New angles

Astell&Kern’s latest high-res portable brings the brand into competition with cheaper rivals. So what have they left out?

It looks like Astell&Kern is going affordable. Well, a little bit anyway. Rather than a portable media player priced at $5000+, this Astell&Kern SR15 is available in Australia for $999. Its full name is the ‘A&norma SR15’, presumably to contrast it more completely with the more expensive A&futura SE100.

Equipment
The A&norma SR15 is a smallish (10cm long) high-resolution music player. It has 64GB of storage built in, and supports a single SD card of up to 400GB for additional storage. It has a 3.5mm stereo output for regular headphones, and a 4-pole 2.5mm output for balanced headphones.

Also built-in is Bluetooth, with support for the relatively high quality aptX HD codec (this is backwards-compatible with headphones which support only aptX) and Wi-Fi for things like firmware updates, and music downloads.

There’s an 84mm touch screen, placed on the front at a funky angle. This is about as sensitive and easy to use as a typical phone, apart from being rather smaller than the norm. On the right hand side is a rotary volume control. At the top there’s a power button. On the left are small buttons for skip forwards, skip backwards and play/pause.

The SR15 uses dual Cirrus Logic CS43198 DAC chips. It supports up to 24-bit/192kHz, PCM (and variants in various losslessly compressed formats) and DSD64 natively. It will also play 352.8 and 384kHz content, but scales them down to 176.4 and 192kHz. Likewise, it’ll handle DSD128, but converts this to 176.4kHz PCM for decoding. Don’t like that? Its Micro-B USB port — generally used for charging and transfer of music — also supports the On-The-Go standard, so you can plug in an external DAC.

Running things inside is a heavily customised version of Android. It’s locked down, so it doesn’t really look like Android; indeed, the usual soft keys at the bottom of the screen aren’t there.

I measured the weight of the unit at 160.5 grams with a microSD card installed. As seems to be common with this kind of player, there are plenty of sharp corners.

Listening
I did much of my listening with my pair of 20-year-old Sennheiser HD 535 open-back, over-ear headphones. I went for quite a few years not using these for a number of reasons, not least because they are quite fussy about the source. They need a source capable of delivering a firm, powerful bass, and indeed a fairly high level across the frequency spectrum, thanks in part to their quite low sensitivity.

I found listening to music using these headphones and the SR15 a delight. Their tendency to a lightweight sound was eliminated by the SR15. It took masterful control over them, and showed their audio reproduction in its best light, the sound becoming open, airy and clean, with a deep if slightly recessed bass. Even Eminem’s ‘The Slim Shady LP’ sounded balanced, with the driving bass fully compelling.

Importantly, regardless of what I played, the output level of the Astell & Kern SR15 was easily sufficient to drive them to thrillingly high levels, with a little in reserve in case I was tempted to go even higher. You are unlikely to find any main stream headphones, let alone earphones, these days which are of lower sensitivity than the HD 535s.

Results were less successful with a set of Sennheiser Momentum In-Ear earbuds. These $170 models are inclined towards a very bright treble, and the SR15 could do nothing about that. I’m not sure anything could.

So, onto my Oppo PM-3 planar headphones. They brought up the bass that had been recessed with the HD 535 headphones, while more or less retaining balance. I enjoyed the first Dire Straits album, held on the SR15 in DSD format. There was superb detail and an impressive driving quality.

I moved over to what used to be my favourite Beethoven piano sonata album: Vladimir Ashkenazy, playing the 8th, 14th and 23rd on Decca. I remained disappointed. This is a wonderful rendition through speakers, but has never been satisfying through headphones. (Even Sennheiser’s recent very expensive HD 820.) I tried again, futilely hoping something will make it sound good through headgear. It didn’t.

I even switched headphones again, this time to the Blue Lola, a set which look ungainly but sound quite impressive for their $450-ish price. Still poor. Not poor was Roxy Music’s debut self-titled album. (I know Bryan Ferry doesn’t like the mix, but I do.) There was first-class impact, excellent balance, and a gloriously layered sense of space.

Measurements
There is no dedicated line output as such on the SR15, but it doesn’t really matter because there’s a ‘line out’ mode using the regular headphone socket. You enable this in the settings menu and choose the preferred level — 0.7 volts, 1 volt, 1.25 volt and 2 volts are available. Then when you change the volume using the knob, a line out button appears on the screen (in addition to the volume changing normally). Tap the button and the SR15 switches to fixed output mode. (Why those levels? I don’t know. There are intervals of 3dB, 2dB and 4dB between the pairs above.) I measured the line output with the 2 volt setting into a 47.1kHz load, and it came to 2.01 and 1.99 volts RMS for the two channels according to my oscilloscope. In other words, spot on the claim. (Even if the slight divergence is in the unit rather than my measuring rig, it amounts to less than 0.05dB.)

Setting the unit to headphone output mode, playing the same 0dBFS 1kHz sine wave into the same load, with the volume control set to 150 — the maximum — the result was identical. I’m guessing all the line output setting does is fix the output level. In other words, it’s a convenience for use with other audio systems.

Switching from the 47.1kHz load to 295 ohms, there was no clipping even at maximum output, and just about no reduction in output (only in the third significant figure, from 2.01 to 2.00 volts). Into a 15.9-ohm load there was massive clipping. I turned the level from the maximum of 150 down to 130 to eliminate it. You can safely say that playing into just about any headphones at an indicated 130 will guarantee no clipping (although it may well guarantee ear damage!). The output was still 0.565 volts, which is 20 milliwatts into that load. And that works out to 13dB above the sensitivity rating of whatever headphones you’re using.

Switching the load back to open circuit while retaining the same volume level, the output increased to 0.637 volts. From that it was easy enough to calculate an effective internal resistance of pretty much spot on 2 ohms. Perhaps a touch higher than with other high quality portable players, but still sufficiently low that it should result in no frequency response anomalies in any headphones with varying impedances across the audio band.

Sadly, the software I have been using in recent years to conduct other measurements simply refuses to work any more on any of my computers. That means I cannot measure signal-to-noise ratio or distortion, but I’d note that to the extent there is any noise or distortion created by the SR15 (as there must be), it is below any audible levels.

I went old-school on measuring frequency response (above), using pink noise signals and filtering them after recording to remove the 3dB per octave tilt. For 44.1kHz sampling, there’s a straightforward clinical treatment: flat to 20kHz and a sharp filter thereafter. For 96kHz sampling, the treatment is much the same, except that it was flat to 42kHz. The same pattern probably repeated for 192kHz, except that my ADC was softening the curve at the top end. Even then it was flat to 56kHz and down 3dB at 80kHz.

Those who swear by slow, gentle filters are likely to be disappointed. The rest of us can be confident that whatever is up there in the high frequencies, or indeed, suprasonic frequencies, is being delivered.

Practicalities
Using the player was easy in general. It took me a moment to discover that when something’s playing you can tap on the cover art to bring up additional controls, such as repeat and random. And this also brings up an arrow so you can back out through the music access ‘tree’ the way that you came in.

Meanwhile, a swipe from the top gives access to the Android-y features, a swipe from the right opens the playlist, and a swipe from the left opens the main menu.

But most importantly, the skip and play/pause controls and rotating volume control all work when the display is asleep. No need to waste power on that so long as you’ve got stuff in your playlist.

I tried the in-line play/pause controls on headphone designed for iPhones and for Android phones, and neither worked. That’s a pity since they are so ubiquitous.

Finally, one weakness of so completely customising and locking down the Android system is that other music player software can’t be used. There’s nothing wrong with the one provided, but, say, as a keen podcast listener, I would have liked to be able to put a podcast app on this unit and make it my all-in-one everything player.

That said, Astell&Kern says that new firmware will be provided with the new A&ultima SP1000M (one up from the A&futura SE100 player) that permits the manual installation of apps in the form of Android APKs. Maybe that feature will trickle down into this model. (Maybe not.)

Conclusion
The Astell&Kern SR15 is a nifty little high definition portable player. It sounds great, is highly usable and has plenty of capacity if you buy a suitable card. 

Astell&Kern A&norma SR15
Price: $999

+ Good value
+ Very solid performance
+ Plenty of storage

- Lacks flexibility of some
- Play/pause in-line controls on headphone cords didn’t work

Tested with firmware: version 1.04
Display: 84mm colour touch-screen, 480 x 800 pixels
Storage: 64GB internal, 1 x microSD slot (up to 400GB)
Outputs: 1 x 3.5mm headphone/line/optical digital audio, 1 x 2.5mm TRRS for balanced headphone/line, Bluetooth
Other: 1 x USB Micro-B, Wi-Fi
Dimensions (whd): 57.5 x 99.7 x 16.1mm
Weight: 154 grams