Article: What AirPlay 2 Means for Your Listening Setup

[The Computer Audiophile]

I think a clarification should be made that AirPlay doesn't do the resampling to 48 kHz but rather the resampling is device dependent. Streaming via AirPlay to any number of HiFi devices will pass 44.1 kHz no problem and even the AirPort express is 44.1 kHz. Only the AppleTV resamples the audio to 48 kHz.

[Ralf11]

5 hours ago, Dr Tone said:

 

You just said it upsampled 16/44.1 to 16/48.  That can be done well or it can also be done poorly.

 

On this fact alone you can't say it doesn't affect sound quality.

 

can you explain how this would affect SQ?

[Dr Tone]

8 minutes ago, Ralf11 said:

 

can you explain how this would affect SQ?

 

Upsampling filters have subtle sound differences.  That's what Jussi's HQPlayer is all about.

 

Intersample overs if not enough headroom is applied when upsampling.

[new_media]

3 hours ago, PeterG said:

My preconception is based on Apple's history, not AirPlay per se.  I trust that you understand why iPhones, iPads, iTunes, etc might have given me this notion. 

I'm not following. What does the history of these devices have to do with AirPlay passing a lossless digital audio stream?

 

I believe Stereophile reviewed the original AirPort Express way back when (2004?) and found the digital output to be bit perfect. 

[The Computer Audiophile]

2 hours ago, new_media said:

I'm not following. What does the history of these devices have to do with AirPlay passing a lossless digital audio stream?

 

I believe Stereophile reviewed the original AirPort Express way back when (2004?) and found the digital output to be bit perfect. 

We did it in 2012

 

 

[phunge]

Great writeup from Brian of Roon Labs regarding some of the limitations of Airplay (contrasted with Roon's RAAT) here:  https://community.roonlabs.com/t/whats-the-difference-raat-vs-airplay/6891/5

 

I wonder if Airplay 2 solves any of these issues?  Especially the use case of streaming to a stereo pair of devices -- how do they handle clock variance between the two devices?

[feelingears]

In reading about AirPlay and Airport Express for years here at CA and elsewhere, there are consistent, dogmatic statements made about the tech, lack of tech, and the sound quality of said tech spec. ?

 

The statements are mostly negative. The statements, pro and con, are made by randos like me and by industry leaders who shall remain nameless (but you can look 'em up with a little search prowess).

 

One of these days I will stop enjoying my system and really put it to the test, but for now, I'll just say wi-fi to optical to Recovery (yeah, upsamples) powered by LPS-1 out via coax to DAC is awesome. Based on a fair bit of critical and casual listening, I preferred this chain by a hair to AEx Ethernet to mRendu to DAC. As I said, maybe I'll get around to direct USB now that my DAC is a well-known/well-regarded make and model, but it's simply so great to enjoy. And, it hangs with my LP playback. I like digital and vinyl now as siblings (where as before I felt they were cousins). And I am interested in what the next audio step is, so perhaps writing this will get me off my rear.

 

So just saying that I appreciate the desire to get to the bottom, er, top of Apple hardware and software's ability to perform seeing as how the combo is like MS Office–everywhere and "free." I know that one day, probably sooner rather than later, Apple will do something to iTunes that will drive me away permanently and I'll be needing a new software and hardware solution for playback. Right now Auralic's Aries seems to be the best contender, but that's for the future "Best Alternative to iTunes now that ____" thread.

 

 

 

 

[kirkmc]

7 hours ago, phunge said:

Great writeup from Brian of Roon Labs regarding some of the limitations of Airplay (contrasted with Roon's RAAT) here:  https://community.roonlabs.com/t/whats-the-difference-raat-vs-airplay/6891/5

 

I wonder if Airplay 2 solves any of these issues?  Especially the use case of streaming to a stereo pair of devices -- how do they handle clock variance between the two devices?

 

Um... (From the article you link to.) 

 

Quote

AirPlay started its life as a feature of the AirPort Express. It evolved into an audio distribution system a few years later. It is hobbled by trying to fit into the performance envelope of the embedded devices of yesteryear, and it’s cobbled together–a mishmash of hacked up versions of several well-known protocols, with very little coherence to the overall system design. It looks like what it is: an overgrown feature masquerading as infrastructure. It’s stretched pretty thin, at this point, and it hasn’t evolved in a long time.

 

 

Where to begin. AirPlay started out as AirTunes, and it wasn't a "feature" of the AirPort Express, it was a feature of iTunes, and then Mac OS X; the AirPort Express was the first hardware device to support it. The language he uses - "hobbled by trying to fit into the performance envelope of the embedded devices of yesteryear, and it’s cobbled together–a mishmash of hacked up versions of several well-known protocols, with very little coherence to the overall system design" - shows that he doesn't really understand what it is. Since it is proprietary, he can't know what protocols are used, and the words he uses - "hobbled" and "cobbled" - while presenting nice alliteration, make it clear that he's not very objective. 

 

He essentially goes no the criticize the fact that it is a proprietary format; which is a valid criticism, but has nothing to do with audio quality. But of course he's touting his own proprietary format, so what do you expect? 

[kirkmc]

12 hours ago, The Computer Audiophile said:

I think a clarification should be made that AirPlay doesn't do the resampling to 48 kHz but rather the resampling is device dependent. Streaming via AirPlay to any number of HiFi devices will pass 44.1 kHz no problem and even the AirPort express is 44.1 kHz. Only the AppleTV resamples the audio to 48 kHz.

 

Yes, you're correct. My apologies for that slip. Oddly, Apple doesn't publish any detailed information about how AirPlay works on its developer site; not even the fact that it converts audio to Apple Lossless, let alone upsampling. This said, if you stream movie audio (which is 48 kHz) from the Apple TV to the HomePod, it's not clear whether the Apple TV downsamples it, or whether the HomePod can play that sample rate. 

[miguelito]

On 6/4/2018 at 11:22 AM, The Computer Audiophile said:

I did a bit more digging on this, as streaming audio through the phone is my pet peeve. It appears that AirPlay 2 as of right now doesn't really help and requires the phone still be heavily involved with playback in most cases.

 

The HomePod can stream right from the cloud under certain circumstances, but all other audio routes through the phone. Spotify and Tidal have had this nailed for years by sending audio straight from the cloud to the playback device. 

 

 

For the geeks, here is a link to a developer video and PDF.

 

https://developer.apple.com/videos/play/wwdc2017/509/

 

509_introducing_airplay_2.pdf

 

 

Paging @DarwinOSX - It seems AirPlay 2 still requires the phone pretty heavily. Do you have any other information?

I don't think Airplay 2 can solve the issue of not using the phone for streaming - the Spotify and TIDAL cases both require a client to be present in the device that does the streaming. I would expect such a client to exist in the Homepod only for iTunes streaming.

[kirkmc]

1 minute ago, miguelito said:

I don't think Airplay 2 can solve the issue of not using the phone for streaming - the Spotify and TIDAL cases both require a client to be present in the device that does the streaming. I would expect such a client to exist in the Homepod only for iTunes streaming.

 

The HomePod client is for Apple Music streaming, not iTunes (though perhaps you conflate the two). You can stream from iTunes on any computer to the HomePod as well, but that's push streaming, not pull. 

[Jud]

10 hours ago, kirkmc said:

...and the words he uses - "hobbled" and "cobbled" - while presenting nice alliteration, make it clear that he's not very objective. 

 

They rhyme, they're not alliterative.

 

OK, sorry. 

 

[Cebolla]

On 6/5/2018 at 2:15 PM, kirkmc said:

On 6/5/2018 at 2:10 PM, Dr Tone said:

You just said it upsampled 16/44.1 to 16/48.  That can be done well or it can also be done poorly.

On this fact alone you can't say it doesn't affect sound quality.

Apple has been doing this for years; it's not new. I'm not aware of any complaints about it not sounding good.

 

Although AirPlay (1) has had the potential to stream ALAC encoded audio at various sample rates, AirPlay's ALAC network stream has always been fixed at 16/44.1kHz. Any 'special case' upsampling to 16/48kHz was done at the receiver end by devices that required it for their own purposes, such as the later versions of the AppleTV.

[Ralf11]

any info on what exactly the CoreAudio framework is and what it does?

[Dr Tone]

12 minutes ago, Ralf11 said:

any info on what exactly the CoreAudio framework is and what it does?

 

You asked for it.

 

https://developer.apple.com/library/archive/documentation/MusicAudio/Conceptual/CoreAudioOverview/WhatisCoreAudio/WhatisCoreAudio.html

[miguelito]

20 hours ago, kirkmc said:

 

The HomePod client is for Apple Music streaming, not iTunes (though perhaps you conflate the two). You can stream from iTunes on any computer to the HomePod as well, but that's push streaming, not pull. 

Yes, that’s what I meant - Apple Music Streaming - not the standard airplay protocol which has worked fine for a very very very long time.

 

In fact, at home I have been able to do this multi room streaming from any airplay device for years using RogueAmoeba’s Airfoil and Airfoil Speakers. 

[kirkmc]

2 hours ago, miguelito said:

Yes, that’s what I meant - Apple Music Streaming - not the standard airplay protocol which has worked fine for a very very very long time.

 

In fact, at home I have been able to do this multi room streaming from any airplay device for years using RogueAmoeba’s Airfoil and Airfoil Speakers. 

 

And you could stream to multiple devices from iTunes for many years. What AirPlay 2 does is improve sync and increase buffer size to prevent dropouts. 

[miguelito]

44 minutes ago, kirkmc said:

 

And you could stream to multiple devices from iTunes for many years. What AirPlay 2 does is improve sync and increase buffer size to prevent dropouts. 

If your network is properly done you do not have dropouts. I don't recall the last time I had an Airplay dropout, and I have two rooms playing via Airport Expresses over wifi. So much expectation and it is just a larger buffer?

 

What would be interesting to me - although probably not possible - is a sync to other mechanisms. For example I would like a way to stream to SONOS together with Airplay in a sync'ed way (the SONOS part over UPnP).

 

SONOS is going to be adding Airplay 2 to some of their speakers, but whether that would mean that they would play in sync with other Airplay devices is yet to be seen though.

[kirkmc]

1 minute ago, miguelito said:

If your network is properly done

 

And what does "properly done" mean? In spite of your good intentions, your router may not be sending data perfectly all the time. I don't get dropouts on mine, but I hear from a lot of people who do. 

[miguelito]

4 hours ago, kirkmc said:

 

And what does "properly done" mean? In spite of your good intentions, your router may not be sending data perfectly all the time. I don't get dropouts on mine, but I hear from a lot of people who do. 

My home LAN has an airport extreme as a router, wired to a gigabit switch, which then wires to an airport extreme in the office and another one in the master bedroom. My airplay devices in the master bedroom (two-bedroom and bathroom) are connected to the bedroom airport extreme over wifi and serve two powered speaker sets. So I have airplay devices that are wired to the network as well as some that are connected over wifi (airport expresses in both cases). 

 

I have never, not once, experienced a dropout when playing over airplay to multiroom (4 rooms) via iTunes or via Airfoil. My apartment is ~3000 sq ft.

[Ralf11]

Using my Apple TV3 and remote to control or pull? from my computer is flawless

 

Using either computer to try and push? music or video with the "AirPlay to" icon on the computer always causes dropouts - that's with 2 different routers I've used.

[phunge]

On ‎6‎/‎6‎/‎2018 at 3:24 AM, kirkmc said:

- shows that he doesn't really understand what it is. Since it is proprietary, he can't know what protocols are used

 

Hmmm, not sure why you try to discredit him?  Is it because he criticized your beloved and infallible apple?  Surely Roon's CTO must understand the protocol having built Roon with the ability to stream to airplay devices.  The protocol is no secret, it was reverse engineered only a few years after it's release.  Even the private key used by apple's symmetric AES encryption to provide DRM has been leaked.  I also think it's no secret that the protocol is 15 years old, was originally designed to handle audio only, and has been evolved since to add support for additional, non-audio features such as video, mirroring, etc.

 

Anyway, the issue of Brian's understanding (or lack of) notwithstanding -- I don't think there is any dispute on apple's choice of clocking scheme within the original airplay protocol.  As with S/PDIF or non-asynchronous USB, airplay dictates the clock comes from the source.  The source pushes the audio to the DAC, and embeds the clock, in the same manner as S/PDIF.  This requires the DAC to either synchronize it's clock to the source clock (phase locked loop & voltage controlled crystal oscillator), modify the audio stream to deal with buffer under/over runs (add or drop samples), or provide some form of Asynchronous Sample Rate Conversion (convert the data from the source freq to the DAC's frequency). 

 

In the early days of digital, the 'bits are bits' argument was ever present.  If the same audio samples are being sent, unmolested, to the DAC, then things should sound the same.  In S/PDIF, however, it is not just the audio samples that are being sent to the DAC, the clock is also embedded in the protocol.  While it was possible for the DAC to recover and use the incoming clock, high-end DAC manufacturers started implementing reclocking.  Incoming samples are placed in a buffer, and a phase locked loop was used to lock to the incoming clock.  Rather than using the incoming clock directly, the DAC would generate it's own clock utilizing a voltage controlled crystal oscillator, adjusting it's frequency slightly to match the timing of the incoming clock to avoid any buffer under/over runs.

 

Being that this is computer audiophile, most will likely be familiar with the advances of asynchronous USB audio pioneered by Gordon Rankin, Ayre and dCS.  The idea with asynchronous USB is to put the DAC in charge of the clock.  The clock can be physically located in close proximity with the DAC on the circuit board, or a high quality outboard clock can be included in the system.  The DAC then pull's the data from the source at it's own rate.  Most high-end DACS these days include some form of asynchronous USB implementation, and I think it is generally accepted that this design allows for a more stable, lower jitter clock which improves overall sounds quality.  

 

Letting the DAC control the clock would be difficult/complex with a stereo pair of devices, however.  Drift in multi-room audio is less of an issue if kept fairly low (e.g. <1s), but even miniscule drift between stereo devices would be detrimental to sound quality.  having a stereo pair of devices with independent clocks requires some form of clock synchronization to keep them in sync.  I don't know how Apple has implemented this with the Airplay 2 protocol, but I would be interested to find out.  If they have changed the clocking scheme, I would be pleasantly surprised.  

 

For the average apple customer interested in running two homepods as a stereo pair, this discussion is pointless -- most people just don't care.  For the average computer audiophile participant, however, I suspect that these issues become an interesting aspect of the hobby.  Those interested in the state of the art of digital audio streaming will likely want to look beyond apple's 15 year old airplay technology.  Roon's RAAT protocol or OpenHome/UPNP are likely better choices but I would be interested to learn more technical details about what Airplay 2 brings to the table.

 

 

[BerwynDad]

Kirk - Has their been any indication as to when or if iTunes will be able to serve up music with AirPlay 2? I found it very strange that AirPlay 2 software release (iOS 11.4 and the AirPort firmware) last week did not include an iTunes update.

[kirkmc]

Just now, BerwynDad said:

Kirk - Has their been any indication as to when or if iTunes will be able to serve up music with AirPlay 2? I found it very strange that AirPlay 2 software release (iOS 11.4 and the AirPort firmware) last week did not include an iTunes update.

 

Yes, I was very surprised by that. I expected it to be in last week's macOS update, and it wasn't. It's not in the Mojave beta either. I have no idea why there's a delay. 

[BerwynDad]

7 minutes ago, kirkmc said:

 

Yes, I was very surprised by that. I expected it to be in last week's macOS update, and it wasn't. It's not in the Mojave beta either. I have no idea why there's a delay. 

 

My use case is the "classic" approach - I push iTunes music to multiple AppleTVs and an AirPort Express connected amp. I control it all with the iTunes Remote app. My AirPort Extreme driven network is pretty solid with no dropouts.

 

I'm hoping that this usage scenario is upgradable to AirPlay 2 with some combination of new hardware. While it would be nice, I'm not holding my breath for an AirPort firmware upgrade...