ATSC 3.0 audio upgrade

ATSC 3.0 Forum
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tallLeRoy
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Re: ATSC 3.0 audio upgrade

Post by tallLeRoy »

I too hear a great deal of extra bass on the ATSC 3.0 channels. And that is when I am listening on a stereo system through an Apple TV 4K (2017) with a receiver and full range speakers.

LeRoy

DSperber
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Re: ATSC 3.0 audio upgrade

Post by DSperber »

Just for a visualization, here is a comparison of what 5.1 from the ATSC 1.0 (natively passed-through from ATV4K to the AVR for AC-3 decoding) version of a channel looks like as compared to how it currently looks when the ATSC 3.0 version of the channel is tuned and the AC-4 5.1 is sent up/back through cloud-assisted transcoding and then out to the AVR again as "synthesized" AC-3 5.1.

Image Image

That is what you are "hearing" which sounds like "extra bass" and "boomy". All channels are essentially receiving audio at almost the same loudness level, with most of them being fed content that doesn't really belong there. For example, look at the SW and LS/RS levels!

Playback on 2.0 speakers instead of a 5.1 system is similarly "overloaded" but only on the two channels.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

We have made two changes to the handling that will be in the next release:
1) The rear channels have been adjusted to be 20dB down vs the main channels (23dB down for a mono source).
2) The subwoofer low-pass filter has been improved.

If you have a show with notable center or rear channel power the total power will be higher than the original 5.1 due to the ATSC spec for 5.1 to stereo conversion.

When delivering stereo content on 5.1 speakers the HDHomeRun app maintains the same total RMS power. With the new changes a small amount of power is delivered to the rear speakers (20dB down) and the remaining power is delivered to left/center/right. For a mono source each rear speaker gets the audio track down 23dB and the remaining power is split equally between left/center/right.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

The new stereo on 5.1 speakers handling has been released for Windows 10.

aaronwt
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Re: ATSC 3.0 audio upgrade

Post by aaronwt »

Thanks. I'll try it out tonight.

ppasteur
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Re: ATSC 3.0 audio upgrade

Post by ppasteur »

nickk wrote: Fri Jan 21, 2022 11:44 am We have made two changes to the handling that will be in the next release:
1) The rear channels have been adjusted to be 20dB down vs the main channels (23dB down for a mono source).
2) The subwoofer low-pass filter has been improved.

If you have a show with notable center or rear channel power the total power will be higher than the original 5.1 due to the ATSC spec for 5.1 to stereo conversion.

When delivering stereo content on 5.1 speakers the HDHomeRun app maintains the same total RMS power. With the new changes a small amount of power is delivered to the rear speakers (20dB down) and the remaining power is delivered to left/center/right. For a mono source each rear speaker gets the audio track down 23dB and the remaining power is split equally between left/center/right.
Is it not possible to decode the AC-4 audio "one to one" to AC-3. 5.1 to 5.1 with levels intact? Then let the receiving device/client handle it from there?
I would guess not, or you would do it. But, I had to ask.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

ppasteur wrote: Fri Jan 21, 2022 3:14 pm Is it not possible to decode the AC-4 audio "one to one" to AC-3. 5.1 to 5.1 with levels intact? Then let the receiving device/client handle it from there?
It is something I really want to see in the future but it isn't possible at the moment.

DSperber
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Re: ATSC 3.0 audio upgrade

Post by DSperber »

nickk wrote: Fri Jan 21, 2022 12:24 pm The new stereo on 5.1 speakers handling has been released for Windows 10.
Tried out the new HDHR for Win10.

Image

No longer anything on LFE, LS and RS. Everything is now on L, R and C.

Of course it looks like L, R and C are pretty much identical levels, all the time. I will see if I can find some channel content that's actually true 5.1 with differences in these three channels, but for now there seems to be zero "directionality", even just left or right as there is when simple 2.0 stereo is played.

Ok. I've looked at some assorted things now, including live and recorded. Definitely appears to be 3.1 now, not 5.1. LS and RS are seemingly fully shut down.

Also, the channel mix is still very much "non-directional", with the same content (or at least levels) seemingly coming out of all three front speakers. Sounds better than the previous "faux 5.1" I agree.

Note that the LFE channel is not necessarily reduced by 20db as predicted. Seems to vary depending on original content. For example here is the "loudness" from the theme song during the opening of "Friends", with all four channels populated equally:

Image

And here are some other captures. Seems that LFE present or low or absent is very much dependent on underlying content. Interestingly, commercials seem to mostly cause LFE to be right up at 100% of the other three channels. Regular program content sees LFE mostly disappear. Definitely L/R/C are now pretty much the same levels during the program itself.

Image Image

Image Image

But it definitely sounds better in this new 3.1.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

There is content on Ls and Rs channels however it is 20dB down from the source stereo channels.
The LFE channel has the same RMS power as the combined source stereo channels for low frequency content (80Hz 3dB cutoff).

signde
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Re: ATSC 3.0 audio upgrade

Post by signde »

i will start by saying i appreciate that feedback is being taken into consideration and adjustments are being made. i also appreciate all the effort that went into the cloud transcoding service which without it most folks probably would not have audio, so don't take this comment as ungrateful.

i tried out the new app on the xbox one x. it is better than before in my atmos setup - there is no longer blaring audio from the rear surrounds so it is an improvement.

having said that, it still seems wrong. as dsperber pointed out, there's no directionality across the front stage. if i put my ear up to the speaker i can still hear the same audio over the rear surrounds, albeit at greatly reduced volume. again this feels like the same stereo audio tracks just at different volume levels across all 5 speakers. i'm not an audio engineer but i have had surround sound systems for 30 years starting with the original dolby pro logic back in the 90s and this just doesn't sound right. even something as old as pro logic at least gave separation across the front 3 speaker sound stage along with the mono surrounds.

i'm at a loss for the reasoning behind doing this faux 5.1 sound at all - sure seems like a lot of effort on hdhomerun's part for something that isn't really surround sound at all. why not just leave it as 2 channel stereo and let anyone with a multichannel setup do what they want with it? modern AVRs will let you choose faux surround and other modes that attempt upmixing something similar to the old dolby pro logic separation.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

signde wrote: Sat Jan 22, 2022 11:03 am having said that, it still seems wrong. as dsperber pointed out, there's no directionality across the front stage. if i put my ear up to the speaker i can still hear the same audio over the rear surrounds, albeit at greatly reduced volume. again this feels like the same stereo audio tracks just at different volume levels across all 5 speakers. i'm not an audio engineer but i have had surround sound systems for 30 years starting with the original dolby pro logic back in the 90s and this just doesn't sound right. even something as old as pro logic at least gave separation across the front 3 speaker sound stage along with the mono surrounds.
If the source content is near mono (5.1 but mostly center channel before the stereo conversion, or L and R are near identical) then L/R/C will be near identical.
signde wrote: Sat Jan 22, 2022 11:03 am why not just leave it as 2 channel stereo and let anyone with a multichannel setup do what they want with it? modern AVRs will let you choose faux surround and other modes that attempt upmixing something similar to the old dolby pro logic separation.
That is exactly what we do - by default the HDHomeRun app outputs audio using AC3 passthrough to the AVR. This AC3 content is stereo when utilizing the cloud transcode service - it is up to the AVR to utilize the 5.1 speakers from the stereo source.

If you are playing content that switches back and forth between 5.1 and stereo (ATSC 1.0 channels do this or ATSC 3.0 channels when the client has ATSC 3.0 audio codec support) then the content delivered to the AVR using AC3 passthrough will change back and forth between 5.1 and stereo matching the source.

If AC3 passthrough is disabled or not available then the HDHomeRun app generates PCM matching the number of speakers. It does this because most platforms can't switch or can't cleanly switch between 2-channel and 5.1 channel PCM mid playback.

Example - say you sit down to watch a movie on TV - the movie is 5.1 surround sound, you have a surround sound setup, and the sound is decoded locally by your client device (AC3 passthrough disabled and not using cloud transcode). You starting watching a minute early so you don't miss the start, so you catch the last bit of the previous show or you catch an advert before the movie. If that first content is stereo and the app were to set up for stereo PCM output you would be stuck watching the movie in stereo. Instead the HDHomeRun app detects that you have 5.1 speakers and sets up for 5.1 - that way when the content switches to 5.1 you get the full 5.1 experience.

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nickk
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Re: ATSC 3.0 audio upgrade

Post by nickk »

We have confirmed an issue with AC3 passthrough audio channel handling on Android in recent releases - the problem has been fixed and will be in the released planned for next week.

Nick

ppasteur
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Re: ATSC 3.0 audio upgrade

Post by ppasteur »

nickk wrote: Sat Jan 22, 2022 5:53 pm We have confirmed an issue with AC3 passthrough audio channel handling on Android in recent releases - the problem has been fixed and will be in the released planned for next week.

Nick
Thanks for continuing to work this Nick !!

THRAVS
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Re: ATSC 3.0 audio upgrade

Post by THRAVS »

I am using version 20220114a on an NVIDIA Shield that is connected to a Yamaha RX-V485 receiver. Houston now has 10 stations broadcasting in ATSC 3.0. On one or two of them, the audio is not in sync with the video. This is most consistent on the Fox affiliate (26). Since the other stations are generally in sync, I assume that the issue is with the broadcaster signal and not the application. If it is with the station, it would surprise me as I would think that the station engineer monitors the broadcast signal.

The receiver is set to "Straight" (no additional signal processing) and shows 5.1. The Shield has pass through set with Dolby processing turned off. Is this the correct?

The audio is louder and has more bass than ATSC 1.0 sources. The volume level seems to have improved somewhat with this version. As others have stated, the content on each audio channel is not what I would expect from 5.1. Will the next Android version address this?

signde
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Re: ATSC 3.0 audio upgrade

Post by signde »

nickk wrote: Sat Jan 22, 2022 5:53 pm We have confirmed an issue with AC3 passthrough audio channel handling on Android in recent releases - the problem has been fixed and will be in the released planned for next week.

Nick
running the latest app 20220124, shield tv pro passthrough audio seems to be as expected. with ac3 passthrough on, my AVR reports dolby digital 2.0 and i am getting stereo audio, so no "faux 5.1".

this is a major improvement, thanks for the quick turnaround.

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