Acoustic Research AR-M2 The march of high-quality digital music continues. Since I last covered the subject, the UK version of the digital downloads site HDtracks has launched, with a cool, simple interface and 24-bit recordings of a growing number of albums for between £8 and £20. There’s also talk of my favourite “high-res” streaming site – Tidal – offering downloads at some point. Now be aware that 24-bit – the highest recording quality achievable – is controversial; there are plenty who say its above-CD sound quality is wasted on human ears. I disagree. If you concentrate on music and have decent hearing, you should find 24-bit recordings perceptibly clearer and more natural. It’s a small measure of improvement, but so is the difference between good and superb in any field. Once you start the delightfully Sisyphean task of re-downloading your entire music library, you will also need a player much better than a phone or tablet to listen to it. The gorgeous Astell & Kern AK240 that I featured here last year sets the benchmark; but this, the slightly bigger (but roughly half the price) new AR-M2 from Hong Kongbased Acoustic Research, is a serious competitor. It may look exactly like a mobile phone, and even has an Android operating system that means you can use it to do Android phone stuff – play games, surf the web – everything apart from actually calling people. But the real use for that expansive 5in screen is to display the controls and album covers in a way that’s both striking and easy to access. It’s also no exaggeration to say that the AR-M2 is a pocket-sized hifi system. Its sophisticated amplification can drive serious, audiophile over-ear headphones in stunning quality, which is notthe case with all portable players, and you can also wire it straight into a proper hifi. The only downside is that for portable use – where streaming music isn’t an option – the internal memory is just 64GB compared to the A&K player’s 256GB. You can, however, plug in a MicroSDXC card, which will currently provide up to 200GB of storage – allowing you to carry a great deal of HD music in your pocket. £899, from www.acoustic-research.com.