Apple AirPlay
Compared to the lo-tech, super-simple task of putting a record on a spinning platter, and lowering a needle into the groove, the world of music streaming is bewilderingly complicated, with many competing technologies, standards and products promising to deliver the best possible performance at the best possible price. One which always comes up in conversation with our clients is Apple’s “AirPlay”. This article answers all the common questions we are asked, and should provide you with all you need if you are already invested in the Apple ecosystem, or are planning to do so.
What is AirPlay?
AirPlay is Apple’s proprietary system for distributing music and video wirelessly.  It means you can select and control music, movies, YouTube content, and much more from your iPhone, iPad or MacBook, but listen to it or watch it anywhere in your house, with a bigger picture and better sound.
The ability to stream audio data wirelessly was made available for Apple devices as “AirTunes" all the way back in 2004. In 2010 this was updated to support video as well as audio, and was rebranded AirPlay, and in 2018 with the release of iOS 11.4, was upgraded to AirPlay2, which at the time of writing is the latest and greatest.
What’s the difference between AirPlay and AirPlay2?
The main difference between AirPlay and AirPlay2 is that with AirPlay2 it’s possible to send music to more than one destination, and control the volume of each destination independently. It also allows the source device to receive a phone call without interrupting the music.
How does it work?
For the context of this article, I'll confine my answers to audio. Any app on a phone, or iPad, or Mac has the ability to flag the sounds it creates as “long form”. Long form sounds are different from system noises and notification sounds.  Examples of long-form audio would be a podcast, an audio book, content from YouTube, music being played from an iTunes library, or from a streaming platform. Any app which produces or consumes long-form audio can make use of the AirPlay system to create a stream containing the digital data that makes up that audio and transmit it, unchanged, over a wireless network to a receiver, which then decodes it and plays it. Alongside the music data, metadata can be sent which determines the volume of the playback on the target system, so the music doesn’t suffer degradation in transit.
How good does it sound?
At a technical level, the sender is sending “CD quality” audio - the digital data is held in a 16 bit word, sampled at a rate of 44100 times a second.  For more information on this and related subjects, check out my article on Digital to Analogue converters (DACs). So, in theory the music sounds as good as a CD, which is potentially very very good indeed. Of course, the quality you experience will depend on the receiver and how that music is replayed. However, the key point is that there’s no signal alteration or lossy compression involved - the audio generated by the sender will be identical once it reaches the receiver. Once the stream has been retrieved and decoded, we have the original digital representation of the music, which can be fed to whatever combination of DAC, amplifier, and loudspeaker you like.
How does it compare to Bluetooth?
There are two important differences when comparing AirPlay to Bluetooth.
Firstly, Bluetooth is designed as a point to point direct connection. It’s effectively a very low power radio transmitter and receiver combination, and in domestic settings its range doesn’t extend beyond about ten metres. It’s not very tolerant of obstructions and interference, so if you move rooms, or put something in the microwave, there’s a good chance you’ll get signal interruption, and your music will stop or playback seem to skip. By contrast, AirPlay uses your existing WiFi network; if you have WiFi signal, the music will be transmitted uninterrupted, and in a large house it’s easy to extend and grow your network to ensure coverage throughout the building.  
Secondly, the music is always compressed and altered to some extent when using Bluetooth. Bluetooth was actually invented in 1994, and was never designed with music playback in mind. Its bandwidth is appropriate for compressed voice calls, but it’s nowhere near wide enough to accommodate the complexities of music. In order to allow the music to be transmitted over the air waves at an acceptable quality, the signal has to be altered in a number of ways. A lot of time has passed since the invention of Bluetooth, and there are now creative digital solutions to attempt to squeeze higher resolution through the Bluetooth virtual pipe. We'll discuss this in a future article. However, even at its very best, while music transmitted over Bluetooth using the aptX or aptX HD codecs can be extremely good, fundamentally the signal is changed, and in both scientific and subjective listening tests the results are definitely different, and to most ears not preferable to a system in which the signal is not compressed or altered. Because AirPlay, by contrast, doesn’t in any way alter the signal, the bits your application sent to the receiver by the sender are exactly the same as the ones your sender received from, e.g. Tidal - that compromise simply isn't there.
Can it do multiroom?
Sort of. The original AirPlay only supports sending one source of audio (or video) to one receiver. AirPlay2 adds the ability to send data and independently control the volume of multiple destinations, but unless you are an Apple Music subscriber, you can’t select different source material from one device. If you want genuine multiroom (the ability to independently to control both what is played and at what level in multiple zones) and you have a preference for an alternative source of music than Apple, you should consider a different solution.
Does it work without Apple products?
Actually, yes! Apple is now licensing the system, and is actively promoting integration with other products, as part of its quest to be considered the first stop for home automation. Within the context of music and movies, there are speakers, receivers and televisions which can accept and play stream.
Receivers which can be integrated with the rest of your HiFi/AV system that support Airplay include the Primare NP5 Mk2, all the Bluesound models, all the Arcam AV products, and their SA30 streamer and integrated Solo Uno.
If you want just speakers, the Bluesound Pulse range, the KEF LS50 II and LSX II and all the Harmon Kardon Citation range can receive an AirPlay2 stream.
If you’re technically minded, it’s also possible to build a small device using a raspberry pi to receive and decode the proprietary stream from an Apple device.  This can then be connected to a DAC or amplifier. The extent to which you are comfortable with either the technical challenges or the ethical challenges is very much a personal matter, but it’s possible.
Does it support non-Apple streaming services?
Yes - any developer can integrate with the AirPlay stack, and all the major streaming services have taken advantage of this capability. If your phone or computer has access to a streaming service such as Tidal, Qobuz or Spotify, it can retrieve the music from that service, and then stream it to the destination. Again, for true multiroom capabilities, you’ll need to use Apple Music, and for best integration with Siri, again, you need to stay in the Apple ecosystem, but you’re absolutely not tied to Apple, and you don’t need any extra software or setup steps to use your streaming platform of choice.
What about hi-res audio?
If your source music is a hi-res format - ie the sample rate is higher than 44.1 kHZ and/or the word length is greater than 16 bits, the sending device will down-sample it to 16/44.1. So if you have a high res source file that you bought and downloaded to your computer or phone, or if you subscribe to a streaming platform such as Qobuz or Tidal that can stream 24-bit master files, you won't get the benefits of the extra resolution, but it will still be at a similar level of quality as if you had the music on CD.
How do I get started?
Because AirPlay is based around the idea of a sender and a receiver, you're going to need at least two devices. Any Apple device from the last dozen or more years will support original Airplay, and anything running iOS 11.4 or later will support Airplay 2. For most people the sender will be an iPad or iPhone, so if you have one already, you’re already sorted on the sending side. On the receiving side, you have a couple of options. If you already have a TV and AV/Hifi system, the simplest way is to add an Apple TV - you can now set that as the AirPlay target, and your music will be processed and reproduced by your AV or Hifi system. If you want to add AirPlay functionality to an existing hifi system, but don’t have a TV in the mix, you can add a Primare or Bluesound device, which will function as the receiver, and will either act as a DAC and send analogue output to your amplifier, or send the digital data to a DAC already in your system. If you’re starting afresh, one compelling option is to invest in a pair of high quality active speakers that support AirPlay2 such as the exceptional KEF LS50 II or LSX II - you'll have audiophile quality with no speaker cables or interconnects anywhere!  Similarly if you want to add a system to a second room such as a kitchen or bedroom, the simplest approach would be to use the Arcam Solo Uno with either a pair of in-ceiling or in-wall speakers, or some discreet bookshelf speakers such as the SVS Prime Bookshelf. If you just want a speaker or pair of speakers, the Bluesound Pulse Flex 2i is great, costing slightly less than Apple's HomePod, and sounding better. For a real budget option, the HomePod Mini at £99 is hard to beat.
Apple's AirPlay technology is convenient, easy to use, and well-integrated with leading HiFi and home cinema brands. It's not the last word in true multiroom, and it doesn't support hi-res audio. It also has a high cost of entry in requiring an iPhone, iPad or Mac to function as the sender, so it's far less attractive if you're not already an Apple user. However according to statcounter, 51.64% of the UK own an iPhone, so if you're part of that majority, and you want a simple and effective way to enjoy streamed music with audiophile quality, AirPlay is a great place to start.

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