HDMI carries both video and audio, making it the backbone of modern home entertainment. Yet audio configuration through HDMI often confuses consumers more than video setup. Terms like ARC, eARC, passthrough, and lossless audio appear in product specifications without clear explanation. This guide demystifies HDMI audio, helping you understand how to achieve the best sound quality from your setup.
How HDMI Audio Works
HDMI can transmit audio in several ways, depending on your equipment configuration. Understanding these audio pathways helps you optimise your setup.
Source to Display
The simplest audio path is from a source device (like a streaming box or gaming console) directly to your television through HDMI. The television receives the audio signal and plays it through its built-in speakers. While convenient, TV speakers typically can't match the quality of external audio systems.
Source to AV Receiver to Display
In traditional home theatre setups, source devices connect to an AV receiver, which processes audio for connected speakers and passes video to the display. This provides the highest audio quality but requires all sources to route through the receiver.
Audio Return Channel
ARC allows your television to send audio back to a connected soundbar or AV receiver. This means the television's built-in apps can output their audio to your sound system without requiring a separate cable. ARC fundamentally changed how people connect soundbars, simplifying setups that previously required optical audio cables.
Understanding ARC (Audio Return Channel)
Introduced with HDMI 1.4, ARC enables bidirectional audio over the same HDMI cable used for video. When you watch Netflix through your television's app, ARC sends that audio to your soundbar or receiver.
ARC Capabilities
Standard ARC supports stereo audio and compressed surround sound formats including Dolby Digital and DTS. For most television watching, this provides adequate quality. However, ARC has bandwidth limitations that prevent transmission of higher-quality audio formats.
ARC Limitations
ARC cannot transmit lossless audio formats like Dolby TrueHD or DTS-HD Master Audio. When these formats are sent through ARC, they're compressed to fit within ARC's bandwidth, losing audio quality. For Dolby Atmos, ARC transmits the lossy Dolby Digital Plus version rather than the full lossless TrueHD Atmos.
Many users don't notice this limitation because streaming services often use compressed audio anyway. However, for Blu-ray playback or when quality matters most, ARC's compression becomes audible on good audio systems.
ARC is typically available on only one HDMI port on your television, usually labelled "ARC" or with an arc symbol. Connect your soundbar or receiver to this specific port for ARC functionality.
Enhanced ARC (eARC)
eARC, introduced with HDMI 2.1, dramatically expands audio return capability. It removes bandwidth restrictions, enabling lossless audio transmission from television apps to your audio system.
eARC Capabilities
eARC supports up to 32 channels of uncompressed audio at high sample rates. This includes full lossless Dolby TrueHD Atmos, DTS-HD Master Audio, and DTS:X. The audio quality from Netflix or Disney+ through eARC matches what you'd get from a Blu-ray player connected directly to an AV receiver.
eARC Requirements
Both your television and audio device must support eARC for it to function. You also need an Ultra High Speed HDMI cable (or at least one rated for eARC bandwidth) for the connection between TV and soundbar or receiver. Using an old High Speed cable limits you to standard ARC capability.
Enable eARC in both your television's settings and your audio device's settings. The terminology varies by manufacturer, with some calling it "eARC" and others using terms like "Enhanced Audio Return."
Audio Format Compatibility
Different audio formats offer varying quality levels and surround configurations. Understanding these helps you configure your system optimally.
Stereo (PCM 2.0)
Two-channel audio works universally and provides excellent quality for music and dialogue-focused content. If surround sound isn't working properly, falling back to stereo ensures you hear something.
Dolby Digital and DTS (5.1)
These compressed surround formats provide discrete audio for front, centre, and surround speakers plus a subwoofer channel. They're widely supported and work through standard ARC. Quality is good for television and streaming content.
Dolby TrueHD and DTS-HD Master Audio
Lossless versions of Dolby and DTS formats, found on Blu-ray discs. These require eARC for transmission from television apps or direct connection from a Blu-ray player to your receiver. Audio quality is noticeably better than compressed versions on capable systems.
Dolby Atmos and DTS:X
Object-based audio formats that add height information for three-dimensional sound. They can be encoded within both compressed (Dolby Digital Plus) and lossless (TrueHD) containers. Streaming services use the compressed version, which works through ARC. Full lossless Atmos requires eARC.
Most AV receivers and soundbars display the active audio format. When playing Atmos content, look for "Atmos" or "TrueHD Atmos" on your audio device. If you see "DD+" instead, Atmos is compressed. This helps verify your configuration is correct.
Connecting Soundbars
Soundbars have become the most popular audio upgrade from television speakers. HDMI provides the best connection method for modern soundbars.
Basic Soundbar Setup
Connect your soundbar's HDMI output to your television's ARC or eARC port. Enable ARC/eARC in both devices' settings. Configure your television to output audio through external speakers rather than its built-in speakers.
Most modern soundbars and televisions support HDMI-CEC, which enables volume control from your television remote. This simplifies operation significantly.
Soundbars with HDMI Inputs
Some soundbars include HDMI inputs for connecting source devices. This allows the soundbar to process audio directly from gaming consoles or Blu-ray players, ensuring maximum compatibility. Video passes through to your television. This configuration avoids ARC bandwidth limitations entirely.
Configuring AV Receivers
AV receivers offer the most flexibility but require more configuration than soundbars.
Traditional Setup
Connect all source devices to your receiver's HDMI inputs. Connect the receiver's main HDMI output to your television. Audio processing happens in the receiver, with video passing through to the display. This provides full audio quality and format support.
Using eARC with Receivers
Alternatively, connect sources directly to your television and use eARC to send audio to your receiver. This approach takes advantage of your television's smart features and input switching while still getting high-quality audio to your receiver. Ensure both TV and receiver support eARC for lossless audio formats.
Troubleshooting Audio Issues
Audio problems through HDMI are common but usually have straightforward solutions.
No Audio to Soundbar or Receiver
Verify you're connected to the ARC-labelled port. Enable ARC/eARC in both devices' settings. Set your television's audio output to "External Speakers" or "ARC." Some televisions automatically switch when detecting a connected audio device, while others require manual configuration.
Surround Sound Not Working
Check your source device's audio output settings. Many default to stereo for maximum compatibility. Set audio output to "Auto" or your desired surround format. Verify your audio device supports the format being transmitted.
Audio Delay
Lip-sync issues where audio doesn't match video often occur with ARC connections. Most receivers and soundbars have audio delay adjustments to compensate. Some televisions also offer "AV Sync" or similar settings.
For the best HDMI audio experience, use eARC if your equipment supports it and connect with an appropriate high-bandwidth cable. Standard ARC works well for television and streaming, but eARC unlocks full lossless audio quality. Verify your specific audio format appears on your receiver or soundbar to confirm proper configuration.
Future Audio Standards
Audio technology continues advancing. MPEG-H 3D Audio and other emerging formats may eventually join Dolby Atmos and DTS:X. eARC's high bandwidth ensures compatibility with future formats without requiring new cables, making it a worthwhile investment for serious audio enthusiasts.
Understanding HDMI audio features empowers you to get the most from your entertainment system. Whether you're using a simple soundbar or a full Dolby Atmos speaker array, proper HDMI audio configuration ensures you hear content as it was meant to be experienced.