Does the apple tv pass through digital stereo signal or decode within unit

Discussion in 'Apple TV and Home Theater' started by karllutz, Nov 30, 2008.

  1. karllutz macrumors newbie

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    Nov 30, 2008
    #1
    Hi there,
    I am trying to find a solution to play digital lossless files through my hifi system using the purest digital signal available. I can play directly through my receiver via usb to my computer but the GUI interface is terrible. I was hoping the apple tv could be the solution. When playing stereo music through the apple tv hooked to my receiver does the apple tv pass the signal to my reveiver to decode or does the apple tv use its own dac to decode first?
    Thanks for your help,
     
  2. Michael CM1 macrumors 603

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    Feb 4, 2008
    #2
    You went a little past me on the lingo, but I think what I want to say is the AppleTV does *not* decode the audio itself. I think. In other words, you need the A/V system that decodes Dolby Digital or whatever to get that audio. You just need the digital audio cable (I think ATV uses optical) or the HDMI cable to use for your sound -- whichever kind you can use with your sound system.

    FYI "digital stereo" is kinda confusing since there is no such thing. I think you're calling the sound system a stereo, but that's so 1985! :)
     
  3. karllutz thread starter macrumors newbie

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    Nov 30, 2008
    #3
    Thanks for your help

    Hey, thanks for the help. Yeah, what I meant by stereo was actually two channel sound.......playing music through two speakers. What I want to do is pass through the best signal possible to my reciever in a wav format and then be able to play that music using an IPOD touch as a remote....without cranking up the HDTV.
    I kept finding info about the surround capabilities of the ATV but nothing on just two channel sound. I believe the only way to pass through the digital signal on an ipod using a dock is with the Wadia transport; but then I would be stuck viewing the bad menu system from my receiver on my HDTV. If the Apple TV also passes that signal without being decoded first then I think it's a perfect solution. Thanks again.......
     
  4. Lebowski macrumors 6502

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    Oct 10, 2005
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    Phoenix, AZ
    #4
    I have my aTV connected via HDMI to my LCD TV, and use the optical out to my reciever. That way I can view all content on the TV, but if I want just music I dont have to have the TV on (and use the iPhone to remote).

    aTV will do audio out via HDMI, Optical or Stereo RCA connections. Not sure if there are any restrictions on bit rate and whatnot for audio files. I assume if iTunes can play the audio files, it should be fine on the aTV.
     
  5. Killyp macrumors 68040

    Killyp

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    Jun 14, 2006
    #5
    Digital Stereo does exist, it's what you get out of the TOSLink or Coax output on a CD/DVD Player/AirPort Express/Mac/Apple TV etc...

    The Apple TV is bit perfect I believe, but don't assume you will instantly get a jump in sound quality if you just connect it digitally. All you're doing then is using the DACs in your receiver rather than the DACs in the Apple TV.

    Make sure you disable the iTunes EQ & volume control btw.
     
  6. spacepower7 macrumors 68000

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    May 6, 2004
    #6
    From my understanding, when using iTunes to send music via Airtunes, iTunes/Mac/PC converts the signal to a 16 bit PCM (CD standard) signal that the Airport Express or AppleTV can then send out digitally to a receiver via optical, hmdi (only on the AppleTV), or convert to analog. If you have a decent receiver, then it probably has better digital to analog converters than the AppleTV. In this case, connect the optical out of the AppleTV to your receiver.
     
  7. Duffinator macrumors 6502

    Duffinator

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    Sep 3, 2007
    Location:
    130 miles NE of Cupertino
    #7
    As mentioned the ATV will pass bit perfect audio streams and I use mine in my HT with good results. I'm now looking to get another ATV for use in a dedicated stereo system and my goal is to have better quality sound from the ATV and external DAC than my current Denon DVD-2900 using the analog audio outs. I've been looking at the new Cambridge Audio DACMagic which can be purchsaed for $400. I'm going to initially use my Touch as remote/screen but may add a 22" lcd panel for viewing and use a universal remote like I use in my HT. I'm going to rerip my CD collection using EAC then into ALAC.

    The Wadi iTransport does look interesting but the ATV is less expensive and much more flexible. If anyone knows of a dock like the Wadia that extracts the digital signal before the internal DAC please post a link.
     
  8. Michael CM1 macrumors 603

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    Feb 4, 2008
    #8
    Wait a tick. I thought the digital output on Macs through that funky cable was 5.1 audio (not 2-channel). Or are you saying that it's one of numerous sound outputs available on the digital out? Shoot, this even confuses me.
     
  9. spacepower7 macrumors 68000

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    May 6, 2004
    #9
    The digital out on Mac can pass either a 5.1 or 2 channel signal. It depends on the source signal. Stereo music in iTunes will go out 2 channel, but movies can send out 5.1 AC3/Dolbly Digital. The cable can carry either signal.
     
  10. Michael CM1 macrumors 603

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    Feb 4, 2008
    #10
    OK, good good. For a second I thought Apple had hyped some worthless digital out feature that couldn't support 5.1. I just assumed that it would do stereo as well since I think it was my PS2 that had an optical out but wouldn't do Dolby Digital on some stuff.
     
  11. karllutz thread starter macrumors newbie

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    Nov 30, 2008
    #11
    I think I have my answer; tell me if I am wrong about this....

    I purchased the Apple TV hoping it would pass through the digital signal without processing internally and then allow my receiver to process the signal and play the file. Based on my testing it appears the apple tv does not send the digital signal to the receiver without first being processed internally through it's own DAC....just like an IPOD connected to a receiver.

    My receiver will play .wav, FLAC, etc files directly through a USB port; the files are processed in the receiver and then played through the speakers. However, the reciever will not play Apple Lossless files.

    So...I ripped a cd through Itunes as a .wav file and has an Apple Lossless file and sync'd it with the Apple TV. I then was able to play both the .WAV and the Apple Lossless files through the receiver......so, I guess this means the Apple Tv is decoding the digital file first and then just sending it to the receiver to be played through the speakers.
     
  12. akm3 macrumors 68020

    Joined:
    Nov 15, 2007
    #12
    I assume you have to have processing first in the AppleTV (above, like an iPod) because for protected files, it has to do it's DRM work on it before it is in a format that could be played properly.

    I'm making stuff up out of my butt, but that sounds reasonable to me.
     
  13. keeper macrumors regular

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    Apr 23, 2008
    #13
    I use a TOSlink splitter, one side into my receiver for 5.1 films, the other goes into a beresford DAC into my hi-fi amp for stereo music......
     
  14. Duffinator macrumors 6502

    Duffinator

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    Sep 3, 2007
    Location:
    130 miles NE of Cupertino
    #14
    I think you're wrong but I also don't think you are looking at this correctly. It's one thing to process a format into PCM but it's completely different to take the PCM and output an analog signal from the DAC. There are not 5.1 DAC's in the ATV. If there were it would have 5.1 analog outputs. It does have stereo DAC's evidenced by the stereo analog outputs but using the optical output bypasses the all internal DAC's. So it does process into PCM, most devices do, but it does not use the internal DAC's with the optical output.
     
  15. theBB macrumors 68020

    theBB

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    Jan 3, 2006
    #15
    I am getting confused about what you mean by "processing internally", "through DACs" etc. If you connect AppleTV to your receiver through the optical TOSlink cable, there is not much of an internal processing other than converting AAC, MP3 or Apple Lossless to PCM. Everything is still digital and this decoding is fairly straightforward, so the "quality" of the equipment should not make any difference unless there is a bug in the software. Your receiver will take this PCM signal, just like it would receive from a CD decoder, and convert to an analog signal using its supposedly better DACs before sending them to the speakers. I think this is what you want, isn't it?
     
  16. VideoFreek macrumors 6502

    VideoFreek

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    May 12, 2007
    Location:
    Philly
    #16
    Close, but not quite. When streaming via Airtunes, the file is transcoded to Apple Lossless on the source computer, regardless of the starting format, and then sent to the Airport Express/ AppleTV. This is done presumably to save bandwidth (vs. sending a 16-bit PCM signal). Transcoding to 16-bit PCM occurs in the AE or ATV, and this can then be passed to a receiver via the optical or HDMI output.

    The onboard DAC in the ATV is relevant only if you're using the analog (RCA) outputs. What is happening in your case is that your .wav and Apple Lossless files are being transcoded to 16-bit PCM as outlined above. Essentially what this means is that if you rip a CD in Apple Lossless (or .wav), you will get bit-perfect output via the optical output, as long as you disable any equalization or other sound-distorting "features." (Bit-perfect means that the 16-bit PCM bitstream out of the ATV will be identical to what is on the original CD).
     

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