Bruins96

macrumors member
Original poster
May 27, 2021
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I'm a subscriber to Apple Music and was very heartened to see them implement lossless, high-resolution lossless (which apparently ATV doesn't yet support), and spatial audio including Atmos output. I have been enjoying several Atmos enabled albums tracks over the ATV4K gen.2 going HDMI 2.1 direct to a Denon 4500h Atmos enabled receiver.

However there is a repeatable glitch/audio dropout issue I can pinpoint to Atmos music tracks. It's likely due to receivers having to "re-detect" the Atmos signal between every track, and while the Denon is no slouch (it's a recent receiver and is in the upper-half of Denon's product line) it still takes a fraction of a second to detect the signal.

Why is this a big deal? Think of an album like The Beatles Abbey Road, where the last half of the tracks blend seamlessly from one song into the next. Now imagine a split second audible pause between each of those songs on the medley. Or Dudamel leading the L.A. Philharmonic through Mahler no.8. An amazing performance and recording, and a wonderful Atmos playback experience. Except that very often classical tracks blend into each other. So again, while in real life the orchestra goes straight from one part of the movement to the next, now there's a split second pause.

If I play albums that are not Atmos, be they lossless or other lower bit rate sound format, there is no discernible pause between tracks that blend into each other. So this does seem to be limited to Atmos tracks, likely due to the complexity and bandwidth of the signal.

Anyone else experiencing this?
 

waw74

macrumors 601
May 27, 2008
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I've tried it both with a Sonos Arc and using the TVs speakers (LG CX oled), using Mahler no 8. (abby road doesn't seem to be in atmos yet). and I had the same issue. I don't see any indication that Atmos is dropping, no blink or anything

they probably just haven't added gapless playback for atmos yet, My guess is it was an oversight.

Gapless is a little harder to do than you would think. MP3s were around for a while before you could do gapless, for a while you had to encode albums as a single track if you wanted it without the pause, It looks like iPod was out for about 4 years before gapless playback was added to it.

my only suggestion for a way to get it fixed...

or a short and friendly email to tcook@apple.com
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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28
I've submitted tickets a few ways to them, but thank you for providing the link as well! I mean it certainly could be the gapless playback issue. But I also find I tend to lose the first second or so of a track when I start to play an Atmos track. So the AVR does take a bit to latch on to the signal (for the record it's a Denon 4500h which is a relatively recent receiver and not an inexpensive model).
 
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waw74

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May 27, 2008
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are you loosing a second or two, or a fraction of a second ?

mine just has a small gap, about the same as a finger snap
way too fast for it to re-lock after signal loss.

at least for me, when I've paused an atmos movie, I sometimes get a noise, or more frequently the audio tracks shift around when I first start. The voices come out of the surround closest to me for half a word, They might be coming out elsewhere too, but that speaker is close, so it might just be that's the one I'm hearing the most.


gapless playback is a bit more complicated than you would think.
 
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anodibu

macrumors member
Apr 12, 2013
67
59
I encountered the same problem listening to Mahler 8 on MacBook with wired headphones. It also happens when I download the album. It’s very short but annoying and distracting on the Mahler 8 with its short tracks blending into each other. Hope they can fix it soon.
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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28
From a cold start, or by manually skipping songs, the drop-out is closer to a second. When continuously playing, it's more like a fraction of a second as one song transitions into another. So I think from a cold start it's a matter of Apple needing to account that most, if not all, audio video receivers need a moment to detect the Atmos signal (maybe baking into the software a short delay to allow for the transmission of the Atmos signal flag to the receiver before beginning playback of the track).

The fraction of a second between tracks during continuous playback may indeed be more related to gapless playback. And I get that it may be more complicated than I think, but I also would think that a two trillion dollar company probably has some pretty smart engineers and programmers on their staff who are more than capable of figuring this out, and honestly probably should have prior to launch.
 
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priitv8

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Jan 13, 2011
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Today, I managed to create a picture like this on my appleTV.
Despite several retries, I have had no luck re-creating it.
What I did - I started playback on iPhone Music app, Hi-Res Lossless and then directed it to AirPlay to my fully turned off HT system. So the aTV woke up, turned on the TV and AVR and showed me this Hi-Res mode on aTV screen.
IMG_1680.jpeg IMG_1679.jpeg
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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Very interesting priitv8.

To go back to my earlier posts, there definitely is an issue with gapless not being implemented as I just listened to that Dudamel/Mahler Atmos soundtrack on my phone, and there is an audible gap/glitch as one movement goes to the next. Much shorter than what I hear on ATV, but definitely noticeable and there, kind of like an electronic version of a record needle skip.
 
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priitv8

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Very interesting priitv8.

To go back to my earlier posts, there definitely is an issue with gapless not being implemented as I just listened to that Dudamel/Mahler Atmos soundtrack on my phone, and there is an audible gap/glitch as one movement goes to the next. Much shorter than what I hear on ATV, but definitely noticeable and there, kind of like an electronic version of a record needle skip.
I also tried and tested it. And it does not seem to be any stream format change (as waw74 correctly points out - the received stream remains PCM Atmos all the time), but rather the change of source (file) on server side.
If I compare it to my own DLNA streaming to a Blu-ray player (to enjoy TrueHD Atmos), then Apple's version is still much better, my bluray player will consistently keep 2-second pauses between the tracks.
So the only solution to fix this is not to slice one gapless piece into separate files but to keep it as one single file.
 
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waw74

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May 27, 2008
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So the aTV woke up, turned on the TV and AVR and showed me this Hi-Res mode on aTV screen.
So it's using the "send a file location" method of airplay, instead of "play on phone and send an audio stream".

not surprising, most if not all of apple's services use this method.
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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I also tried and tested it. And it does not seem to be any stream format change (as waw74 correctly points out - the received stream remains PCM Atmos all the time), but rather the change of source (file) on server side.
If I compare it to my own DLNA streaming to a Blu-ray player (to enjoy TrueHD Atmos), then Apple's version is still much better, my bluray player will consistently keep 2-second pauses between the tracks.
So the only solution to fix this is not to slice one gapless piece into separate files but to keep it as one single file.
Admittedly I don't listen to classical much, but I listen to The Beatles a ton. And streaming the second side of Abbey Road (the "Medley") has not produced gaps on Apple Music prior to Atmos (when I presume it was AAC). And they were certainly not combined into a single file.

In fact going to Sgt Peppers Lonely Hearts Club Band, if you play the (Reprise) which blends into A Day in the Life, there is also no pause, and that's now been upgraded to Lossless (but not Atmos). So there is something wrong with gapless playback in Atmos that isn't present in Lossless and was not present in AAC.
 
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Allyance

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Sep 29, 2017
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East Bay, CA
I have spent the last couple of days listening to all types of music on their curated lists and never once had a drop out. Could it be a streaming problem with your connections?
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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I have spent the last couple of days listening to all types of music on their curated lists and never once had a drop out. Could it be a streaming problem with your connections?
To clarify, I do not get random dropouts. The dropout happens when one track switches to the following track during those "medleys" where one song runs into another (like the last half of the Beatles' Abbey Road, many classical CDs, etc.). It has to do with gapless playback not being properly enabled for Atmos.
 
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ledzep1

macrumors regular
Jan 24, 2016
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I can also confirm these dropouts playing Atmos music from apple music app on ATV4K gen 2.

The dropouts have nothing to do with connection or internet issues as you can repeat the dropout if you rewind to the same point it occurred.
 
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Paul Cordingley

macrumors newbie
Jan 10, 2019
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Sydney, Australia
Yes, I have the same issue, and agree it’s for the reasons stated. Atmos only, my Yamaha receiver has to re-sync for a split-second between tracks. Quite annoying, but at the same time I am in wonder that we can now stream Atmos music, it’s really quite something. Hopefully it can be fixed, it does need to be gapless.

Atmos - Abbey Road is just brilliant, as is Sgt Pepper. Try Yello as well, their latest album is a very good showcase, though the music is not really my bag it is interesting.
 
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priitv8

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Jan 13, 2011
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To clarify, I do not get random dropouts. The dropout happens when one track switches to the following track during those "medleys" where one song runs into another (like the last half of the Beatles' Abbey Road, many classical CDs, etc.). It has to do with gapless playback not being properly enabled for Atmos.
There even used to be a "gapless" option in iTunes and it indeed worked as expected.
Just looking now at the Music.app and the gapless option is gone from there as well.
 
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Bruins96

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Original poster
May 27, 2021
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There even used to be a "gapless" option in iTunes and it indeed worked as expected.
Just looking now at the Music.app and the gapless option is gone from there as well.
I remember using that option when it first debuted (because at the beginning of iTunes it too had the same problem Atmos/Spatial Audio has right now). The option went away when gapless playback was properly implemented in AAC/Lossless playback in iTunes. I used the "gapless check box" in the mid-to-late 2000s but ever since it was taken away (probably in the early 2010s) it didn't matter because by then gapless playback worked flawlessly on iTunes.

Looks like Apple may have forgotten the lessons of ~15 years ago...
 
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Bruins96

macrumors member
Original poster
May 27, 2021
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... or the Atmos stream presents additional difficulties.
I'll start off admitting I'm no audio engineer, so what I'm about to post is completely conjecture and perhaps there is a nuanced difference between Atmos audio streams over the network vs. Atmos on physical media.

I mention physical media because I have a lot of UHD 4K movies on disc with Atmos soundtracks. They all have chapters (i.e. to skip to various points in the film) similar to tracks on CDs (to skip to various songs). You know what doesn't happen if I just watch these movies continuously? A audio gap between chapters.

Again, I recognize streaming Atmos may be a different ball of wax.
 
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priitv8

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Usually those atmos movies are one single file and jump to chapter is undertaken via help file (there are no chapter marks in the MPEG Transport Stream (.ts/.m2ts) file itself). So the player just jumps into new place in the file.
It is true, that the individual frames carry sync markers so the decoder can re-sync to stream in fairly short time (I will not bother to calculate the exact number of milliseconds).
Indeed, it does not help to understand, why is it more difficult (or simply oversight) on the streaming part.
 
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