Calyx PaT Portable USB DAC and Headphone Amplifier Review

Perceived Sound Quality and Final Thoughts

The Sound

I am personally a fan of high-quality digital music, and while I enjoy all-analog sound (my Music Matters Blue Note collection can speak for this) I am amazed at just how realistic well-recorded and mastered digital audio can be. Add to this the portability of such music with everything from an iPod (which supports uncompressed audio up to 16-bit/44.1 KHz) to a high-end digital audio player, and you have a match made in heaven. But there has always been a barrier to entry for high-end music on the go, with audiophile DAPs easily running $400 or more and by their nature used as standalone devices, requiring a user to carry a separate phone to stay connected on the go.

Once again it was the versatility of a product like the Calyx PaT had me so interested when I began, as it allows the use of one’s existing smartphone as the digital player. While external USB sound is nothing new for the PC, this is a very different concept for smartphones and one that I was skeptical about at first (as I have been using an Android phone as my primary device). While I expect Apple devices to function properly in this department given the endless number of compatible sound docks and ubiquitous support in modern cars, I had not previously experienced success with digital output from micro USB with Android phones, but as I previously mentioned this was a very different experience with the Nexus 6 running Android 5 Lollipop.

For consistency I created a small playlist of music from my library, and my initial impressions were all made using one of my favorites, Maiden Voyage by Herbie Hancock. This mid-1960s jazz album is an excellent test of digital fidelity as there is a lot going on, from complex drum work focused on the cymbols that challenges the speed and accuracy of treble reproduction, to the more spaciously recorded horns that reveal deficiencies in decay, and enough well-defined bass to round out what is a very complex form of music. Using the CD (or “redbook”) layer of the Analogue Productions SACD, I converted the CD to FLAC using JRiver using default settings and played it back with the excellent Onkyo HF app on Android and iOS, and used the JRiver software (and now standard WASAPI sound interface in Windows) for playback on my PC.

Digital and Analog

Digital audio is a very complex subject, but there is no mistaking good sound when we come across it, regardless of the source. While I won’t go into great detail on how a DAC works, I will say a few words about implementation. In the case of a digital-to-analog converter, certain choices have to be made about the reproduction of sound. One of these determines how long a particular sound is allowed to continue before being turned to zero, as essentially each frequency that the DAC is generating could be allowed to slowly fade away, or it could be sharply stopped, with an infinite amount of adjustment in-between. "Roll-off" is sometimes adjustable on a full-size component DAC, but in most cases we are relegated to the way it was tuned.

As a listener of analog music – with a collection of music that was recorded, mastered, and cut to vinyl using only analog tape – I can say that there is a different feel to analog, and some of that difference comes from the graceful decay of notes as they fade into the background. Subtle things like the echo of a note hitting the back of the recording studio and being picked up by another mic, or the intricate vibration of even a single acoustic guitar note as it drifts away can sound very different depending on how aggressively the D/A converter is handling roll-off. While this is a technical thing that I don't pretend to fully understand, I must say that I felt the sound from the PaT was more analog than that of the integrated DACs in the devices I tested, and part of this came from how natural the decay of notes seemed to be in my listening.

Now I'll cover my impressions from listening to the PaT on different platforms.

Android (Nexus 6, Onkyo HF Player)

The PaT connected to my Nexus 6 and iGrado headphones

Here is where my experience with the PaT began, and it was nothing short of a revelation. I have never been impressed with the audio output from the Nexus 6, as the headphone amplifer is quite weak and music sounded rather narrow and dull through any of the headphones I’d tried. There was never a chance that the button functionality would work with an Android phone, but this was fully expected going in and simply a limitation of the platform. So with my small selection of 16-bit/44.1 KHz FLAC music loaded up I put on my Grado “iGrado” headphones (Grado’s least expensive ‘phones at $49 – recently replaced by the new eGrado), which have excellent sensitivity and should be easily driven by the PaT's headphone amp. They were.

The iGrado is a slightly warm headphone already with a forward midrange in my experience, and though the PaT accentuated the warmth a bit the overall sound was well organized with the PaT controlling the (Grado SR60-based) drivers beautifully. But one of the biggest things I noticed almost immediately beyond the warm character and excellent detail retrieval was the width of the sound. With the Nexus 6 the PaT sounded very fast and articulate, with no “smearing” and an excellent sense of space around the instruments with the well-recorded music I sampled.

Even the best specs on a D/A converter are meaningless if it can’t reproduce something that sounds like real music, and with a device like the PaT there is the added complexity of the headphone amplification, which has the potential to muddy the sound if not well-implemented. Considering the huge improvement over the built-in audio from the Nexus 6 I was instantly impressed with what Calyx has done here. Gone was the narrow, dull sound that I’d grown accustomed to with this phone, and in its place was a wide, inviting soundstage with a far more detailed and realistic sound. Add to this the slight warmth of the PaT and you have a recipe for longer periods of fatigue-free listening.

iOS (iPad mini Retina, Onkyo HF Player, Apple Music, Pandora)

Audio is an area where I think Apple really got things right with iOS devices. There are countless docks and other audio accessories that work through not only the Lightning connection but their AirPlay wireless implementation, all of which offering very good control over audio playback. If your car has a USB port for its audio system, rest assured that an iPhone or iPod will be recognized and offer digital audio playback through the car’s controls. (This is sadly not the case for Android users, who are often relegated to using a 3.5 mm auxiliary cable – hardly an ideal solution.) As the PaT only offers a micro USB connection, support for Apple iOS devices requires a conversion from Lightning to USB. Fortunately this is quite simple courtesy of Apple’s “Lightning to USB Camera Adapter” which adds a full USB port to any current iOS device – and these adapters aren’t expensive at $29.

With an iPad mini Retina connected I tried out music from different applications, and the controls on the PaT worked flawlessly in each. I was controlling volume with the top and bottom buttons, skipping tracks with the left and right buttons, and toggling play/pause from the center. Sound was of course identical from iOS as Android, as it is the PaT converting and amplifying it regardless of the digital source.

PC (ThinkPad Yoga S1, Windows 8.1, JRiver Media Center 20)

Listening through the same FLAC selections on the PC I was again struck by the sound quality of this tiny DAC. Yes, I was listening to the same source material, but I spent more time on the PC as I was writing my impressions. After cycling through tracks (ranging from Bach cello suites to much more recent music from jazz trumpet player Ibrahim Maalouf's Wind), I again settled on my favorite jazz album, Maiden Voyage. Listening through "Little One" (track 3) I was again surprised at how much air and space around Tony Williams’ drums I could hear. The ringing of cymbals decayed with realism, highlighting the overall accuracy of treble I’d noted during my prior listening. Bass response was very good as well, and the slight warmth of the overall sound provided a relaxed sound and smooth midrange with a considerably wider soundstage compared to my ThinkPad’s audio as well. But the area where I was the most impressed on the PC? Those controls! Yes, the buttons on the PaT work with Windows exactly the same way as iOS.

While the sound is always going to be the most important part of any DAC (or music reproduction in general) I must talk about on the usefulness of the hardware controls on the PaT with a computer. Using my ThinkPad Yoga notebook running Windows 8.1 the PaT was immediately recognized as a USB DAC, and it was simple to set it up as my default playback device. I used JRiver Media Center 20 for music playback (with the now default WASAPI audio output) and controlled the experience with the PaT's buttons. With the PaT set to the default system device you can control volume, play/pause, and track skips in both directions, and this was not specific to the JRiver software.

Conclusion

The PaT provided a wide soundstage with warm, clear sound and excellent dynamics when using reasonably sensitive headphones. It retrieved greater detail than was possible using any of the onboard audio solutions I compared it against, and though solely bus-powered the PaT's headphone amplifier was more powerful than I expected. Not only was sound capable of being louder with greater clarity, but dynamics were not compressed the way I have grown used to with a mobile device. Loud passages had power, and soft passages had greater fidelity with lower background noise. The overall reproduction of digital music had a more realistic quality with greater detail and space than any of on-device audio I tried.

With its combination of excellent sound, low cost, and versatile application across PC and mobile devices, the Calyx PaT is a compelling product not only for the portable audiophile, but anyone who appreciates good sound. The PaT has a high level of fit and finish and great care has clearly been taken to tune the tiny device to levels of performance far beyond the price tag. Highly recommended.