Accuphase DG-68
Stereophile|August 2021
DIGITAL VOICING EQUALIZER
JASON VICTOR SERINUS

A great concept—sound enough to serve as the foundation for an independent democratic nation. Yet what’s sound in one sphere doesn’t necessarily apply to sound in another, namely the rooms in which our systems reside. As much as we audiophiles may wish to declare our independence from room resonances, image smearing from first-order reflections, slap echo, and every other environmental and speaker-related factor that can handicap system performance, no mere declaration will make it so. Not all rooms—and not all components—are created equal.

To reference American mythology, Dorothy may have closed her eyes and clicked her ruby-red heels together three times as she declared, “There’s no place like home,” but she knew exactly what home felt like. Audiophiles who have only heard our components in compromised sonic environments have only a general idea of what their systems can sound like under optimal conditions. There is no there when you don’t know what “there” is in the first place.

Finding the way home

Enter the Accuphase DG-68 Digital Voicing Equalizer ($24,000). The fifth iteration of a unique component that debuted in 1997—a very different era in digital audio—as the DG-28, the DG-68 combines sound field correction, which Accuphase defines as “Voicing,” with soundfield creation, which the company equates with “Equalizing.” In “Voicing” mode, the company claims that the DG-68 “measures room acoustics accurately and eliminates extreme dips and peaks such as standing waves. This improves the localization of vocals and the expansion of sound stage dramatically.” The DG-68 can perform voicing automatically: A repeating sequence of preprogrammed, cascading multioctave tones generated by the unit is measured by a supplied microphone placed at the listening position. Manual voicing, in which the user creates a preferred target curve before the tone's sound, is also possible. Optional custom equalization, in turn, can be performed manually, using a supplied stylus to tailor the frequency-response bands on the unit’s large display. Accuphase says that “by performing ‘Voicing’ and ‘Equalizing’ [VC/EQ]1, it is possible to achieve the ultimate ideal sound.”

Accuphase’s awkwardly translated, 12-page online pdf 2 elaborates on the difference between “Voicing” and “Equalization”: “The Voicing function involves measuring the acoustic characteristics of the room and provides the compensation to achieve ideal reproductive conditions automatically or manually. The Equalizer allows adjusting the tonal result by boosting or attenuating the level of the signal in specific frequency bands. Any desired frequency response can be created.”

There’s a third function: “The Spectrum analyzer makes it possible to display the actual frequency components of the music being played by real-time analysis.”

The equalizer displays 80 frequency bands extending to 100kHz. Adjustments can be made while music plays, allowing instantaneous evaluation of the resulting sound. The spectrum analyzer divides the frequency spectrum into 35 bands extending up to 50kHz. The level of each band is analyzed and shown on screen, enabling users to determine where adjustments may be most effective.

After I had spent enough time with the unit to know what I wanted to ask, Arturo Manzano, head of Accuphase USA and of AXISS Audio, its US distributor, suggested I submit queries in writing to Accuphase’s design team in Japan. Unfortunately, the company was on an extended vacation and unable to respond until well after the review deadline, so we did the best we could. (Manzano proved quite knowledgeable about the product.)

During one of several phones and WhatsApp exchanges, Manzano succinctly summed up the Accuphase DG-68’s raison d’être. “Not all rooms are perfect,” he said. “Despite the fact that you have room treatment and room-tuning devices, there may be no way to resolve problems that the Digital Voicing Equalizer can address electronically. The product is equally effective in situations where room treatment is not an option.”

The DG-68’s plain-as-day main menu, which appears on its large, dimmable front panel, allows four choices: “Auto Voicing,” “Equalizer,” “Manual Voicing,” and “Analyzer.” All four choices are explained in a detailed, copiously illustrated, expertly translated 68-page product manual that’s included with the unit.

In Auto Voicing mode, the DG-68 can create two very different curves: “Smooth” and “Flat.” Once the curves are completed, given a unique name, and stored in memory, you can easily view the curves for the left channel, the right channel, and the two channels combined. You can also see uncorrected curves for left and right channels. Up to 30 curves and settings can be stored on a USB flash drive inserted into the DG-68’s USB slot on the rear panel.

“Smooth,” the Auto Voicing option Accuphase recommends, is designed to minimize frequency-response differences between left and right channels as it “brings out the characteristics of your speakers and the room.” Smooth creates “a very smooth response curve [that] helps to eliminate [standing waves] and emphasize the sound localization of the music source. The smooth voicing feature prevents excessive correction based on the speaker’s low-frequency reproduction capability, further improves measurement accuracy, and enhances the effectiveness of sound field compensation.”

“Flat,” the less enigmatic Auto Voicing option, is what you’d expect. During the course of the review, I created “Smooth” and “Flat” voicings many times over and spent many hours comparing their sound.

During our conversations, Manzano noted that not all room acoustics are fixed. Sonics change when more than one listener occupies the space. Some DG-68 owners create unique VC/EQ curves for different numbers of listeners.3 If the microphone is already set up, new curves can be created in 9 or 10 minutes.

And then there is equalization. Because many CDs are less-than-demonstration class—Manzano called some “virtually unlistenable”—some users create custom curves for their favorite imperfect recordings. The DG-68 is able to store up to 30 custom-labeled voicing and equalization curves in memory; users can recall whichever is most appropriate for a listening situation, music genre4, or recording.

During the approximately month-long review period, which included four hellish days during which I lost all connectivity, I stuck to the unit’s extremely powerful automatic voicing functions, which are the ones Manzano suggested I explore. Perhaps a follow-up review will be in order to explore the DG-68’s manual equalization options.

Behind the curtain

In a nutshell, the DG-68 consists of a high-quality analog-to-digital converter (employing four parallel AKM 32-bit AK5578EN), a high-quality DAC (utilizing eight ESS ES9028PRO channels operating in parallel), and a DSP based on an Analog Devices ADSP-21489 that enables 40bit floating-point processing up to 384kHz. Both the ADC and DAC circuits are equipped with Accuphase Noise and Distortion Cancelling circuitry, which utilizes feedback and feedforward loops to cancel distortion. A built-in signal generator creates the test tones used in assessing room acoustics. This technical complexity is masked by a simple-to-use automatic voicing function. After 24 years, in what’s its fifth iteration, this is a mature product.

The backstory

When Jim Austin emailed me to say that of several Accuphase products available for review, he preferred the DG-68, he added, “That should be an unusual and fun review.” He was 50% correct.

The DG-68 arrived during a crucial time in the evolution of my dedicated music room. Although my existing room treatment was quite fine, certain areas in the bass and treble have been calling for more attention. Two months before the DG-68 entered the system, I went the whole hog on some relatively inexpensive, broad-spectrum room treatment, whose efficacy was seemingly confirmed using the REW (Room EQ Wizard) room acoustics measurement program.

That’s when I ran head-on into the limitations of relying on measurements alone. While REW declared that my new ceiling panels (four of them) and sidewall panels (also four) had mostly leveled the room’s response from top to bottom, my ears and heart told me the treatment had suffocated my system. He who laments daily the loss of his flat abdomen was now gazing at flat measurements and longing for curves.

During the same week I was coming to terms with my unsuccessful room treatment choices, Demian Martin, cofounder of Spectral Audio, founder of Entec, and audio consultant to Crosby Audio Works, Rockport, Monster Products, and NuForce, wandered into Port Townsend with his wife Peggy. After a visit to the Olympic National Forest, Demian visited my music room, helped me interpret my REW curves, and played with the manual room equalization option in Roon. All the while, I was dying inside: This was not the sound I wanted a distinguished designer to hear. Nor was it conducive to reviewing equipment and recordings.

Taking my cue from The Wise Men of Chelm5, a delightful collection of Jewish folk tales that I laughed out loud to as a child, I sat for seven days and seven nights, pulled my beard, twirled my curls, and took advantage of post helm technology to come up with a marvelous solution. With more than a little help from my friends—you know who you are, bless you one and all—out went the “new” treatment and in came eight Stillpoints Clouds and four Stillpoints Aperture panels. All that remained of the previous treatment were two ceiling panels that did some good in some areas of the audio spectrum and some bad in others. Those panels, too, came down during the course of this review.

Each time I altered room treatments, or cabling, or power treatment, or equipment supports, or component resonance damping, I created new “Smooth” and “Flat” curves with the DG-68, turning VC/EQ on and off and listening intently. Over the same period, I also changed optical (internet) cabling and upgraded optical-to-electrical converters and SFP (small–form-factor pluggable; don’t ask) modules. In due time, I created and implemented 18 different “smooth” and “flat” VC/EQ curves.

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