Digital vs. Analog Audio Output
#1
I don't know how this works, but when I set my audio output to "Digital" for movies I hear a background static hissing noise on my AppleTV with XBMC. When set to digital the audio level seems to be higher and clearer (except for this static noise), when I set it to Analog, the static goes away, but the sound is kinda less clear.

Again, I may just don't understand how this is supposed to work :-)
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#2
The digital output option is for use when you connect your Apple TV to an AV receiver using the S/PDIF optical output of the ATV. Typically this is for surround from DVDs (audio tracks in Dolby Digital Surround or DTS) but it can also be used for stereo.

The hiss that you head from the analog output (or from your TV if fed using HDMI) is due to the fact that the same digitally encoded stream that contains all the surround channels (DD or DTS) gets fed through to the the analog output and also to the TV over HDMI. Because it is encoded it does just sound like hiss if you don't have an AV receiver to decode it.

So if you use an AV receiver with a digital S/PDIF input you can ignore the analog outputs of the ATV and if feeding the TV with video using HDMI then you should turn down the volume on the TV to zero. Modern AV receivers are generally able to take an HDMI input instead of the S/PDIF signal, and I believe they would then strip off the audio before passing the video on to the TV.

If you don't have, or if you are not using an AV receiver, then you should not select the digital output option when playing material with Dolby Digital or DTS encoding.

Does that help to explain it?
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#3
S80_UK Wrote:The digital output option is for use when you connect your Apple TV to an AV receiver using the S/PDIF optical output of the ATV. Typically this is for surround from DVDs (audio tracks in Dolby Digital Surround or DTS) but it can also be used for stereo.

The hiss that you head from the analog output (or from your TV if fed using HDMI) is due to the fact that the same digitally encoded stream that contains all the surround channels (DD or DTS) gets fed through to the the analog output and also to the TV over HDMI. Because it is encoded it does just sound like hiss if you don't have an AV receiver to decode it.

So if you use an AV receiver with a digital S/PDIF input you can ignore the analog outputs of the ATV and if feeding the TV with video using HDMI then you should turn down the volume on the TV to zero. Modern AV receivers are generally able to take an HDMI input instead of the S/PDIF signal, and I believe they would then strip off the audio before passing the video on to the TV.

If you don't have, or if you are not using an AV receiver, then you should not select the digital output option when playing material with Dolby Digital or DTS encoding.

Does that help to explain it?
It helps thanks!
My ATV is connected to an AV receiver (unfortunately, this particular model cannot strip the audio from the hdmi: http://www.us.onkyo.com/model.cfm?m=HT-S...ystems&p=f) via HDMI + S/Pdif. The Av receiver is connected to the TV via HDMI. I'm pretty sure the volume on the TV is muted when I hear the hiss (but need to double check). So, while it helps, I'm not sure what's causing this...
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#4
Turns out I was mistaking and even at volume 1/100 on my TV produced an audible hisse... I zeroed the volume and got rid of the hissing noise. Thanks, S80_UK!
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#5
You're welcome.
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#6
Hi There S80 UK.
Thx for your inputs

Do you have any idea why this static noise with digital audio only happens through XBMC?

I have my ATV connected by optical cable to my AV receiver and HDMI to my TV.
When I play something in my ATV with DD audio my receiver decodes well and no static is presented also on my TV.
If I switch to XBMC(with digital output on) the same file still is decode well by my AV receiver but then I get the static on TV.

Cheers
Julio
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#7
cordeiro Wrote:Do you have any idea why this static noise with digital audio only happens through XBMC?

Sorry - I didn't know that this was an XBMC exclusive. I don't use my Apple TV for anything else. I currently have no knowledge of XBMC inner workings so it would not be helpful for me to speculate as to the reasons for what you have observed.
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#8
Sorry to bump up this thread
My previous setup was HTPC running Linux with HDMI to TV and digital connection to my receiver
Once I switch the output to digital the sound via HDMI to TV was disconnected, so there was no hiss.. with ATV however the sound via HDMI is not disconnected so I have to turn it to 0..
Isn't it possible to duplicate Linux behavior in ATV
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