Astell&Kern AK100 portable media player Page 2

My Sennheiser HD650 'phones have a nominal impedance of 220 ohms, which might suggest that they would be a much better match for the AK100. However, the downside of this high load impedance is reduced sensitivity: the AK100 couldn't drive the Sennheisers to anything like a loud enough level. With an impedance that varies between 70 and 95 ohms, the closed-back Sony MDR-7506 should work well with the AK100. Certainly, the AK100 had no problem driving the MDR-7506s to high levels.

Listening
I used the AK100 for six weeks of listening, mostly on the move but also for headphone listening at home. I performed all my initial auditioning using Ray Samuels Audio's Emmeline The Hornet headphone amplifier. This has an output impedance of less than an ohm, thus bypassing the impedance interaction issue. Even so, with the Sony MDR-7506 headphones playing "The Old Wild Men," from 10cc's Sheet Music (256kbps MP3 Amazon download, UK Records), I preferred the sound without the amplifier, the midrange sounding a bit better defined. Conversely, the Dunedin Consort's performance of J.S. Bach's St. Matthew Passion, conducted by John Butt (24/88.2 Studio Master download, Linn CKD 313P), benefited from the Emmeline's extra control of the bass, the direct sound lacking low-frequency authority.

With the Ultimate Ears 18 Pro driven direct, the treble of the St. Matthew Passion sounded a little shelved down, with a forward upper midrange, but the low frequencies sounded fuller than I was expecting from the 'phones' impedance curve. Driven by the Ray Samuels amplifier, the Ultimate Ears had a more even balance through the midrange and treble, with a tighter upper bass and more extended lower bass. Even so, I found that, in the long term, I wasn't bothered by the alteration in tonal balance with the in-ear monitors driven directly. It was akin to using tinted glasses—after a while, you're no longer aware of the tint. And it could be corrected with the AK100's built-in equalization, of course.

I was using the AK100-Hornet combination on a transatlantic flight when the battery in the amplifier gave up. (I hadn't recharged it before leaving for the airport.) I continued the journey with first the JH16s, then the Ultimate Ears connected directly to the AK100. There was still low bass present—the pedal lines in Bach's Prelude and Fugue in D, performed by Michael Murray on the organs of the First Congregational Church in Los Angeles (ALAC files, ripped from Telarc CD-80088), were still readily audible, but more so with the UE18 Pros. In "Love and Blessings," from Paul Simon's So Beautiful or So What (24/96 Apple Lossless file, Hear Music/HDtracks), the primary bass instrument in the verses is a deep-toned drum. But a descending bass-guitar line appears in the doo-wop bridge, and even without the Emmeline amplifier, this was well defined through the Ultimate Ears, and appropriately supportive of the melodic line.

By contrast, with the AK100 driving the Sony headphones, even with the theoretically better impedance match, that bass line was a little too lightweight. Contrary to what you can read on the Internet, the balanced-armature in-ear monitors did not have a problem with the AK100's 22 ohm output impedance, other than the modification of their frequency response. With most recordings, the Sonys needed the outboard amplifier to best serve the music, while the Sennheiser HD560s needed it simply to play loud enough.

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Now that's a problem
The majority of rock and jazz albums consist of individual songs, so if that's all the music you play, you wouldn't spot the AK100's shortcoming with many classical recordings: it doesn't offer gapless playback! This is not a problem with concertos and symphonies from the classical era, but with a recording like the Dunedin Consort's performance of Bach's St. Matthew Passion, not to mention any through-composed opera, where the track markers are dropped into a continuous stream of music, you end up with half-second silences between tracks where there should be none.

Against the 160GB iPod Classic
My iPod Classic is 2010 vintage and has a measured output impedance of 5 ohms. The first comparisons were with each player connected to the Emmeline headphone amplifier driving the Sony MDR-7506 headphones. Obviously, as the iPod is limited to sample rates of 48kHz and below, all comparisons were performed using files ripped from CD or downloads at 44.1kHz.

Playing 10cc's "Old Wild Men," it was no contest. The iPod had a more aggressive mid-treble, the AK100 more refined-sounding highs with more top-octave air. It was a close match when it came to the amount and quality of low frequencies, but overall, the lossy compression seemed to have more of a damaging effect with the file played on the iPod. There was consistently more of a sense of ease with the AK100.

There was less space apparent with the iPod when I played "Fit Song," from Cornelius's Sensuous (ALAC files ripped from CD, Warner Japan EVE016). Perhaps more important, both the drum samples and the staccato guitar chords on this track had more texture through the Astell&Kern, sounding less like shaped and processed noise. The iPod wasn't unlistenable, but it tended to emphasize the rattle of the snare wires; the AK100 let me hear a little more of the body of the snare drum's sound.

In the Big Rig
I finished my auditioning using the AK100 as a standalone DAC in my reference system. I used AudioQuest's top-model Angel stereo 3.5mm-to-RCA cables to connect it to the preamp, though it's fair to note that, at $865, this cable is significantly more expensive than the player! But before auditioning the Astell&Kern as a DAC, I used a Monster TosLink 3.5mm optical cable to connect its S/PDIF output to the Arcam FMJ D33 DAC, so I could get a handle on its performance as a data source.

It performed very well in this role. Joni Mitchell's "The Jungle Line," from Herbie Hancock's River: The Joni Letters (Apple Lossless 24/96, Verve/HDtracks), fed to the Arcam DAC from the AK100 via TosLink, sounded indistinguishable from the same file fed from my Mac mini to the Arcam via USB. And to my surprise, the AK100 did output 192kHz-sampled data via TosLink.

Feeding analog data from the Astell&Kern to the Pass Labs preamp and comparing with the Arcam with levels matched at 1kHz, the high-end DAC offered a better-defined soundstage, with more precise sculpting of the individual objects within the recorded space. The AK100 sounded a little less involving, with a flatter soundstage overall. But considering the price, the AK100 served well in this role, sounding close to the budget-priced Schiit Bifrost reviewed elsewhere in this issue. The Bifrost reproduced more of the overwarm double bass in "Killing the Blues," from Alison Kraus and Robert Plant's Raising Sand (24/96 ALAC file transcoded from FLAC download, Rounder/HDtracks 11661); the AK100 offered better definition of the bass. It also had a little more top-octave air apparent than the soft-sounding Bifrost.

Astell&Kern's AK100 is a true high-end source component.

Summing up
Given that in-ear headphones, especially those that use a single armature, roll off in the top octave, a skeptic might argue that there is little point in a portable player offering the capability of handling files sampled at greater than 48kHz. And when you consider that an old guy like myself, just turned 65 as you read these words, can't hear frequencies above 14kHz, the case against high-resolution portable playback would appear to be closed. Yet my experience of music sampled at 88.2kHz and above through the Astell&Kern AK100 was positive; versions of those files downsampled to 44.1kHz sounded less involving, and grayer overall. Case proven for the higher sample rates and bit depths, as far as I'm concerned.

What is incontrovertible is that the AK100 offers listeners on the move a better-performing and -sounding DAC than that used in the iPods. If you can live with the lack of gapless playback, I highly recommend this first offering from Astell&Kern (footnote 1). At $699, it's reasonably priced for what it offers.



Footnote 1: At the High End show in Munich last May, Astell&Kern announced their second product. The AK120's D/A and analog circuits are dual-mono, it supports up to 192GB of memory, and offers gapless playback, all for a significantly higher price than the AK100: $1299. The AK120 will be available in the US in the fourth quarter of 2013. A&K says that a firmware update for the AK100 will add gapless playback.
COMPANY INFO
Astell&Kern, Korea
US distributor: iRiver Inc.
39 Peters Canyon Road
Irvine, CA 92606
(949) 336-4540
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COMMENTS
gld3gld3's picture

"Ten years later, while the current top-model iPod features a 160GB hard drive, it still can play only files with sample rates of 48kHz and below and a maximum bit depth of 16. Those of us with a growing library of high-resolution files are therefore restricted to playing them in our big rigs at home."

Not exactly. There is at least one option for those wanting to play higher sample rate/higher bit depth files on their ipods.

My 5th gen ipod is currently playing "Happlessness Blues" by Fleet Foxes at  sample rates of 96kHz  and bit depth of 24 (FLAC). How? Rockbox. 

John Atkinson's picture

gld3gld3 wrote:
My 5th gen ipod is currently playing "Happlessness Blues" by Fleet Foxes at  sample rates of 96kHz  and bit depth of 24 (FLAC). How? Rockbox.

Rockbox does indeed add a lot of functionality to iPods (and other portable players). However, it can't overcome the hardware limitations of the player. Even if you can play a 24/96 files, as you report, the iPod's DAC chip is limited to sample rates of 48kHz and below, so the file will be downsampled.

In additon, while Apple's AAC and Lossless codes will preserve 24-bit resolution, the iPod's DAC is a 16-bit part, so will truncate the word length by the 8 LSBs. For example, if you look at the spectrum at www.stereophile.com/content/ipod-classic-160gb-1khz-90dbfs-16-bit, this shows my 2010 iPod Classic playing a dithered 16-bit tone at -90dBFS. Everything is correct, and the noisefloor is free from harmonic spuriae.

By contrast, the spectrum at www.stereophile.com/content/ipod-classic-160gb-1khz-90dbfs-24-bit shows what happens when the iPod plays back a 24-bit dithered tone at the same level encoded with the ALAC codec. The appearance of the odd-order harmonics is due to truncation of the 24 bits to 16.

So yes, it may be possible to play 24/96 files on this iPod running the Rockbox software, but the file will be downsampled and truncated. The AK100 doesn't suffer from these hardware limitations.

John Atkinson
Editor, Stereophile

jcborges's picture

How were your measurements of the iPod taken? I ask because looking at the specs of the iPod DAC at http://cirrus.com/en/products/cs42l55.html it is definitely capable of 24-bit, although it is limited to 48khz sampling frequency.

Why would Apple put a 24-bit capable DAC in the iPod and have it truncate to 16? And how could it be done? And couldn't Rockbox bypass that to access the full bit depth available on the chipset?

Thanks and regards

John Atkinson's picture

jcborges wrote:
How were your measurements of the iPod taken? I ask because looking at the specs of the iPod DAC at http://cirrus.com/en/products/cs42l55.html it is definitely capable of 24-bit, although it is limited to 48khz sampling frequency.

I took a 24-bit AIFF file representing a dithered 1kHz tone at -90dBFS and prepared from it WAV, ALAC, and AAC at 320kbps files. The WAV file wouldn't play in either my iPod Classic 160GB or my iPhone 3GS, but from the other three versions I expected to get a spectrum that looked like the red and blue traces in fig.5 at www.stereophile.com/content/astellampkern-ak100-portable-media-player-measurements.

Instead, from both players and with AIFF, ALAC, and AAC versions of the data, I got the spectrum shown at www.stereophile.com/content/ipod-classic-160gb-1khz-90dbfs-24-bit. The characteristic pattern of odd-order harmonics indicates truncation of the 24-bit data to 16. By contrast, the AK100 playing both the AIFF and ALAC versions of the data gave the correct spectrum shown in the review.

jcborges wrote:
Why would Apple put a 24-bit capable DAC in the iPod and have it truncate to 16?

I have no idea. This was not what I was expecting, as the new "Mastered for iPod" protocol recommends using a 24-bit master to prepare the AAC version, which in turn implies a 24-bit datapath..

jcborges wrote:
And how could it be done? And couldn't Rockbox bypass that to access the full bit depth available on the chipset?

That is possible, but as you point out, the chipset is still restricted to sample rates of 48kHz and below, contrary to what the original poster claimed.

John Atkinson
Editor, Stereophile

jcborges's picture

First, thanks a lot for your answers. But you left me wondering about something. 

If understood correctly, your measurements were made in the analog domain. What about digital?

If you play a 24bit/48khz ALAC file through a digital dock, what is the format of the PCM stream that comes out? 24-bit or 16-bit truncated? Have you ever checked or know someone who has, for example by connecting it do a DAC that shows the input format?

In the other words, if you have 24/96 files that you want to put in an iPod to playback digitally, should you just resample them to 48khz or should you apply TPDF dither to avoid truncation? Does it matter? 

 Thanks and regards

John Atkinson's picture

jcborges wrote:
If you play a 24bit/48khz ALAC file through a digital dock, what is the format of the PCM stream that comes out? 24-bit or 16-bit truncated?

If you play a 24-bit AIF or WAV file, the AK-100's digital port outputs 24-bit data. But I will check with ALAC data.

John Atkinson

Editor, Stereophile

John Atkinson's picture

John Atkinson wrote:
jcborges wrote:
If you play a 24bit/48khz ALAC file through a digital dock, what is the format of the PCM stream that comes out? 24-bit or 16-bit truncated?
If you play a 24-bit AIF or WAV file, the AK-100's digital port outputs 24-bit data. But I will check with ALAC data.

Okay, played back a dithered 24-bit 1kHz tone at -90dBFS, encoded both as AIFF data and as ALAC data. In both cases, all 24 bits were active in the AK100's optical output and the digital-domain spectra of the two codecs were identical, with a noisefloor at the 24-bit level.

So the answer to your question is yes, when the AK100 plays a 24-bit ALAC file, the digital output is true 24-bit as it should be.

John Atkinson

Editor, Stereophile

JohnnyR's picture

*eyeroll*

So having a player that has crappy high output impedance and doesn't have gapless playback is a good thing? For the money I would expect a lot better. What's wrong with using FLAC in other players that cost less and have gapless playback to boot?

Another laughable product that Atkinson likes.cheeky

John Atkinson's picture

JohnnyR wrote:
So having a player that has crappy high output impedance and doesn't have gapless playback is a good thing?

As I wrote, the most recent firmware upgrade allows gapless playback. I examined the effect of the 22 ohm output impedance at length in my review - "crappy" is a mischaracterization of the relatively small changes in frequency response that result from this impedance, especially when you consider that many headphones and in-ear monitors have boosted low frequencies.

John Atkinson

Editor, Stereophile

JohnnyR's picture

For $699 you should get a lot better response and features. Sorry but changes from 1 to 2 dB would be scandalous in a preamp or power amp but since it's this THING then it's "okay". oh brother.blush Seriously, lower priced players don't have this problem so it's a FLAW easily avoided if they had designed it right.

ChrisS's picture

Comrade,

There must be something about your Stalinist upbringing that makes you believe that the perfect audio product exists somewhere out there, when really that kind of perfection only exists in your imagination.

Di Keller's picture

I bought one of these today on impulse. It just sounded sooo good. Got it home and it is not that mac friendly. The big problem is being able to upgrade the version so it will be gapless. It is done via Iriver Plus 4 for pc. But I haven't been able to find a firmware update for mac. Iriver really don't seem to like us :(

John Atkinson's picture
Di Keller wrote:
The big problem is being able to upgrade the version so it will be gapless. It is done via Iriver Plus 4 for pc. But I haven't been able to find a firmware update for mac.

You don't need the iRiver PC app. You connect the AK100 to the Mac using the USB drive option. After downloading the new firmware from the A&K site - it will be called AK100.hex - you copy it into the AK100's root/system directory. (Make sure that your AK100’s battery level is at least over 80% and make sure of your AK100’s memory size is at least 50MB.) When you reboot the AK100, it will automatically install the new firmware.

John Atkinson
Editor, Stereophile

Di Keller's picture

^^ Firstly thanks for answering so promptly. I found the A&K site I have figured out how to do it. But the problem is finding a link for the firmware that works. I keep getting zip files which won't unzip. Or are incomplete.

Di Keller's picture

Just tried again and finally got it. Thank you for your help. !!

John Atkinson's picture
Di Keller wrote:
Just tried again and finally got it.

I remember having to try downloading the new firmware several times before it worked.

Di Keller wrote:
Thank you for your help. !!

You're welcome. Enjoy your music on the AK100.

John Atkinson
Editor, Stereophile

Di Keller's picture

Finally all set up.!! Had all sorts of problems installing the upgrade. Followed everything to the letter and it just didn't work. I went back to the place I bought it from. They tried it and it didn't work. The answer was really simple in the end. We were all putting the hex file into the system file , if you just dropped into the AK100 folder it worked out the rest it self. Good news, while I was there they put a $6500 pair of headphones on me, If I was religious I would have said it was a religious experience . Hahahaha!! The sound was amazing !! I could feel my face crumpling. :)

Björn-Ola's picture

My Ak100 plays happily from 128GB cards. Just format them to FAt32, and it works splendidly.
I also think that the new firmware 2.40 changed the sound a little bit to the better, but it could be my imagination.

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