Two years ago, I reviewed the Benchmark ADC1 A/D converter (PAR 12/05) and found it to be an excellent two-channel converter that could compete with even more highly priced converters. Now, the ADC1 has followed the course of its D/A brethren the DAC1 and has been upgraded to the ADC1 USB.
Priced at $1,775, the made-in-the-USA ADC1 USB is identical to the now superseded ADC1 in performance and function, save for the addition of the USB connection, which allows the converter to be connected to computers.
To refresh the memory, the ADC1 USB offers 24-bit operation at frequencies from 32 to 192 kHz. The half-rack unit contains plenty of I/O, including balanced XLR left and right analog inputs, single-wire 176 kHz and 192 kHz digital output, optical digital output (up to 192 kHz), BNC and S/PDIF output (to 192 kHz) and auxiliary BNC that parallels or delivers alternate sample rate signals up to 192 kHz. In fact, the main, auxiliary and the USB outputs can each deliver an indpendent sample rate at the same time.
As with the original ADC1, the unit includes a BNC sync clock input and a BNC clock output.
The USB output operates in the USB 1.1 standard, which, according to Pro Audio Review’s measurements and real world usage with the ADC1 USB, delivers transparently to the sources, such as a laptop computer. Benchmark says that the USB 1.1 protocol was used to avoid potential driver issues that can occur with USB 2.0 or FireWire drivers. The driverless USB 1.1 specification enjoys near-universal compatibility and and has plenty of bandwidth to meet Benchmark’s needs.
The front panel includes mode switch, meter display switch, first-stage left-gain switch, first-stage right-gain switch, left and right-gain trim pots, left and right- variable/fixed gain switches and a 41-step detented rotary gain control for each of the two channels. The first-gain switches enable either 0, +10 dB or +20 dB ranges. Gain can be set via the large variable channel knobs or the 10-turn input trimmer pots.
The left-side, nine-segment LED display indicates the selected sampling frequency. The Word length is fixed at 24 bits on the main output, but is adjustable on the auxiliary output. The nine-segment-per-channel LED meters indicate the overall level. The meter switch allows the level to be indicated in -6 dB or -1 dB steps. The peak hold function is enabled via the meter switch. The ADC1 USB’s other features include SMUX2 and SMUX4 output for two 24-bit channels at up to 192 kHz on an Alesis ADAT optical port.
You cannot review a Benchmark product without mentioning the UltraLock jitter-immune circuit, which is said to keep out the interface jitter and poor external clock performance from other sources. (Every Benchmark converter PAR has ever measured has been clean as the digital whistle.)
The ADC1 USB comes in silver or professional black with or without rack ears. It includes a single BNC-to-coaxial adaptor, an IEC power cord and an informative manual.
24 bit; up to 192 kHz sample rate; USB 1.1; BNC; optical main output; BNC parallel or separate auxiliary digital audio output; trim pot and primary knob gain controls
Benchmark Media Systems | 315-437-6300 | www.benchmarkmedia.comTo test the ADC1 USB, I made some 24-bit/96-kHz stereo recordings of a recent-issue Guild D55 acoustic guitar. First, I auditioned the ADC1 USB with it plugged straight into a MacBook Pro’s USB port and recording to Bias Peak 5.2. Then, I used the same recording setup (identical levels with the Shure KSM41s and a TRUE Systems P2analog preamp) through the original ADC1 via the optical output into the Mac’s optical input.
As I expected, the recordings sounded exactly the same; the USB neither degraded nor enhanced the audio vs. the optical output. No sputtering, clicks, pops or other anomalies.
Benchmark’s ADC1 USB can be classified as accurate, with excellent imaging and bass control. To evaluate the ADC1 USB’s subjective quality I even used several DACs, including the DAC1 USB, a Lavry DA10 (also reviewed in this issue), a Mytek 24/96 DAC, the Bel Canto upsampling DAC-2 and the upsampling DAC in the Esoteric DV-50. The results varied slightly under careful and multiple repeated listening, but all of the DACs relayed the Benchmark ADC1 recorded audio with precision.
I will say that, as much as I liked the ADC1 USB, I wish it had two features: an off/on switch on the front panel and a sample rate display like the new Lavry converters. The LEDs show sample rate for all the digital ouputs and the reference clock input, but it is not as obvious as Lavry’s separately-lit, sample rate legended LEDs.
It was not hard to offer a positive review of the Benchmark ADC1 USB. It offers the same sonic performance and flexibility of the original with the addition of the USB output. Apple users are lucky that all Intel computers already have 24-bit/96-kHz optical audio input as standard, which means they could already use the ADC1 and other optical output-based converters. PC users, however, should really like the USB option, since most Windows laptops don’t have optical input and have to be accept digital audio via data ports.