DAC Reviews

Virtual Reference Monitoring
I'm always intrigued when I see a pro-audio oriented company make products that have crossover appeal. There's some nice equipment out there from Benchmark, Grace Design, Apogee, Lavry, Antelope, etc which have become well known in the audiophile sphere. Others such as Lake People aren't quite household names yet, despite having been around since the 1980s. Most of these companies make a wide range of products but we tend to hear only about their DAC or headphone amp units because those are most relevant to our uses.

Another such company is Focusrite, which has also been around for several decades. Most of their catalog is pro gear such as microphone preamps or rack-mount audio interfaces with multiple inputs/outputs and knobs all over the place. One item of theirs did catch my eye though: the VRM Box USB interface (MSRP $149, street price $99). Rather than a wall of dials and jacks, we get a single volume knob, USB and SPDIF inputs, and a headphone jack. That's it. The unit couldn't be simpler and couldn't be more different from their other equipment.

If the VRM Box stopped there it would be only mildly interesting, since there are plenty of compact USB DAC/headphone amp units on the market. What makes this device unique is the Virtual Reference Monitoring feature. Using special software, it can supposedly emulate the sound of various speakers in various rooms, all through your standard headphones. It's one of those claims that frankly I found hard to swallow. One can only take so many bad implementations of "virtual surround" or "MP3 enhancement" before developing a natural skepticism to such claims. But since Focusrite is an established pro-audio company with a good reputation it seemed reasonable to give them a chance. I figured at worst the thing might be competitive as a low priced USB DAC/amp, even if the VRM feature ended up being a dud.

HARDWARE
The VRM Box is a very compact unit. It measures 2.7" in length and width, and only 1" tall. That places it among the smallest devices in this segment, being just barely larger than the Nuforce uDac. The enclosure is silver plastic with a nice looking gloss-black top which ruthlessly highlights fingerprints. A small LED gives the status: LED on, for VRM being active; LED off, when VRM is disabled.

The primary connection type is USB for both power and signal. The VRM Box is limited to 24-bit/48kHz signals as played over USB, but it can accept up to 24/192 via the coaxial SPDIF input. Since there is no separate power supply, USB must remain connected even when using SPDIF. That doesn't mean a computer is always required though---I used the charging adapter from my cell phone to connect the USB cable to a wall outlet. I was able to successfully pair the VRM Box with my iPad 2 via the Camera Connection Kit. In that case the VRM Box is strictly used as a "traditional" DAC/headphone amp since the VRM software is not available for iOS.

I tried opening the enclosure to get a look at the guts but had limited success. All I could get to was the bottom of the PCB which didn't showcase anything exciting. It's always a delicate procedure when opening a review sample because you want to be respectful and not damage someone else's equipment. I'm confident that if I owned the thing I could have gone further but as it stands I reluctantly gave up. Thankfully Focusrite got me connected with someone who was able to give more specifics about the internals.

The VRM Box uses the flagship CS4398 from Cirrus Logic for D/A conversion. It also uses some form of asynchronous sample rate conversion. In this case, rather than upsampling, the device actually downconverts higher resolution signals. So a 96kHz or 192kHz track would be reduced to 48kHz, while 88.2kHz or 176.4kHz signals would convert to 44.1kHz. Bit depth remains untouched. Is there is a reduction in quality because of this conversion? Maybe. All we get to hear is the end result through the headphone jack, and there's no way to separate the DAC stage from the amplification stage in order to assess their individual characteristics. For a $99 compact device with good specifications I really can't complain.

Speaking of the specs: HERE is a link for all the details. Focusrite actually measures to arrive at these figures rather than just listing numbers from data sheets. See for example how the CS4398 DAC has a dynamic range of 120dB, and the VRM Box as a whole manages a dynamic range of 108dB (which is still very good). Measured SNR, channel isolation, and THD+N are also quite respectable.

I particularly liked the volume control. My first impression was that it had to be done in the digital domain---it was very smooth and linear with great channel balance, unlike many low budget units I've experienced. But Focusrite confirmed that it is a standard analog potentiometer being used. Bravo.

A key figure for our purposes is the output impedance of the headphone section. Unfortunately it is rated at 10 ohms which is not ideal. More on that later. The given output is 30mW at 50 ohms and 15mW at 150 ohms. Clearly this is not a powerhouse of an amp, but it ended up being adequate most of the time. I did occasionally wish for a little extra volume with certain headphones depending on the music I used.

Virtual Reference Monitor
So far I've covered the VRM Box as a compact DAC/headphone amp unit, and it does function pretty well in that capacity. But the VRM functionality is what makes the device unique. Virtual Reference Monitoring is handled through special software which gives a choice of different rooms and different speakers to simulate. Ostensibly, this is intended to be helpful when dialing in a mix, in lieu of being in a real studio with several pairs of reference monitors. It can also just be fun to listen to.

The VRM software runs separately from whatever playback software you prefer to use. It gives three choices of rooms: living room, bedroom studio, and professional studio. The room you select determines acoustics but also gives different choices in speaker emulation. There are a total of 15 options for speakers. Some are nice--Adam S2.5A, Genelec 1031A, KRK VXT8. Others are deliberately terrible--you can choose a "Computer Desktop" speaker modeled after some cheap Creative brand speakers, or even a simulated LCD flat panel speaker. The complete list is available HERE. Some of them show up with descriptions rather than the actual name--KEF Q55.2 becomes "British 90's Hi-Fi," Alesis Monitor One becomes "US Passive Nearfield," Yamaha NS-10M becomes "Japanese White Classic."

But does it actually simulate the sound of real speakers?