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    Dolby Audio Support on Apple TV

    November 25, 2015 by Andy Vaughan

    The new Apple TV® comes with support for Dolby Digital Plus™ audio up to 7.1 channels and Dolby® Digital audio up to 5.1 channels, which enables content providers to use Dolby Audio™ to deliver even richer and more immersive experiences to the new Apple TV. The purpose of this article is to help you understand the differences between the possible audio choices and the resulting audio output.

    Decoding Audio Streams

    Apple TV includes a built-in decoder for Dolby Digital Plus and Dolby Digital audio. This means that the Apple TV is able to decode Dolby audio rather than simply pass the compressed bitstream to another device (such as an audio/video receiver [AVR] or a sound bar). Decoding the audio inside of the Apple TV enables Apple to support several features such as mixing of other sounds from the system, Siri® voice input, and so on.

    When a user plays media with stereo or multichannel audio (including Dolby Digital Plus and Dolby Digital audio), the audio soundtrack is decoded to two or more PCM channels (uncompressed digital audio) before it is sent to the AVR or other downstream device.

    It is important to keep in mind that while the Apple TV supports Dolby Digital Plus, this does not mean the Apple TV is necessarily sending a Dolby Digital Plus bitstream over its HDMI® output. After it decodes the Dolby audio, the Apple TV sends the audio to your receiver via HDMI; how it sends the audio depends on the Apple TV settings as well as the capabilities of your HDMI-connected device.

    Apple TV Audio and Video Settings

    In the Apple TV settings, go to the Audio and Video settings, and then into the Surround Sound section. There you will see options for Auto, Dolby Surround and Stereo.

    Which to Choose?

    Here is what each option does:

     

    • Auto – In most cases, Auto is the best setting. It allows the Apple TV to automatically detect the capabilities of the device you are connected to and deliver the appropriate audio stream. If you are connected to a stereo device it will send stereo PCM audio; but if you are connected to a multichannel device, it will send multichannel PCM audio, including 5.1 or 7.1, depending on the capabilities of the connected HDMI device.
    • Dolby Surround – This setting is intended to force the Apple TV to output a Dolby Digital (also known as “AC3”) compressed bitstream. This may be required with certain legacy devices or sound bars that support the older Dolby Digital format but do not yet support Dolby Digital Plus or multichannel PCM audio. Remember that Dolby Digital is only capable of up to 5.1 channels of audio, so this option will never be able to send 7.1 channel audio to the connected HDMI device.
    When this setting is selected, the audio is first decoded (although constrained to 5.1 channels) and mixed with other system sounds, and is then reencoded to the legacy Dolby Digital format just prior to the HDMI output. The connected device (TV, sound bar or AVR) will then receive a Dolby Digital bitstream.
    • Stereo – This setting forces the Apple TV to just send stereo PCM. All audio is decoded on the Apple TV and is downmixed to stereo if necessary.

    To hear 7.1-channel audio from a Dolby Digital Plus soundtrack, you must use the Auto setting.

    Assuming that your AVR is capable of receiving 7.1 channels of audio, and assuming that the content that you are playing includes a 7.1-channel Dolby Digital Plus audio soundtrack, you will then see that your receiver is receiving multichannel PCM audio from the Apple TV, and the receiver should indicate that 7.1 channels are detected. This carries the 7.1-channel audio decoded from the Dolby Digital Plus audio track. The only difference is that it is being sent to your receiver as multichannel PCM audio and not as a Dolby Digital Plus bitstream.

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