Benchmark DAC1 USB (2007)
A studio converter that finally let the computer into the control room - for $1,275.
Overview
The DAC1 USB showed up just as computers were turning into recording, editing and mixing machines. The original DAC1, Benchmark's under-$1,000 reference converter, had already earned a reputation among engineers for its measured performance and utility. The USB version added the obvious thing: a computer connection. Benchmark priced the made-in-USA DAC1 USB at $1,275. Pro Audio Review (July 2007, p.10) opened its review by noting that the company had introduced the original under-$1,000 reference stereo DAC a few years earlier and that the magazine had thrown accolades at it. The USB model was the follow-up, with subtle component changes aimed at improving compatibility with outboard gear.
The headline spec is a 24-bit/192-kHz converter, but how Benchmark handles sample rates is the thing to understand first. According to Pro Audio Review (July 2007, p.12), the designers chose to up- or down-sample everything to 110 kHz. They judged that the chipsets and digital filters simply don't work as well at 192 kHz as they do at 96 kHz, and that 110 kHz was the optimum point for the process. That explains the reduced high-frequency bandwidth at 192 kHz and 176 kHz - audio at those rates is downsampled, while material from 32 kHz through 96 kHz gets upsampled. It's an engineering choice, not a limitation, and the review's bench testing backed it up.
The same review measured the noise floor under several conditions. With a 44.1 kHz, 16-bit signal, the wideband signal-to-noise ratio came in at 88.0 dB, 93.8 dB across a 22 kHz bandwidth, and 95.8 dB A-weighted. At 96.0 and 192.0 kHz sample rates the wideband figure was 89.0 dB, with 22 kHz bandwidth at 113.0 dB and A-weighted at 115.5 dB. Linearity error held to under 0.001% from 20 Hz to 20 kHz, under 0.0014% across the same band at higher rates, and under 0.003% from 20 Hz to 38 kHz. The main output levels, with the switch in the calibrated position and a 0 dBFS input, measured 2.001 V on the unbalanced outputs.
Connectivity is where the DAC1 USB earns its keep in a studio. It carries AES/EBU on XLR, TOSlink optical, and coaxial S/PDIF on BNC, plus fixed and variable RCA and XLR analog outputs - the same I/O set as the non-USB DAC1. The USB input itself is USB 1.1, and that was deliberate. Pro Audio Review (July 2007, p.12) reported that Benchmark settled on the 12 Mb/s USB 1.1 conduit for two-channel 24-bit/96-kHz computer compatibility because it requires no special drivers across the various software programs people actually use. The bandwidth is more than sufficient for two channels of high-res audio, and the box works when you plug it in.
The headphone section is a major reason owners kept these on the desk rather than in the rack. The DAC1 USB uses Benchmark's HPA2 headphone circuit, and the outputs include a 10 dB gain-reduction jumper that restructures the circuit to better suit high-sensitivity headphones. One output also has a defeatable mute-on-insert function, which simplifies switching between headphone and loudspeaker monitoring. Pro Audio Review (July 2007, p.13) summed it up as getting a DAC and a major Class A headphone amp in one chassis, with one more input option.
On the technical side, the converter uses an AKM4114 AES digital audio receiver, selected for its ability to recover data under adverse conditions - high jitter, high noise, low digital signal levels. The USB input at up to 96 kHz and 24 bits is handled by a TAS1020B running Benchmark's native USB firmware. The interface clocks are isolated from the D/A conversion clock, and the AK4114 and TAS1020B are not used for conversion clock recovery. The coaxial, XLR, and optical inputs operate at sample rates up to 192 kHz.
The jitter performance is the part that gets talked about, and the bench work bears it out. Pro Audio Review (July 2007, p.13) ran a test injecting a 500 Hz sine-wave jitter signal alongside a 1 kHz, 0 dBFS tone at 44.1 kHz/24-bit. In converters that are susceptible, that test produces distortion sidebands at 500 and 1500 Hz. Through the DAC1 USB's AES input, no such sidebands appeared, and playback via the USB input produced virtually identical results. The reviewer's conclusion was blunt: USB performance is comparable to the regular digital inputs.
In use, the sound is described in terms familiar to anyone who has spent time with Benchmark converters: very accurate playback, a strong sense of space, and detail in well-recorded PCM. Pro Audio Review (July 2007, p.10) noted that drum cymbals, guitar, and other intense transients were in abundance, and that the newer USB version sounded slightly more present than the original DAC1, with a bit more openness through AKG K 701 headphones. The review also flagged the analog output line having a bit more drive for difficult preamps than the original.
There are a few quibbles. The DAC1 USB has no power switch. The reviewer raised this, and Benchmark responded that automatic power management turns off portions of the internal circuitry and the LED display when no digital input is present, and resumes when signal returns, making a switch unnecessary. There's also no incoming status display of word length and sample rate, which the reviewer noted no small high-end converter he'd evaluated had either. On the computer side, the host machine's sample-rate settings need watching. Pro Audio Review (July 2007, p.13) found that an Apple system was sending out 44.1 kHz downsampled audio until manually switched to 96 kHz, after which a 24-bit/96-kHz guitar track DVD-V sounded much better. The Apple system sample rate does not always follow the source audio. That's a setup issue, not a converter fault.
The manual is one of the better ones. Pro Audio Review (July 2007, p.13) called it as good as there is, with detailed, informative, easy-to-read information and factory bench-test measurements, plus some interesting observations on Apple versus PC implementation of digital audio.
Benchmark built the DAC1 USB alongside the standard DAC1 (AES/EBU, S/PDIF, and TOSLink inputs) and later the DAC1 Pre. The Pre added RCA analog inputs that bypass the converter to keep an all-analog path through the headphone jack and line out, and was priced at $1,595. The DAC1 USB sits in the middle: the original converter's measured performance with a driverless computer input added. Pro Audio Review (July 2007, p.13) framed it as a perfect mate for Windows machines with no built-in digital audio I/O, and noted its sound quality was better than most of the FireWire or USB interface box converters the reviewer had heard.
For anyone buying today, this is a 2007-era box with USB 1.1. That means 24-bit/96 kHz over USB with no driver hassle, but it also predates the USB 2.0 and asynchronous-USB era. The AES, coaxial, and optical inputs still handle up to 192 kHz, and the HPA2 headphone amp remains the reason many of these never leave the desk. The absence of a power switch is a genuine annoyance for anyone who likes a hard off. The DAC1 USB is a mastering-grade converter with a computer input, built in Syracuse, New York.
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