Sony XAV-AX100
The necessary smarts
You have a three-way choice if you want smart audio system in your car. One is to get, well, a smart audio system for your car. It can have satellite navigation built in, some voice control, interaction via Bluetooth with your phone for hands-free calling and so on. But it may be over-complex and major improvements likely won’t be forthcoming 
too soon.
Or you can choose a slightly dumber audio system which implements either Apple CarPlay or Android Auto. In either case you just plug your phone into the system and the smart stuff is largely performed by the phone. The advantages of this are twofold. First, a modern phone is a super computer and so is going to outperform whatever computing power that you could reasonably expect in a head unit. Second, unless you’re in the habit of swapping out your car head unit every couple of years, it’s going to fall behind the state of the art rapidly. But your phone won’t. The same phone gets regular software upgrades (whether in the OS or the relevant apps), and of course you’re probably going to replace it every couple of years with something 50 percent more powerful than the last one.
So, with all that, what do you go for? It would be clear that I’m leaning towards something which integrates with your phone. But which of those: iPhone or Android? The Sony XAV-AX100 solves that problem: it supports both Apple CarPlay and Android Auto.
Simplicity is best
I’ll return to those matters shortly because apart from them the Sony XAV-AX100 is pretty much a fairly basic car AM/FM radio with support for USB audio and video and Bluetooth audio. Not provided is an analogue auxiliary input for plugging in a non-Bluetooth audio device, and there doesn’t appear to be an accessory CD changer able to be used with it. The concern about such things just goes to demonstrate, I guess, old obsessions of mine.
But of course, there are four amplifier channels, each rated at 55 watts into 4 ohms. And four preamplifier outputs for the main channels, plus an additional one for a subwoofer, so you can boost performance to whatever you might desire. There’s also a video input for a reversing camera, plus a socket for the included microphone to be used for hands-free calling… and other voice interaction.
There’s a 10-band graphic equaliser and adequate channel balancing features, but no time alignment, which means that you may not get the optimum stereo imaging from the driver’s seat in some circumstances.
The Bluetooth connectivity features support for the SBC codec, but none of the higher quality ones (not even Sony’s own highest quality LDAC Bluetooth codec).
But it’s the last bit of connectivity that’s really important: the same USB lead emerging from the rear of the unit which you can use to play USB audio files. An extension lead is provided, so you ought to be able have the working end of the lead out where you need it. Plug in an iPhone and the unit switches over to Apple CarPlay mode, allowing the playing of music from the phone, access to the maps on the phone via the head unit’s display, calling, use of Siri and so on. Similar functions are available for Android phones with Android Auto. The main body of the unit is regular DIN sized, while the display panel – which is about two centimetres deep – is double-DIN in size. The display is touch sensitive, with 800 by 480 pixels of resolution and a diagonal of 163mm. There are few controls on the main unit -- a multipurpose knob that mostly acts as the volume control, and a Home button are the main ones. But a small infrared remote control is included with the system and this allows more control.
Sony XAV-AX100
The screen proved very easy to control, with good touch sensitivity and reliable registration of touches on buttons. Not quite iPhone standard, but the kind of thing that won’t leave you feeling frustrated and irritated. I would have preferred the two main controls to the right of the screen rather than the left in order to reduce the need to stretch. 
While they do more or less the same, there are noticeable differences between Apple CarPlay and Android Auto. The latter, for example, requires an app to be installed on the phone whereas it appears that CarPlay is built into iOS. However, for CarPlay you need to have – according to the head unit’s instructions – the most recent version of iOS, which is version 7.1. For Android Auto you can use any version of Android since version 5.0, which was introduced towards the end of 2014.
From a software management point of view, it probably doesn’t particularly matter. Apple iPhones are pretty insistent about remaining up to date, so almost all iPhones since the iPhone 5 ought to be okay, which goes back to the second half of 2012. Android phones might be more of a problem since Android phones from that far back are unlikely to have been upgraded to Android Lollipop (version 5). So do check your Android phone. It’s quite possible that if it is a little older, it may have Kit Kat, Jelly Bean or even Ice Cream Sandwich (versions 4.4, 4.1 to 4.3 or 4.0 respectively). If you do and the phone’s not too old, there might be a software update available.
Another clear difference was upon first use. When I plugged in the iPhone, it just started working. The Apple CarPlay display appeared on the head unit’s screen and buttons were ready to press, functions to be enjoyed. With Android Auto there were perhaps four or five sets of permissions to grant (just a matter of choosing ‘Yes’ when asked) and two EULAs to approve (End User Licence Agreements), one basically saying that if you kill yourself while using Android Auto, tough bickies, while the other was to do with privacy.
Auto & Play
Later on, when starting ‘Music’ for the first time with Android Auto, I had to choose which music player I wanted to use. It offered Spotify and Play Music as options, but not the standard Music app on my Samsung Galaxy S6. That led to a temporary problem. I sometimes use the Samsung Music app, but mostly a player called ‘USB Audio Player Pro’, which allows high resolution audio output. Neither of those was an option through Android Auto. No matter, except that since I hadn’t been using Play Music (which is a Google app for both streaming music from the Google Music store and for playing music already on your device), the 20-odd gigabytes of music on my phone hadn’t been indexed by it.
So I dropped back out and opened Play Music, let it do its stuff. Next time I plugged it back into the Sony, all was fine. Spotify worked perfectly from the outset. Whichever player app you choose becomes the default, but if you hold the Music icon for a moment, you are given the option to switch to a different one.
Aside from the look of the interface, both Android Auto and Apple CarPlay were pretty much the same in terms of functionality. You just have to remember whether to say ‘Okay Google’ or ‘Hey Siri’ to get at the hands free functions for calling, sending texts, navigating, to start music and so on.
If one has a significant advantage over the other, it probably doesn’t matter anyway in all but the very short term. I expect that the competition between the two is going to be stiff for several years, and they’ll be leap frogging over each other with functions, including improvements in voice control and interaction. For now, the important thing is that both work well. And should you decide to defect from the iPhone to Android, or from Android to the iPhone, this head unit will work with either. Likewise, if your frequent fellow traveller adheres to a different phone OS to you, then it’s just a matter of plugging in the other phone (assuming the Android Auto has been installed in that case).
If you’d rather play USB files, this head unit was a fine device for doing so. Navigation was pretty straightforward using the on-screen interface. There was plenty of information provided on screen (including album art during playback), and the sound was excellent.
The manual listed a fairly impressive range of supported audio codecs: WMA, MP3, AAC, FLAC (to 96kHz, 24-bits) and WAV (to 48kHz, 24-bits). But more of the tracks on my test USB stick were played than I expected, including some encoded in a number of formats that weren’t listed in the manual. Such as FLAC up to 24-bits and 192kHz sampling, and Apple Lossless in both CD standard and 24-bit, 96kHz.
It isn’t so much that this support provides super high fidelity sound, although the sound was fine. It’s a matter of convenience. If you have high resolution audio versions of tracks on your home storage, it’s a pain having to manage a separate set of down-sampled tracks just for the car.
The video formats supported are an array of codecs in Xvid, MPEG4, WMV and FLV containers, limited to modest bitrates and resolutions that don’t exceed standard definition standards. My test files looked about as good as one can expect on a small screen, especially viewed from an angle.
As for sound, the quality was first class, sounding as good as any head unit can. And that includes without the use of a subwoofer. On a wide range of rock music the unit exercised fine control over the bass, even down into the 40Hz region. You might run out of power with some systems, necessitating the addition of outboard amps, but you won’t lack for sheer quality.
The Sony XAV-AX100 is a fine implementation of both Android Auto and Apple CarPlay. If it also allowed time alignment and, as the cream on the already tasty cake, included a DAB+ tuner, it would be just about perfect. 
Sony XAV-AX100
Sony XAV-AX100 multimedia head unit
Price: $799
+ Apple CarPlay and Android Auto support
+ Good overall performance
+ Good screen and touch control

- No time alignment or analogue input

Type: Double-DIN head unit
Features: 163mm (6.4 inch) 800 by 480 pixel colour display, Bluetooth (hands-free/music streaming, mic supplied), AM/FM, USB for music/video, Apple CarPlay, Android Auto, remote control
Power: 4 x 55 watts into 4 ohms