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My 4k ATV outputs DD 5.1 at 48 kHz @ 640 bps with iTunes movies. Can it output higher rates?

Audit13

Audit13

macrumors 604
Original poster
Apr 19, 2017
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Toronto, Ontario, Canada
My Apple TV 4k is connected directly to the TV because my receiver doesn't support DV or HDR. I run an optical cable from the TV to the receiver for sound. I can see that my receiver is getting DD 5.1 sound from my purchased iTunes movies at 48 Khz and 640 kbps. I currently have a 5.1 speaker arrangement.

Does the Apple TV 4k support higher audio bit rates? I'm asking because, if it does, I would be willing to change my receiver to a model that supports DV and HDR.

Any information would be appreciated.

Thanks for reading.
 
If you look at the specs

https://www.apple.com/apple-tv/specs/

it supports Dolby Digital Plus 7.1, which can give you a bitrate up to 6144 Kbps.

https://en.wikipedia.org/wiki/Dolby_Digital_Plus

But that is all theoretical.

One of the key things you need to consider is what media are you playing? The audio bitrates for Netflix, Amazon and most stream media sources are abysmal, ranging from about 128 kbps to 256 kbps. On the other hand if you are playing movies from a media server with DTS-MA sound that's something different. I played a DTS-MA track on the Apple TV with Plex and saw a bitrate of 640 Kbps. Infuse sees the DTS-MA track and plays it, but since the developer HUD doesn't work with the Infuse player I could not determine what bitrate was actually being delivered by the Apple TV.
 
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When playing an iTunes 4k movie, my receiver's front panel indicates that it is receiving DD 5.1 at 48 kHz with a bit rate of 640 Kbps. I have not seen my receiver indicate that it is receiving a signal that is less that 48/640 in iTunes movies.

For DTS-HD and TrueHD, I get that from my htpc that has its video connected directly to my TV and audio connected directly to my receiver.

A DTS-HD MA soundtrack at 640 kbps seems a bit low based on my reading of this article: https://www.tomsguide.com/us/high-def-audio-hdmi,review-1088-4.html

If the apple tv 4k can output Dolby Digital Plus, I'll have to get a new receiver: https://www.lifewire.com/digital-optical-connection-1846881
 
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iTunes movies with 5.1 sound usually use DD 5.1 at 384 kbps. The reason you see 640 kbps on your receiver is that the ATV4 transcodes all audio (including UI "swish" sounds etc.) to that format if you set the output to DD (or the ATV detects that you are using optical S/PDIF which doesn't support multichannel-PCM). This transcoding can theoretically reduce the audio quality due to so-called tandem losses (if you can hear a difference given the quality of the source material is another question). If you had an AVR that can accept audio via HDMI you could set the ATV to output sound in uncompressed PCM format, which would remove one lossy compression step and theoretically improve the quality, but I doubt it would matter if you are only using purchased iTunes movies.
 
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It has been discussed at length recently, that one of the main complaints for aTV among the enthusiasts is its lack of audio passthrough.
That means, that aTV 4 and 4K do not output anything except PCM and does decode both supported multichannel formats - DD 5.1 and DD+ 7.1 - internally.
One exception - if you set its Audio output to Dolby Digital 5.1 it will internally re-encode the audio back into AC3
No DTS flavors have been supported so far by Apple (there have been various apps that have tried work around this, lately these workarounds to pass audio bitstream directly to HDMI out have failed again).
https://developer.dolby.com/blog/dolby-audio-support-on-apple-tv/
 
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Audit13 said:
A DTS-HD MA soundtrack at 640 kbps seems a bit low based on my reading of this article:
Click to expand...

Absolutely. It usually runs 1,500 mbps or higher. That 640 kbps is the only rate that I could verify with the Developer HUD streaming to Plex (which uses the apple player). It is possible that I had not selected the right audio track to stream in Plex. I assume that Infuse gives you a much higher rate, but I just can't verify it. Bottom line is that the Apple player cripples audio. Unclear quantitatively the difference running Infuse.

If you are running 5.1 that means that each channel is only ~106 kbps per each of the 6 channel. [I realize that this totally simplistic but I'm just looking for orders of magnitude here].

Until Apple fixes this to get the best quality you need to stream to something like an Oppo DNLA player. Streaming the same file from the Plex server using Oppo's DNLA client the Oppo clear shows that it is a DTS-MA stream.

If you replace your receiver and the replacement has a DNLA client then you could stream from a Media server and if the receiver supports it you could then get full DTS-MA. As for public streaming services I don't know of any that give you anything even near DTS-MA. I have been able to verify that you can get just audio at high quality if you stream from the Tidal app. There may be other audio apps that do this as well.
 
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Audit13 said:
Thank you for the great replies.

Hopefully, I'll be ordering a new receiver this weekend. The problem is that Anthem receivers are so expensive!
Click to expand...
If the ATV is your only reason, I would recommend to wait. It's likely that the ATV will soon get better support for audio bitstreaming in order to implement the announced Dolby Atmos support (in fact it already had limited support for bitstreaming that was e.g. utilized by the Infuse app).
 
Rigby said:
If the ATV is your only reason, I would recommend to wait. It's likely that the ATV will soon get better support for audio bitstreaming in order to implement the announced Dolby Atmos support (in fact it already had limited support for bitstreaming that was e.g. utilized by the Infuse app).
Click to expand...
The atv isn't the only reason for upgrading. My current receiver can't do HDR, DV, Atmos, or 4k at 50/60. I can't get arc over HDMI to work either.
 
Audit13 said:
The atv isn't the only reason for upgrading. My current receiver can't do HDR, DV, Atmos, or 4k at 50/60. I can't get arc over HDMI to work either.
Click to expand...
If you are interested in ARC, it may be a good idea to look for a suitable AVR with eARC support (which can support the full range of audio formats while ARC is limited to basic formats similar as S/PDIF). A few eARC-ready AVRs are already available.
 
Rigby said:
If you are interested in ARC, it may be a good idea to look for a suitable AVR with eARC support (which can support the full range of audio formats while ARC is limited to basic formats similar as S/PDIF). A few eARC-ready AVRs are already available.
Click to expand...
Thanks for the suggestion. I'm interested in an Anthem receiver. Unfortunately, it didn't support eArc. My other option is a marantz sr7012.
 
Audit13 said:
Thanks for the suggestion. I'm interested in an Anthem receiver. Unfortunately, it didn't support eArc. My other option is a marantz sr7012.
Click to expand...
The Marantz will get eARC support with a firmware upgrade. Another option is Denon X4400H or X6400H. I think Pioneer also has a few models. Even though TVs with eARC are still rare, I think this will be a very useful feature in the future (and I typically keep my AVRs for a long time).
 
Audit13 said:
I just checked the bit rate for audio OTA TV and my receiver also says Dolby Digital, 48 Khz, and 640 kbps.
Click to expand...

priitv8 said:
640kbps is the max Dolby Digital 5.1 can go.
Click to expand...

I'm a little confused here. Not sure what "OTA" means. Yes, Dolby Digital 5.1 only goes to 640 kbps, but the Apple TV supports Dolby Digital Plus which can go to 6144 kbps. If the receiver shows 640 kbps it could mean a couple of things:

1. The source material is DD+ or higher but is being provided at 640 kbps
2. The source material is only Dolby Digital
3. The receiver does not support DD+ so it decodes as DD only
4. The receiver does decode DD+ but reports it as DD. This would imply that the source is only 650 kbps

and probably other things as well ....
 
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OTA means over-the-air.

My receiver does support DD+ but maybe all of the iTunes movies I have are only DD. Tried Netflix on the apple 4k and all of the movies are still showing DD.

I'm not too worried because I'll be shopping for a new receiver this weekend.
 
I hooked up the Apple TV to my Marantz receiver via HDMI.

When I select Dolby Digital, the Marantz info screen says its getting 5.1 Dolby Digital.

When I select Best available, the Marantz info screen says it's getting multi-channel PCM but no bit rate. I assume the ATV is decoding the signal before sending it out as multi-channel PCM. Anyone know what the bit-rate range would be for a DD+ signal from an Itunes movies such as Prometheus or Alien Covenant?

Thanks.
 
This may not be helpful as I don't have a 4K Apple TV (I have the previous generation), but playing Independence Day Resurrection 1080p shows an average video bitrate of 7.37 Mbps and 384 kbps audio using "Best Available" audio.

Interestingly enough playing the same movie on Vudu shows 8.05 Mbps video and 192 kbps audio. So iTunes with a 2x higher bitrate for audio would seem to offer better sound.
 
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HDFan said:
This may not be helpful as I don't have a 4K Apple TV (I have the previous generation), but playing Independence Day Resurrection 1080p shows an average video bitrate of 7.37 Mbps and 384 kbps audio using "Best Available" audio.

Interestingly enough playing the same movie on Vudu shows 8.05 Mbps video and 192 kbps audio. So iTunes with a 2x higher bitrate for audio would seem to offer better sound.
Click to expand...
This information is definitely helpful. If I can't get DD+ out of the Apple TV, either as decoded multi-channel pcm or a DD+ stream for decoding by a receiver, I may as well save myself some money until the Apple tv can output more than 640 kbps.

How were you able to determine these bit rates? I have no way of determining the pcm bit rate since neither receiver I own will display this information with a 4k or 3rd generation Apple TV.
 
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If you install the Developer HUD on your Apple TV you can see the bitrates when the Apple player software is used. Other players, such those as Infuse, may not show HUD information.
 
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@HDFan , thanks for the tip. I enabled the developer settings. I tested audio bit rate with Netflix and Alien Covenant 4k. Trying various movies gave me an average bit rate of 384 kbps for a few movies. Now I'm debating whether I should get a new receiver as it may not result in any sound improvement over my current receiver.

Anyone notice a difference in sound quality with a 5.1 system between running a receiver between the Apple TV and HDTV using only HDMI vs Apple TV connected directly to the HDTV with optical from HDTV to receiver?
 
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If the Apple TV ever supports more advanced audio codecs, such as DTS-MA or Dolby TrueHD, they aren't supported via optical:

https://www.lifewire.com/digital-optical-connection-1846881

"It is important to note that digital audio signals, such as 5.1/7.1 multi-channel PCM, Dolby Digital Plus, Dolby TrueHD, Dolby Atmos, DTS-HD Master Audio, DTS:X, and Auro 3D Audio cannot be transferred via Digital Optical connections - These formats require HDMI connections."

Don't know if this would limit the audio quality of a specially written app such as Infuse.

And, of course, if you are using a Blu-Ray player connected to your TV then you would have the same issue.
 
HDFan said:
If the Apple TV ever supports more advanced audio codecs, such as DTS-MA or Dolby TrueHD, they aren't supported via optical:
Click to expand...
This is true, but if you think of it - it has been created intentionally.
There is no way a light cable can not achieve bitrates of a copper cable. So throughput should not be an issue.
It is the (lack of) copy protection schemes that HDMI sports.
Makes me wonder why didn't they come up with enhanced optical link, that could have had all the missing features like copy protection and capabilities negotiation? Could it be because of mechanical "clumsiness" and cost of optical connectors?
 
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