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Why Do DACs Have a Digital Output?

Al Griffin  |  Apr 9, 2015

Q I read lots about digital to analog audio converters (DACs), mostly because of high-res computer audio. Here’s my question: Why do some DACs have a digital output? If the purpose of a DAC is to convert a digital audio signal to analog, why would you want it to output the signal in digital format as well? —Jacques Simard

A Standalone DACs were initially used to improve the sound of a CD player hooked up via a coaxial or Toslink digital connection. But DACs nowadays serve multiple functions: most include USB ports and can process digital audio sources ranging from computers to media servers to media streamers like the Apple TV.

While a digital output connection on a DAC might seem contrary to its main function, there’s a good reason why you’d want one there. Say you have a Blu-ray player connected to the DAC. When playing a two-channel format such as a CD, the DAC would be used convert the stereo PCM signal coming from the CD to analog. But when playing a movie on Blu-ray or DVD using the same machine, you’d instead want the DAC to kick into pass-through mode and route the multichannel digital bitstream on disc to your AV receiver for processing.

Standalone units ranging from Music Hall’s dac15.2 ($299) and Cambridge Audio’s DacMagic Plus ($599) up to the Benchmark DAC2 HGC ($1,995) are good examples of DACs that provide a digital output. While the main use case for these would be the multichannel soundtrack pass-through cited above, some folks use DACs to derive dual digital/analog output from a source like a media streamer to feed an AV receiver for multiroom audio. Why? Many AV receivers aren’t capable of distributing digital audio signals for zone 2/3 output, so sources like an Apple TV that only provide a digital output require digital-to-analog audio conversion before audio can be routed to additional zones.

COMMENTS
Arnaud32's picture
Submitted by Arnaud32 on April 9, 2015 - 9:34pm

I do have a Marantz SR7005 A/V receiver, and there is a trick to send an audio signal from the apple TV to zone 2/3 (as well as my oppoBD93 player).
The marantz manual clearly states that it is unable to direct HDMI sound signal to a Zone 2/3. In order to overcome the situation, I did connect the Apple TV to the receiver using both an HDMI cable and the optical outpout onto the receiver. Then, In the receiver input options, I activated both my HDMI and the optical as AppleTV Input. Same thing for the Oppo : Dual connection HDMI + optical, activated as the "BD input" on the marantz.
By doing so, I am still able to hear my DTSHD soundtracks on Blu-Rays in my TV room, but also listen to CDs in Zone 2. The only limitation is that Zone 2 can't decode multichanel streams => 5.1SACD won't work on zone 2, unless i set up the oppo as a stereo output for SACD (which, in, for example, "the Dark Side of the Moon", is a pity...)

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