Apple TV 3 Audio Pops

I've been using two Apple TV 2's for quite a while and just purchased an Apple TV 3. I immediately noticed some audio pops that I never heard before on the Apple TV 2. These occur when starting to play video files (but not music): there is an initial pop as the movie is spooling followed by a second louder one just prior to the video starting. Additionally, there is another pop when I leave the movie and go back to the menu. It will go through the same set of pops if I resume from the middle of a movie. I called Apple tech support, and they said it should be replaced, so I did that. The replacement unit behaves identically, so it appears that this is something inherent in the Apple TV 3 that is not in the Apple TV 2. I haven't found any other references to anything like this, so it also appears to be

1. Switched from HDMI audio in to optical in on my receiver (Denon AVR-890), no difference, it still pops.
2. Updated to latest software, no difference.
3. Swap out the Apple TV 3 with an Apple TV 2 using the same cables, there are no pops.
4. Route HDMI directly to TV, optical audio to receiver, there are no pops.

So there appears to be some kind of issue with the HDMI in the Apple TV 3, maybe in combination with my receiver. Number 4 is not a solution I can use because I need to route video through the receiver to get volume info. This is not a great problem, but it is enough of an irritant that I'd like to eliminate it. The questions that I have are a) is there anything else I could try, and b) is this a problem unique to me. Thanks.

waw74 said:

try turning dolby digital off in the aTV menu.

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Wow, you nailed it! Turning off Dolby Digital eliminates the pops. That's what I love about these forums, smart people who are willing to take the time to help people with problems.

So I went back to my Apple TV 2's to see what the settings were, and both had Dolby Digital set to off. That must have been the default, since that's a setting I've never looked at. And the default on Apple TV 3 must be on. So now the question I have is what does is mean to have it Dolby Digital off? It has seemed to me that I've had good 5.1 surround from my Apple TV 2 with it off.

waw74 said:

I have an aTV3 hooked to a Denon avr-1912 via HDMI, I've never noticed any pops.

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OK, now that I've compared some material using Dolby Pro logic II and Dolby Digital I see what I've been missing. So I do want to leave Dolby Digital turned on, but I have these pops. You said you've never noticed any with your Denon receiver. Do you have any idea why I might be getting them also with a Denon receiver?

Stolz25 said:

I'll bet you just had the reciever set to play from all speakers. This isn't really surround sound, I use it when listening to music.

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Well I don't really understand what the Apple TV outputs when Dolby Digital is set to off, but my receiver shows "Pro Logic II". Without making any changes to the receiver, setting Dolby Digital to "on" on the ATV, the receiver shows "Dolby Digital". I guess Pro Logic is some sort of synthesized surround sound.

waw74 said:

you got it, pro logic is dolby's way to put surround into 2 channels.
http://en.wikipedia.org/wiki/Dolby_Pro_Logic

it basically takes sounds that are on both the left and right channels, and if they're in phase puts them to the center channel.and if they're out of phase it puts them to the rear channels.

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Thanks. For some reason I had it in my head that Pro Logic and Dolby Digital were equivalent.

Back to my earlier question, I now have to live with the pops, but do you have any idea of why I get them and you don't?