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Audio over HDMI

The Blu-ray and HD DVD standards brought two advantages: high resolution (up to 1920x1200) and high-quality audio (Dolby Digital True HD, DTS HD Master Audio, LPCM – Linear Pulse Code Modulation). These factors are going to eventually entice customers to buy movies in the new formats instead of DVD.

There are no limitations regarding video. All graphics cards with HDCP support can play protected Blu-ray/HD DVD movies at 1920x1080, but things are more complicated with respect to high-quality protected audio.

From a technical point of view, there is no obstacle to decoding the various lossless audio formats (DD TrueHD, DTS HD MA, etc) inside the PC and outputting them to the playback device via HDMI or simple analog connections. However, the output interfaces must ensure enough bandwidth, which may be a problem. Besides, no graphics card with HDMI support can output a protected audio track for further decryption and distribution among the audio channels by the hardware receiver because there is no protected audio path.

One way to solve this problem is to output an LPCM audio stream, which requires high bandwidth but no protection. Many studios include LPCM tracks into their Blu-ray releases, but the audio core must have specific functionality to be able to output such tracks to a receiver via HDMI. But if your configuration meets all the requirements, you will enjoy the best audio possible which will be distributed among the channels by your hardware receiver/amplifier.

An audio card capable of outputting audio over HDMI with support for a protected audio path may be another way to solve the problem.

A third method – which is the most obvious one for undemanding users – is to connect the audio equipment directly to the PC. This makes the option of outputting audio via the graphics card’s HDMI port a critical feature for most customers.

Today, the most advanced implementation of the audio-over-HDMI feature is available with ATI Radeon HD 4800/4600/4500 series cards. The integrated audio core from Realtek can output 7.1 audio (192kHz/24bits per sample) with a bit rate of 6.144Mbps in AC3, DTS, Dolby True HD, DTS HD and LPCM formats. Nvidia’s GeForce 8, 9 and GTX 200 series are limited by the capabilities of the S/PDIF interface and support 5.1 Dolby Digital, 5.1 DTS, and 2-channel LPCM. The integrated graphics cores Intel GMA 4500 and GeForce 8300 can output 7.1 LPCM audio, too.

Clearly, most HTPC users do not need an expensive receiver. Moreover, the majority of home cinema lovers do not have audio equipment capable of delivering the advantages of highest-quality audio tracks. They often use an analog connection between their sound card and the speaker system.

Considering the current state of the market, we’d recommend you to purchase a discrete sound card that has a HDMI output and supports as many standards as possible or install a Radeon HD 4000 series graphics card. But if you are not fastidious about the quality of audio, you should base your choice of the audio subsystem on your own preferences and resources.

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