Music in the Round #34 Page 2

Parasound Halo P 7 preamplifier
When I first heard of Parasound's Halo P 7 preamplifier, at the 2005 Consumer Electronics Show, I was excited: a high-end stereo preamplifier made by a respected company and designed to interface with a multichannel system. In addition, it looked great and was expected to have a list price of $2000. Now, almost three years later, the P 7 is finally available, and it delivers on every point.

Parasound's literature talks about the P 7 as if it is a multichannel preamplifier. It is, of course, but I think of it differently. First, it's purely analog; its multichannel performance is dependent on digital sources, whether disc-based or downloaded—the P 7 won't accept or process digital sources. The P 7 is, to me, a full-featured analog stereo preamp with six stereo inputs (one balanced), balanced and unbalanced outputs, tape-loop connections, defeatable bass and treble controls, and a really good moving-magnet/moving-coil phono stage. What makes it relevant for inclusion in this column is that it also has two 7.1-channel unbalanced inputs (which can be set up for home-theater bypass), optional bass management for all sources, and RS-232/12V connections to integrate with modern A/V systems.

The matte-finished front panel is pure Halo, its two oval buttons haloed in soft blue light. The one on the left controls on/off, the one on the right the function of the P 7's only knob. Above the left button are a headphone jack and an MP3-player input jack, and above the right a multifunction control knob. The latter defaults to a volume control, but the button below it can make it perform many other functions. In the center is a clear, multiline character display in blue.

The rear panel bristles with connectors. Across the top are the balanced inputs (2-channel) and balanced outputs (7.1-channel). Below them are RCA connectors for (from left to right): phono input, six line-level inputs, tape loop in/out, 7.1-channel output, and two sets of 7.1-channel inputs. At the right end are the power and control connections.

Setting up the P 7 as a straight-through stereo preamp was a piece of cake—and, for me, a wonderful reminder of just how easy such setups are. Connect your sources to the appropriate inputs and your amp to the appropriate outputs, using the front L/R jacks of the 7.1 set, turn it on, and you're good to go.

The accompanying remote control is capable and simple to use. The P 7 was dead silent and devoid of any switching noises via either RCA or XLR connection, and the music emerged with clarity and dynamics. In fact, I think it did a better job of driving my 10m interconnects than did my Meridian Reference 861 pre-pro. The Halo's phono stage was very satisfying, and worked beautifully with both my Ortofon SME30H and my Koetsu Black cartridges (oldsters, I know, but they both sound nice in different ways).

It's not my place here to talk about two-channel sound, so I'll add only that the P 7 can also apply bass and treble adjustments, as well as do simple but effective bass management. The latter permits crossovers at 50 or 80Hz independently for the main speakers and subwoofer, with options to roll off the L/R speakers or leave them running full-range. The Halo's bass management applies to all analog sources, except for those set for home-theater bypass (which Parasound calls Theater Bypass).

The Halo P 7 is unique in also sporting two 7.1-channel inputs, which it can handle as volume-controllable sources, or which can be set for Theater Bypass with fixed unity gain. The former arrangement means that the P 7 is perfect for expanding a high-end stereo system into multichannel audio with the addition of an SACD and/or DVD-Audio player with analog outputs. All bass management, speaker level, and distance settings would be done in the player's setup menus; the P 7 would handle input selection and volume. I was pleasantly surprised that, for these sources, the P 7 could also trim the Left/Right and Front/Rear balances. If your multichannel source is a pre-pro or AVR, Theater Bypass will bypass all of the P 7's control options, including level trims and bass management.

I connected both an Oppo DV-980H universal player and a Sony SCD-XA9000ES SACD player to the Halo P 7's multichannel inputs, and was greeted with a delightfully open, balanced sound. The P 7 ruthlessly revealed the differences between the two, particularly in contrasting the Oppo's slightly etched treble with the more smoothly detailed sound of the Sony. In this role, the Halo P 7 was a delight to use and to listen to, and clearly an advance in every way on the old Sony XA-P9000ES that introduced the multichannel analog preamp category. The Parasound's overall sound quality approaches what I hear from the Meridian Reference 861 via the latter's very competent A/D/A conversions, and from the outstanding Audio Research MP-1 I wrote about in September 2007.

I evaluated the Theater Bypass mode by inserting the Halo P 7 between the Meridian's output and my power amps. XLR-to-RCA adapters were necessary (thanks, Kubala-Sosna) because the Meridian has only balanced outputs, and Theater Bypass functions only with the P 7's 7.1-channel RCA inputs. I used the P 7's balanced outputs to drive the amps. In this mode, the P 7 was outstandingly transparent, which I proved by varying which channels were fed directly to the amps and which were rerouted via the P 7. It didn't matter—the volume and tonal balance didn't vary, nor were there any shifts of voices or instruments in the soundstage. Note, also, that the P 7's Theater Bypass inputs are unique in being able to accommodate eight channels; most analog stereo preamps with HT bypass are limited to only two. You can use, as I did, any number of those eight channels, depending on your needs and preferences.

To say that I'm enthusiastic about the Parasound Halo P 7 is an understatement. It's a superb analog stereo preamp at a realistic price, and its value increases when you realize that it's also an excellent two-input, 7.1-channel analog preamplifier with optional Theater Bypass for these inputs. It's icing on the cake that it has sophisticated control functions, renamable inputs for its display, a superb remote control, and the valuable ability to manage the bass via its stereo inputs. The Halo P 7 is the "category killer" of analog multichannel preamps or HT bypass. Nothing else I've seen can do what it does, and the few that sound marginally better cost many times more. Boy, do I wish I'd had it three years ago!

DSPeaker Anti-Mode 8033 equalizer
I keep finding new and interesting products in the field of equalization, where one size definitely does not fit all. Unless you have that rare perfect room, compensation for the effect of room modes on bass response is necessary—but different systems require different solutions. Modern A/V receivers and many preamplifier-processors have such equalizers built-in—but what about an analog system based on, say, the Halo P 7 and a universal player? They, too, are subject to the influence of room acoustics. Because bass management can be accomplished in the P 7, the easiest solution would be a dedicated EQ for the subwoofer. Conceptually, the ideal such solution was the ACEI Subwoofer Optimizing System (SOS), which I reviewed in January 2005. You simply inserted it at the sub's input, placed the supplied microphone at the listening position, pushed a button, and you were done. Unfortunately, ACEI appears to be out of business, and anyway, the SOS was an analog single-band EQ of very limited effectiveness.

The Anti-Mode 8033 from Finnish firm DSPeaker is an SOS for the 21st century. It's a plug-and-play, DSP-based, single-channel bass equalizer with up to 24 IIR (Infinite Impulse Response) filters to equalize in-room bass response. No external gadgets or PC are required. The manufacturer's website offers useful theoretical and application help here, and the price is 225 euros, which, at the time I type this, comes to $305 (add $62 for lightning-fast shipping).

The Anti-Mode 8033's tiny chassis (5" W by 1.1" H by 3.2" D) is powered by a 9V wall wart and has an RCA input jack and two RCA outputs, one in phase, the other inverted. The front panel has a microphone jack (a mike and a 20' cable are provided), a power switch, two pushbuttons, and four LEDs. The two buttons, pressed together or separately, with brief or sustained pressure, control all functions: initiate calibration, add data from an additional mike position, Lift 25 (a boost in the 15–25Hz range with a maximum of 7dB at 20Hz), Lift 35 (a boost in the 25–35Hz range that tops out at 7dB at 30Hz), and Bypass correction. Got it?

After connecting the sub output from your AVR or pre-pro to the Anti-Mode 8033's input and connecting its output to the subwoofer, make sure you power the 8033 with the sub off—there's a power transient that is surprisingly loud. Then plug in and position the mike at your listening spot, push and hold both buttons, and stand back.

After a brief delay, the Anti-Mode 8033 feeds the subwoofer a series of four automatically adjusted low-frequency sweeps. No permanent harm was inflicted on my subs, but these signals are among the most potent my system has withstood. The signal, which sweeps from 16 to 144Hz, seems capable of overloading less robust subs. Perhaps it might have been better to start the sweep at the highest frequency, or with a 100Hz test for the level adjustment. Nonetheless, I endured the four sweeps, and that was it. The Anti-Mode 8033 was on the job.

The Anti-Mode 8033 can incorporate measurements from an additional mike position. This is advisable; certainty about the strength and frequency of the room modes increases with additional samples. DSPeaker recommends two strategies. The first, Compensation of the Weakest Point, involves finding a spot where the low-frequency sound is most compromised by room modes, and using that to supplement what is measured at the listening position. Nice idea, but the user is given no tools with which to find such a spot, as one has with the Velodyne SMS-1 and its neat spectral display. The second strategy, Gradient Compensation, is to take the second measurement closer to the room corner nearest the listening position. This is likely to reveal an increased influence of the axial room modes, and is the most practical approach for most users.

The lack of any display system means that the only feedback that the average user gets from the Anti-Mode 8033 is what he hears. In that regard, the results were quite effective. Organist Cameron Carpenter's Revolutionary (SACD, Telarc SACD-60711; see sidebar, "Recordings in the Round") could not have arrived at a better time. As I randomly switched from Bypass to On, it became clear that the 8033 had cleaned up and tightened the low end. I was surprised that, in Bypass, the bass didn't seem louder, just poorly defined and of vague tonality. When I restored the 8033's EQ, each pedal tone became distinguishable. There was a similar salutary effect with low percussion and winds, and, of course, with film sound effects.

Measurements taken with the XTZ Room Analyzer confirmed that the Anti-Mode 8033 indeed smoothed the subwoofer's frequency response, but also revealed some interesting issues. Fig.1 shows how the 8033 with Gradient Compensation smoothed the response below the crossover point of 40Hz. Because the 8033 was in only the subwoofer's signal path, it couldn't correct for modes excited by the main speakers at or above that frequency. This is seen in fig.1 as a bump at 40–44Hz. Fig.2 shows that Audyssey Sound Equalizer, which also EQs the main channels, greatly reduces the bump compared with the 8033, shown in this case without Gradient Compensation. (The curves are displaced because the 8033 has higher gain than does the Audyssey.) Raising the bass-management crossover to 50Hz let the 8033 flatten the bump, and resulted in a response similar to the Audyssey's. This illustrates a limitation of subwoofer-only EQ with a low crossover, and indicates the complexity of multi-speaker room interactions. Nonetheless, the overall effect of the Anti-Mode 8033 was an audible and measurable improvement.

Fig.1, System in-room response with (cyan) and without (green) 8033 Gradient Compensation. (16–315Hz horizontal scale, 5dB/large vertical div.)

Fig.2, System in-room response with 8033 Gradient Compensation (cyan) and with Audyssey equalization (green). (16–315Hz horizontal scale, 5dB/large vertical div.)

These two graphs might lead one to conclude that Gradient Compensation was not useful, and that it actually resulted in a "peakier" response. However, Gradient Compensation did correct the main room modes better than did a single point of measurement, though this was seen only in time-domain displays (not shown, footnote 2). While the single-point 8033 EQ did reduce overall long decay, there remained significant energy at 44 and 31Hz that extended to 200 milliseconds at levels approaching 90dB. Gradient Compensation reduced those modes substantially, leaving no high-level energy beyond 90ms. It sounded better, too.

In summary, the DSPeaker Anti-Mode 8033 is a dandy little device for taking care of the major influences of room modes. It is incredibly easy to use and reasonably priced. It offers no display option and little leeway for tweaking, except for the two Lift options (which I found unnecessary in my setup). Those willing to invest more effort and money may find more flexible and more interactive options, but if you just want this important job done quickly, the Anti-Mode 8033 will do it, even with one hand tied behind your back.

Next Time in the Round
I did the rounds at CEDIA Expo 2008 in September 2008 and primed the pump for many new products. At this point, however, it's uncertain how many of the new pre-pros, amps, and players will make the transition from their makers' promises to my premises. What I can be certain about is the new and exciting v3 of the AudysseyPro software, which seems to have fulfilled my pipe dreams for new features.

Footnote 1: All processors have finite DSP capabilities, and the Integra DTC-9.8 cannot use Audyssey EQ with HD sources over 96kHz. I listened to the 192kHz tracks with the Integra using the external Audyssey Sound Equalizer.

Footnote 2: The time-decay waterfall plots are not shown because the Anti-Mode 8033 introduces a time delay of 3.8ms into the subwoofer channel. Thus, the waterfall plots for the Anti-Mode 8033 EQ and Audyssey (which also introduces its own delay) are shifted on the x axis and are not directly comparable. To compensate for the 3.8ms delay, add about 3' to the subwoofer's distance in your set-up menu.