Benchmark Media introduced the company’s under-$1,000 reference stereo DAC a few years ago, and we threw accolades at it. The master reference sound quality, excellent utility with plenty of I/O options and exemplary measured performance, made this DAC a favorite among discriminating engineers.
Fast forward to 2007. With more and more computers functioning as record/playback, editing and mixing machines, Benchmark has added USB connectivity to the DAC1 and made some subtle component changes to improve its compatibility with outboard gear.
Technical Insight: Benchmark DAC1 USBAccording to Benchmark Media Systems Designer John Siau, the DAC1 USB uses an AKM4114 AES digital audio receiver that was selected for its ability to accurately recover data in adverse conditions that include high-jitter, high-noise and low digital signal levels. The coaxial, XLR, and optical digital inputs operate at sample rates up to 192 kHz. The DAC1 USB inputs at sample rates up to 96 kHz and 24 bits are handled by a TAS1020B running Benchmark’s native USB firmware.
The DAC1 USB does not use the AK4114 or the TAS1020B for conversion clock recovery. The interface clocks are isolated from the D/A conversion clock.
At the core of the DAC1 USB, an AD1853 D/A converter operates at a fixed frequency derived from an ultra low-jitter crystal oscillator. This D/A circuit was selected because of its low distortion. The transition band of the digital filter in the AD1853 is frequency-shifted by upsampling to 110.633 kHz. The upsampling process eliminates alias effects caused by near-Nyquist audio content.
The upsampling is asynchronous and is accomplished with an AD1896. This device was chosen for its low spurious tones, low distortion, and exceptionally low PLL corner frequency. The PLL has a corner frequency of 2 Hz and provides 100 dB of jitter attenuation at 1 kHz.
— John GatskiThe $1,275, made-in-USA DAC1 USB is a 24-bit/192-kHz converter that operates at a 110 kHz sample frequency; Any sample rate audio played through the DAC1 is either downsampled (from 176 kHz or 192 kHz) or upsampled (from 32 kHz through 96 kHz). Like the non-USB DAC1, the USB brethren offers the outstanding HPA2 headphone circuit, AES/EBU (XLR), TOSlink and coaxial SPDIF (BNC) inputs, as well as fixed and variable controlled RCA and XLR analog outputs.
The big difference, of course, is the addition of USB input to allow flexible routing for computer audio use. According to Benchmark, the designers settled on USB 1.1 for two-channel 24-bit/96-kHz computer compatibility because it requires no special drivers to use with the various software programs. The 12 Mb/s USB 1.1 conduit has plenty of bandwidth and data transfer rate for two channels of high-res audio, and offers a connection option that is common to almost any modern computer.
Spec-wise, the Benchmark offers the same excellent, accuracy, signal-to-noise and jitter reduction performance of the original DAC1. The analog output line output has a bit more oomph for driving difficult preamps than the original. And the headphone outputs feature a 10 dB gain reduction jumper that restructures the circuit to better suit high-sensitivy headphones; one output also features a deaftable mute-on-insert function to simplify switching between headphone/loudspeaker monitoring.
I first listened to the DAC1 with a variety of sources, including the TASCAM DV-RA1000 an Alesis Masterlink and my G5 Apple desktop system via AES/EBU output. With 96 kHz and 44.1 kHz sources it sounded like the original DAC1, though I thought it sounded a bit more open when listening with the AKG K 701 headphones. The newer version sounded slightly more present than the original. Maybe my original DAC1 needs a tune-up.
I also connected the the DAC1 USB into my reference listening system with Pass X350.5, Coda preamp and the DV-RA1000 as the source. The Benchmark characteristics of very accurate playback, a great sense of space and detail of well-recorded PCM audio was obvious. Drum cymbals, guitar and other intense transients were in abundance.
After several days of listening via the AES/EBU to get an audio reference, I then connected a MacBook Pro to the DAC1 via the laptop’s USB and optical digital output in order to switch back forth between the two conduits. I heard no difference in the audio quality and no disruptions, spitting or sputtering. The USB stream worked flawlessly.
I did discover that you need to pay close attention to the internal sample rate settings of the Apple computer; you have to make sure that when you play 96 kHz audio, the Audio/MIDI system set up is set to 96 kHz. The Apple system sample rate does not always follow the source audio. I played a Toast-authored DVD Video disc with 24-bit/96-kHz stereo guitar tracks, and monitored via the DAC1.
It did not sound high-res, so having been tipped off about the Apple audio sample rate setting not matching the source, I opened the Audio/MIDI Setup menu and the system was sending out 44.1 kHz internal downsampled audio. I manually switched to 96 kHz, and the guitar track DVD-V sounded much better.
The Benchmark’s USB DAC actually creates digital output redundancy for Apple computers since the high-end Macs already allow digital input and output via optical at up to 96 kHz. Many Windows machines, however, don’t have any built in digital audio I/O. Thus, the Benchmark USB DAC1 is a perfect mate for those computers with no other digital connection. And its sound quality is better than most of Firewire or USB interface box converters that I have heard.
- Glitch-free USB 1 audio input
- Very accurate sounding PCM converter
- Audiophile-quality headphone amp
- Balanced and unbalanced outputs
- No power switch
- No bit/word status display
One of the best sounding DACs available gets a computer interfaceI have only minor quibbles with the DAC1. It still does not have a power switch (The Mytek has a nice rocker switch mounted on the front). [Benchmark responds: Automatic power management turns off portions of internal circuitry/the LED display with no digital input present, and resumes, making a power switch unnecessary.] And no small high-end converters I have evaluated have any incoming status display of word length and sample rate. On the plus side, the manual is as good as there is, with detailed, informative and easy-to-read info and factory benchtest measurements. The manual also contains some interesting Apple vs. PC computer observations relating to implementation of digital audio.
Benchmark has taken the top-performing, low-jitter DAC1 and given it a USB connection that makes it compatible with virtually any computer. For simple two-track monitoring, the DAC1 USB also eliminates the need for extra sound cards and breakout boxes — USB or Firewire. The feature adds quite a bit to the price, but you are getting a DAC and a major Class A headphone amp in one chassis — with one more input option.
Apple MacBook Pro 17-inch, Benchmark DAC1, TASCAM DVRA-1000 DVD recorder, Alesis Masterlink, Pass Labs X350.5 power amplifier, Legacy Codas preamplifier, AKG K 701 headphones.