 channel), and DTS Digital Surround (up to 5.1 channel).
A newer version, Enhanced Audio Return Channel (eARC) improves upon ARC with a significant boost in bandwidth and speed, enabling transmission of higher quality audio from a TV to a soundbar or AV receiver. It carries up to 32-channel audio, including eight channels of 24-bit/192kHz uncompressed audio, and supports modern advanced audio formats such as DTS-HD Master Audio, DTS:X, Dolby TrueHD, and Dolby Atmos.
Many audio devices that are used with audiovisual systems, such as soundbars, speakers, gaming headsets, and so forth, are unable to accept an HDMI input with video directly. A small device called an HDMI extractor is commonly used to split the audio and visual HDMI signals so that the audio signal can be played directly on a soundbar or surround sound system. Audio extractors typically cost around $100 and can be purchased online or from electronics or AV stores.
These widely available devices also enable HDMI audio devices to be measured using a software-based audio analyzer. To measure audio, a test stimulus must be sent from the computer to the device under test (DUT). Although soundbars usually feature an HDMI port, as do most computers, typically the device’s audio channels will not be accessible if they are directly connected via an HDMI cable.
