Pop quiz, kids: when was the last time you saw a fancy new portable speaker system with an actual, physical smartphone dock? If you have an immediate answer to that question, either you work for the manufacturer that makes said device, or you spend way too much time reading consumer electronics news sites (not that there's anything wrong with that). The fact is, the physical docking connector is going the way of the dodo for anything other than charging and file syncing. If you're playing music from your smartphone or portable media device (or even your laptop computer) to a self-contained media player, home theater, or multi-room music system, chances are good that you're either streaming it wirelessly or wish you could.
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But how? As with most emerging technological trends, there isn't one universally agreed-upon wireless audio streaming standard. Depending on your portable media source, you may even have a choice of several different methods for moving your music from Point A to Point B through the ether, and not all of them are created equally. Let's look at the salient points for the most common wireless streaming audio technologies, starting with the most ubiquitous.
Bluetooth isn't merely the most common wireless technology used for audio streaming, it's also the simplest - at least in terms of setup and operation. To stream audio from your portable player to a Bluetooth speaker or receiver, you merely need to pair the two devices (a fairly simple and secure process these days that may require you to enter a four-digit password) and press play on your smartphone or other media player. The signal is beamed directly from source to destination, without the assistance of any form of router or other intermediary.
You'd never know it was so simple from looking at the specs list for the average Bluetooth-capable device, though, which is likely to include a mouthful like "Bluetooth v2.1+EDR, Class 2 with SPP, DUN, FAX, LAP, OPP, FTP, HID, HCRP, PAN, BIP, HSP, HFP, A2DP & AVRCP profiles and aptX and AAC codec support" somewhere amongst the rundown of supported formats. Don't freak out. You don't actually need to know what most of those letters and numbers mean. The Class of the device is of interest because it defines the range - in other words, how far your Bluetooth transmitter can be from your Bluetooth receiver. Class 1 devices can have a range up to 100 meters (usually more like 20 or 30); Class 2 devices have a maximum potential range of 30 meters (usually more like five or 10). The reason for all of that other tacked-on jargon is that Bluetooth was originally designed as a short-range personal network - a wireless replacement for RS-232 cables. Enhancements have been added to the technology since its creation to allow it to serve other functions: Human Interface Device Profile (HID), for example, facilitates things like wireless mice, keyboards, and video game controllers, whereas Headset Profile (HSP) provides support for the wireless headsets used with mobile phones. For our purposes, though, the important alphanumerics to focus on are A2DP and aptX.
A2DP (Advanced Audio Distribution Profile) is, simply put, a one-way wireless stereo pipeline between a transmitter (your smartphone, tablet, media player, laptop, etc.) and receiver (your wireless speaker system, AV receiver, dongle, etc.). If your portable device plays music and features Bluetooth, it almost certainly supports A2DP. If a device is marketed as a Bluetooth speaker or Bluetooth add-on for an AVR or other music system, it almost certainly supports A2DP, so you can assume they'll make music together. Beautiful music, though? Maybe. Maybe not. A2DP doesn't deliver a very roomy pipeline for music, which means that the music on your portable media player or smartphone (or computer) probably needs to be compressed before being delivered through the airwaves. By default, A2DP relies on Low Complexity Subband Coding (SBC) to squish the signal, but it can also use other codecs (coder-decoders or compressor-decompressors) to get the job done. One of these is AAC, the codec of choice for iTunes music downloads.
The codec preferred by most Bluetooth streaming aficionados these days is aptX, which purports to deliver near-CD-quality streaming. Not all Bluetooth receivers and speakers support aptX, but many do, as do a number of Bluetooth headphones. Not all media players support it, either. Notably, most HTC and Samsung phones do, but the iPhone doesn't, which brings us to...
Originally called AirTunes back in the days when it merely supported audio, Apple's proprietary content distribution protocol is the music streaming method familiar to most iOS users. AirPlay is in some ways simpler than Bluetooth and in some ways more complex. In its most typical implementation, an AirPlay-capable speaker, AV receiver, Apple TV, or add-on receiver (which can be anything from a dongle to a full-blown Apple AirPort Express is connected to your home network, either via Ethernet or WiFi. Music is streamed via that network from your portable iOS device or directly from iTunes on your computer. In other words, to get music from Point A to Point B via AirPlay, it has to travel through your router (unless you're using AirPlay Direct on an ad hoc network but, my goodness, this article is already getting complicated enough, so let's pretend I didn't type that). That's true whether you're streaming tunes via apps like Spotify or Pandora or streaming the music stored on your iPhone, iPad, or laptop/desktop. My favorite way of employing AirPlay is to use the Remote app on my iPhone or iPad to send files directly from the iTunes library on my computer to the Wireless Music Bridge connected to my Control4 system, but tracing out the networking signals involved there can get a little silly. Any way you go about it, with all involved devices connected to your home network, you simply press the AirPlay button on the source device, select the destination, and you're done. In many cases, AirPlay is built into IP-controllable devices that will power themselves on as soon as they sense an AirPlay signal is headed their way. It's the ultimate in laziness.
Of course, given that it relies on WiFi for wireless streaming, nailing down the range of AirPlay isn't quite as simple as it is with Bluetooth. It really depends on the quality of your network. Assessing its quality is a little easier, though, since AirPlay uses the Apple Lossless codec exclusively, which means that anything up to CD-quality files will be delivered with no lossy compression. Anything better than CD quality will get downsampled to 44.1 kHz.
Of course, using AirPlay also means you're locked into the Apple ecosystem, which has a couple of implications. First, you should probably forget about downloading and streaming FLAC files. I'm not saying it can't be done; I'm merely saying that, if you've read this far into a wireless audio streaming primer, you probably shouldn't try. Secondly, if you go hog-wild buying AirPlay-compatible receivers, speakers, and so forth and then decide to switch to Android down the road, you're stuck with a lot of arguably useless gear. That's just the nature of proprietary systems, and that may be one of the reasons why many manufacturers are gravitating away from AirPlay support. There are similar open-architecture alternatives, though, such as ...
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