Published On: May 6, 2015

Calyx M Hi-Res Music Player Reviewed

Published On: May 6, 2015
Last Updated on: October 31, 2020
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Calyx M Hi-Res Music Player Reviewed

Steven Stone reviews the $999 Calyx M hi-res portable audio player to see how it compares with competing models from the likes of Sony and Astell & Kern.

Calyx M Hi-Res Music Player Reviewed

  • Steven Stone is the former editor of He a longtime audiophile and home theater writer, as well as a musician and recording engineer. Steven has written for publications like Stereophile, as well as,, and The Absolute Sound.
    Steven is plays guitar, mandolin, and Ashbory bass and is a collector of fine musical instruments.

Calyx-M.jpgHigh-performance portable audio is the fastest-growing segment in consumer audio. The reason is pretty obvious: our more mobile society. The big trend that has accompanied this is streaming, which keeps your music library "up in the cloud," accessible by virtually any Internet-savvy portable device. But what about those music lovers whose musical interests are more focused and not well served by streaming services created more for popular tastes? For those who like to keep their music libraries more earthbound, companies like FIIO, Astell & Kern, HiFiMan, Sony, and iBasso have produced portable players that let users take their libraries with them when they travel. One of the new companies entering into this portable player cornucopia is Calyx. This Korean brand has made waves with its highly regarded listening-room-bound Femto DAC. The new Calyx M player attempts to bring that same level of audio sound quality to the portable realm.

I've had the Calyx M in my possession for four months. Usually I don't take this long with a product under review, but the M was an exception, due to several factors. The first was that, when I originally received the M, it was running on a much earlier firmware version. Since it arrived, I've updated the Calyx M firmware three times. Each update has increased the M's functionality, battery life, and stability. This firmware is, in the words of Calyx's CEO Dr. Seungmok Yi, "the one we originally planned." I'm glad I waited until v1.01 to review the M because it takes the operating system from good but slightly primitive to great. Also, since Calyx is a relatively new manufacturer, I wanted to make sure that the M was reliable and supported with the same level of vigor in the United States as premium players from other manufacturers. The final reason for the delay was personal: I was in the process of moving to a new home, and it's hard for me to write with no office to write in. Now I'm confident that the Calyx M has become a serious contender in the $1,000 price range--ready to compete with the Sony NW-ZX2 and Astell & Kern AK100 II.

Product Description
Unlike many players whose designers felt the need to shape them in a unique way, the Calyx is basically smartphone-shaped. It measures approximately 5.25 by 2.75 by slightly more than 0.5 inches, and its 1,280 by 720, 4 by 2.25-inch OLED touchscreen display covers most of the front panel. On the top, you'll find a mini-stereo headphone connection next to two smartcard slots: one for full-sized cards and a second one for micro-SD cards. To the left of the card slots is a push button that serves as the on/off and sleep/wake-up control. The right side of the player is populated by a large sliding volume control and three buttons for reverse, play/pause, and skip forward. The bottom of the player has a mini USB connection.

According to Calyx, the operating system used for the M is from Muse UI, which is an Android-based interface. It doesn't look anything like an Android phone, and it isn't an open system like the Sony NW-ZX2 where you can add third-party apps from the Android store. Firmware updates proved to be relatively easy; merely load a download from the Calyx website onto a smartcard's root directory, put it into the Calyx, go to the firmware update page in settings, and let the M do the rest, including unzipping the file.

The Calyx M can function as either a standalone portable player or a USB DAC. Its core processor is a Cortex A5 ARM chip with one gigabyte of internal memory. A Sabre ES9018-2M serves as the DAC chipset. The M supports FLAC, WAV, DFF/DSF (64DSD and128DSD-DoP), DXD, AAC, MP3, MP4, M4A, and OGG formats. The player is able to play files up to 32-bit depth and do sample rates of 44.1, 48, 88.2, 196, 76.4, 192, 352.8, and 384.

Like many players, the Calyx M has a non-user-replaceable 3100 mA battery. Battery life with the Calyx M has been a moving target; the earliest OS did not deliver the same battery life as v1.01. With the latest firmware and reasonably efficient headphones, the Calyx is averaging between five and six hours of playing time between charges. With less-efficient headphones, battery life can drop to under five hours. For anyone who is considering a player for use on long flights, the M will need the addition of an external battery pack to deliver music for the entire trip.

The Calyx M comes with a micro USB 2.0 cable and a soft cloth case. If you plan to carry the M around a lot, I recommend acquiring something more protective than the supplied case, which protects the display from scratches and fingerprints but will do nothing to shield the M from blunt-force trauma. Perhaps Calyx will make a hard leather protective case available in the near future.

Ergonomic Impressions
Unlike many shelf-bound audio components where somewhat kludgy ergonomic solutions can be tolerated for the sake of high fidelity, portable players need to be as functionally elegant as possible. Quirkiness is not a desirable trait. During the time I've had the Calyx M in my possession, it has proved to be reliable and not prone to any major functional issues.

To turn on the M, all you need to do is hold down the button on the top for four seconds. You will be greeted by the Calyx C-Clef logo; then, after about 30 seconds, the M's home screen will appear, which contains the play, pause, skip, and fast-forward controls, plus track info. The track info includes the resolution of the file being played, format, memory used, the year the track was created, genre, composer, performer, and the album title. A sideswipe to the left brings you to the Calyx M's library, which lists all the tracks alphabetically on the M, by either album, artist, track name, or playlist. A sideswipe to the right brings up the M's jukebox page, which lets you build, edit, and save playlists.

The Calyx M's settings are accessed via a three-dot graphic in the upper left corner of the central play screen. There you will find options for impedance matching: low, medium, and high. Also in the setting menu are options for locking the screen and hardware buttons, gapless playback, screen sleep options, date and time settings, language options, library menu configurations, rescanning files, volume control options, system info (including firmware updates), and a universal system reset.

The impedance-matching adjustment does not actually change the M's output impedance, which is between zero and 0.5 ohms, but it does change the amount of gain the M can produce. The high-impedance setting provides the most gain, while the low-impedance has the least amount of gain. The other unusual control is the volume control: it puts a virtual volume control on your touchscreen in lieu of the physical slider. What it does not do is change the volume control's attenuation methodology. I tried it, but I preferred the tactile feel of the M's physical sliding volume control far more.

The Calyx M can drive a wide variety of headphones. Sensitive in-ears like the Westone ES-5 and Jerry Harvey Roxannes were dead quiet, with no background hiss or noise. With less-efficient full-sized headphones such as the Mr. Speakers Alpha Prime and the HiFiMan HE-560, the M still had enough power to drive them to satisfying levels. Even with my own live concert recordings, which are about 10 dB lower in average output than standard commercial releases to allow for the dynamic peaks, the M had enough juice to drive every headphone I use to satisfying volume levels. With my worst-case-scenario headphones, the Beyer-Dynamic DT990 600-ohm version, the Calyx M still had enough output to drive them past satisfying levels with commercial releases and to just about reference levels on my own recordings.

The Calyx can also be attached to a computer via its micro USB cable and used as a digital-to-analog converter (DAC). I connected its headphone output to the analog input on the NuPrime DAC 10H (this input remains analog, with no A/D and D/A in the circuit) and found that the Calyx's sonic performance was on par with the NuPrime's internal USB DAC. The Calyx M was as quiet as the NuPrime, even with the disadvantage of a meter of cable and an adapter in the way. Both USB DACs displayed equal levels of detail, dynamic acuity, and spatial precision. The potential problem of using the Calyx M as a USB DAC is the issue of battery life; however, while acting as a DAC, the Calyx can recharge. So, even after a full day of playing attached to the computer, it will be ready for an evening trip to the city.

Many high-resolution players, including the Sony NW-ZX2 and Astell & Kern AK 100 II, have built-in equalization adjustments. The Calyx M does not have any built-in EQ; so, if that is something you use often or rely on to correct for headphones or source material, you will not have that option with the current generation of M firmware.

Calyx-M-side.jpgSonic Impressions
During the past year, consumers' options in high-resolution players have expanded exponentially--with Pono, Sony, and Astell & Kern all introducing outstanding new models. But none of the aforementioned manufacturers have come up with a player that has quite the same set of features and sonic attributes as the Calyx M. The M ranks as the most flexible (in terms of successfully supporting the widest variety of earphones); and, to my ears, it is also the most natural and un-hifi-like of all the players I've heard.

One problem with trying to compare the sound of different players is that putting together an A/B test where levels can be critically and repeatedly matched is difficult. Also the lag time switching between players makes it hard to discern subtle differences between sonic presentations. That said, I did quite a bit of back and forth between the Calyx M and the new Sony NW-ZX2 and found that the sonic differences between the players weren't as great as the differences between various reference headphones I used.

With my most difficult-to-drive cans, the Beyer-Dynamic DT990 600-ohm version, the Calyx M demonstrated how its extra output capacity could make the difference between "loud enough" and "not loud enough." However, with easier-to-drive cans like the new Oppo PM-3 headphones, the differences between the Sony and the Calyx were subtle and, with anything less than excellent and familiar recordings, difficult to identify. The M sounds ever so slightly more relaxed, especially during dense passages, than the Sony. But the Sony has the ability to unravel these same dense passages in a slightly more lucid manner than the M.

Both the Sony NW-ZX2 and Calyx M had excellent bass definition, especially in the midbass, which often suffers from congestion and too much "thickness" on lesser players. Even on especially bass-centric tracks, the Calyx never got overwhelmed while handling bodacious bass. The Grado RS-1 headphones--which are fairly sensitive and easy to drive and do need a beefy headphone amplifier to sound their best, especially in the lower registers--sounded excellent tethered to the Calyx M. Bass was well-controlled with adequate visceral impact, which is not the case when I hooked up the Grados to my iPod.

Overall I found nothing to criticize about the M's intrinsic sonics. Like the Astell & Kern AK240 and Sony NW-ZX2, the Calyx M will not be the weak link in your portable system--no, that honor will fall to your headphones or the quality of your music files.

High Points
• The Calyx M sounds wonderful.
• It has slots for both micro- and standard-sized SD cards.
• It can drive a wide variety of headphones from high to low sensitivity.

Low Points
• Calyx M's battery life is limited to five or six hours. For long trips you will need to carry additional external power supplies.
• The M does not have any built-in EQ functions.
• The M does not support streaming.

Comparison and Competition
Competition in the under-$1,200 premium portable player category is stiff. Astell & Kern has one model, the AK100 II ($799), and Sony has the new NW-ZX2 ($1,199). Both can produce stellar sonics, and determining which is the best-sounding depends on several factors, including what headphones you prefer, what kind of music you listen to most, and finally what features are most important to you. If you use the Mr. Speakers Alpha Prime headphones with the Sony, you will find that, even when the volume is cranked to max, the overall volume isn't quite enough to push the Alpha Primes to what I would call "loud." The Astell & Kern AK100 II has a similar limitation when driving higher-impedance low-sensitivity headphones.

The Calyx is the best option if you favor difficult-to-drive and low-sensitivity headphones since it has a more powerful headphone amplifier than the other players. But if streaming is a critical feature for you, the Calyx will be less desirable than the Sony or A&K 100 II, both of which offer streaming options. Of the three, the Sony NW-ZX2 is the most fully featured because it can run any Android app from the play store.

Storage on the Calyx M outpoints the competition because it supports both micro and standard SD cards and has a slot for each. You can have one 128GB micro SD card and one 256GB standard SD card in addition to the M's 64GB of internal memory. The Sony NW-ZX2 has larger internal memory, but only accepts micro SD cards, which are currently limited to a max capacity of 128GB. The Astell & Kern has only 64GB of internal memory and also accepts only micro SD cards for a maximum capacity of 192GB.

Since Apple decided to discontinue its iPod classic, folks have been paying a lot more for iPods on eBay, sometimes as much as $450 for a mint 160GB seventh-generation version. While the Calyx M will still run you twice the cost of a used iPod, it will also deliver much higher quality sound due to its superior electronics and ability to play high-resolution files. Also, it's currently in-production and will be supported by its manufacturer for years to come, which will not be the case for any iPod.

If you are ready for an outstanding portable player and don't need or want streaming or the ability to run third-party apps, the Calyx M could be your best option in a great-sounding, high-resolution-capable portable player.

Additional Resources
• Check out our Media Servers and MP3 Players category page for similar reviews.
• Visit the Calyx website for more product information.

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