General Asylum: REVIEW: Accuphase DG-28 Accessory by David Spear

Background, Intro, B.S., Whatever

Buying a digital equalizer at this time was one of the tougher decisions I have had to face in putting together my system. The digital landscape is changing rapidly, new high-resolution formats are emerging, and there is a not insignificant risk that today's crop of digital equalizers will suffer from premature obsolescence and fail to hold their resale value. Nevertheless, it seems to me that digital equalization is the most effective approach in dealing with listening room anomalies that cannot be corrected by the traditional methods of careful speaker positioning and judicious acoustic treatment.

The Problem

My dedicated listening room, though rather small (I live in Japan), was designed and built specifically for audio, I have hung acoustic fiberglass panels in various strategic locations, and it took many, many months of trial-and-error experimentation to find the best positions for my speakers, subwoofer, and listening chair (i.e., the positions that resulted in the most acceptable compromise between tonal balance, imaging, and soundstage width/depth). Despite all these efforts, I still had annoying dips at 80 Hz and 160 Hz that just wouldn't go away and also occasionally noticed strange room pressurization effects in the low bass at high volume levels. In addition, the speaker positions that gave the smoothest spectral balance were nowhere near those that gave the best imaging/soundstaging, and optimizing both factors simultaneously seemed to be pretty much a hopeless task.

The Contenders and the Winner (for me, at least)

Given the above, digital equalization appeared to be the only solution. The main contenders, to my mind, were the Accuphase DG-28, the TacT RCS 2.0, the Behringer Ultracurve Pro DSP 8024, and maybe one of the SigTech units. Each of these devices has its pros and cons, and also falls into one of two competing ideological camps (i.e., impulse-based time/frequency correction [TacT and SigTech] and steady-state frequency compensation [Accuphase and Behringer]).

I ultimately decided that the Accuphase DG-28 would fit best into my system. To me, the most attractive features of the DG-28 were 1) current support of SACD (with the Accuphase DP-100 SACD transport, at least) and future compatibility with DVD-A by installing *relatively* inexpensive option boards, 2) assured compatibility with my CD player (Accuphase DP-75V), with connection/operation entirely in the digital domain, 3) no need for connection to an external computer, 4) precise 6th-octave equalization, with an automated room compensation routine and full RTA capabilities, 5) reasonable price (here in Japan), and 6) a good match with the rest of my gear, in both cosmetic and functional terms.

Description of the Unit and Connection Procedures

Basically, the DG-28 is a 64-band stereo digital equalizer with bands ranging from 16 Hz to 22.4 kHz in 6th-octave steps. It is a stand-alone unit that matches other Accuphase gear in dimensions and design (quite attractive, IMO). Included in the box are the unit itself, a small remote control, a pair of good-quality 75-ohm coax digital interconnects, a microphone, a microphone holder, and a microphone cable fitted with XLR connectors (essentially, everything you need except for the microphone stand).

Connection to the DP-75V CD player requires the installation of a digital I/O option board in the "EXT DSP" slot of the 75V. This permits the DG-28 to be switched in and out of the circuit using the "EXT DSP" button on the CD player's front panel or with the remote. Additional digital sources (e.g., MiniDisc recorders, DAT recorders, separate CD transports, Accuphase's SACD transport) can be connected to the DG-28 or the DP-75V either directly or via option boards, and other option boards are available for phono input and for connection with line-level analog devices (input/output, balanced or unbalanced). In my case, I connected my MD recorder directly to the DP-75V, permitting source switching (with or without equalization) using the 75V's remote. Connection of the MD recorder to the DG-28 is also possible, but the DG-28 does not permit the input to be selected with the remote. (More bitching about this later!)

Appearance and Layout

The front panel is quite attractive and uncluttered. The finish is traditional Accuphase champagne gold. From left to right are the power switch, the LCD panel (measuring about 3 x 4 inches), five memory buttons (A-D and "Memory", which also serve as "soft keys" depending on the panel display), a "Channel" switch (for switching L, R, L+R), an "Equalizer" switch (for bypass), a diamond-shaped array of frequency up/down and level up/down buttons, and finally a screw-mounted cover under which are located less frequently used controls (along with the "Input Selector" button, dammit!) and the microphone jack. The rear panel has paired digital I/O connectors (RCA and Toslink), an IEC power cord socket, and slots for four option boards (all fitted with screw-mounted covers).

The buttons on the small remote replicate most of the front panel switches. The glaring exception is the "Input Selector" button. Source switching can only be performed at the front panel, and to make things even worse, the "Input Selector" button is located behind the screw-mounted protective cover. This means that if you connect multiple sources to the DG-28, you will spend a lot of time removing and replacing this cover, or you will end up leaving it off all the time (and eventually losing the damn thing). Fortunately, additional digital sources can be connected directly to Accuphase CD players, permitting them to be switched using the CD player's remote. Owners of other CD players may not have this option.

Operation

Operating the DG-28 is quite straightforward and intuitive. You simply connect the microphone and place it at the listening position, set the level for each channel between a pair of reference marks on a scale, select a target equalization curve (any of four preset curves [flat, -1 dB/octave above 2 kHz, -2 dB/octave, or -3 dB/octave] or a user-created curve of any desired shape), and then press a button to start the automated equalization routine, which performs three frequency sweeps for each channel and gradually adjusts the equalizer settings to match the target curve. This takes about 5 minutes. Additional sweeps can be performed as many times as desired for greater precision. The resulting equalization curves (separate curves for the L and R channels) can be stored in any of the four user memories (A-D). In addition, manual fine tuning of measured or stored curves is possible using the frequency and level buttons, and these tweaked curves can then be stored in any memory location. Of course, non-volatile memory is used so the setting are retained even when the DG-28 is unplugged from the wall.

The Sound

As an initial test, I compared the sound of a CD (Frank Zappa's "Hot Rats", if it matters) played back on the DP-75V with the equalizer bypassed and with the equalizer in the circuit, but with all of the frequency bands set to zero. There was no difference that I could detect. No harshness, no distortion, no loss of dynamics, no compression of the soundstage, no nothing. I then ran the automated equalization routine to obtain my first set of correction curves, made some minor adjustments (i.e., pulled down a couple of narrow spikes and also the three top bands [18, 20, and 22.5 kHz] a bit), and stored the results in memory A.

Even using this preliminary set of curves, it was obvious that the sound of my system was dramatically improved. The bass response was much smoother and more extended and the 80-Hz dip that had been bothering me was completely eliminated. Much to my surprise, imaging was also more precise and the soundstage became wider, deeper, and more stable. In addition, I found that I could listen to music at higher levels (as indicated by the output level meters on my amp) without that uncomfortable "this is getting a bit too loud" feeling. Dynamics seemed to be reduced somewhat, but I feel that this is due to the elimination of the dips and peaks in the unequalized room response, which could lead to an artificial sense of dynamic contrast. All in all, I strongly preferred the sound with the DG-28 in my system.

Summary

The addition of the DG-28 has improved the spectral balance of my system from top to bottom, has noticeably improved imaging and soundstaging, has completely eliminated a couple of annoying room anomalies, and permits me to listen to music at higher volume without fatigue or discomfort -- all without introducing any noise, grundge, or digital nasties. Operation is simple and straightforward, and the unit makes it easy to achieve the desired response curve without any problems or complications. The remote is quite handy, except for the lack of source switching.

I plan to generate equalization curves for four target responses -- the unmodified -2 dB/octave target curve (which was the best sounding to my ear); the same target curve, but with the entire response tilted up/down by 1 dB at the top and down/up by 1 dB at the bottom (to replicate the "spectral tilt" control that I found so handy for program correction on the Luxman C-1000 preamp that I owned many years ago, and which I believe was also provided on the old Quad preamps), and the same target curve, but with a touch of bass boost (for "party time").

Although I am extremely happy with the DG-28, it does suffer from a number of drawbacks, limitations, and minor design glitches. Unlike the TacT and SigTech systems, it cannot correct phase/temporal problems in the room response. The unit appears to be designed specifically for use with Accuphase digital products, and owners of other brands of digital gear may find some of its features and expansion capabilities (particularly those related to SACD playback) less than useful. The silly placement of the "Input Selector" button and the inability to perform source switching with the remote are major design boo-boos, IMO. It would also be nice to have more user memories, which would make it possible to store a larger number of equalization curves. This would make the unit much more useful for program equalization, rather than room correction. Finally, the overall output level of the equalizer is reduced as the amount of boost/cut is increased, which interferes with A-B comparisons and may lead to the "accidental blast yourself" phenomenon if you bypass the equalizer while music is playing.

The only other drawbacks that I can think of are those that are shared by all such devices. The use of an equalizer requires that you have sufficient amp headroom and speaker power handling to avoid overload or damage. Most importantly, there is a grave risk of exacerbating any "audiophilia nervosa" that you may already have, since the tweaking potential is limitless -- you know, "Just moved the end table 3 inches to the left; better run a new equalization curve!", "It's a bit cooler today; run a new curve!", "The ashtray is full; new curve!", ad nauseam. (Actually, maybe the fact that the DG-28 has only four memories is something an advantage in this regard. If it had 100 memories [like the Behringer], I'm sure I'd program all of them with slightly different curves and then label all of my CDs with codes indicating which curve sounds best for each disc [or even each track!].)

Nice touches:
* Everything is provided (microphone, cord, digital cables, remote)
* When switching between equalization curves, the unit gracefully fades out, recalculates the new parameters, and then fades back in.
* Even when the unit overloads due to an excessively high output level setting (the "Peak" indicator flashes), no audible nasties are generated.
* The display can be turned off if it is too distracting.
* All settings (including display off) are retained even when the unit is unplugged from the wall.

Quibbles:
* Did I mention the "Input Selector" switch?
* Only four user memories.
* The user-set target curve starts flat. You can't edit the other preset curves. This makes generating your own curves a rather time-consuming process.

Well, all in all, I recommend the Accuphase DG-28 very highly. It has truly brought my system up to the next level.

Good listening -- Dave

PS. Special thanks to fellow inmate Kazu Kawasaki for kindly recommending the DG-28 to me several months ago.

REVIEW: Accuphase DG-28 Accessory Review by David Spear at Audio Asylum