Music in the Round #56

Briefly, while TrueHD has always supported 24-bit/96kHz resolution, the great majority of Blu-ray discs carry audio of no higher resolution than 24-bit/48kHz-barely better than what's found on CDs. That these audio tracks typically sound better than CD, may be due to better attention to production efforts, the use of the 24-bit word length, and/or the advantage of having more than two channels to play with. Getting any studio or producer to change much of his hardware and software merely to placate the demands of audiophiles would be pointless, and Dolby has come up with a clever and sophisticated workaround.

Many of us have found that digital processing that includes upsampling of the audio-signal data can improve the sound, but since no actual new data are added in this process, it should be obvious that what's happening is a more accurate conversion to analog of the digital data. Recently, attention has focused on the digital filters used in the upsampling process, particularly the new "apodizing" approach derived from a 2004 AES paper by Meridian consultant Peter Craven. Products that include this approach range from Meridian processors and players and Ayre Acoustics DACs to Cambridge Audio's DACMagic and Rega Research's DAC—each of which has been highly praised in Stereophile's analyses of them, both technical and subjective. Nor is price a real issue here, as upsampling is now nearly ubiquitous; all that is required for an apodizing reconstruction filter, which eliminates all Nyquist-Frequency ringing that has occurred during the original A/D conversion, is the firmware for implementing the filter.

What Dolby has done—with the assistance of Rhonda Wilson, formerly with Meridian Audio and now a senior member of the technical staff of Dolby Labs' Products & Technology Group—is to make apodizing and upsampling a production option in TrueHD. This is ideal for two reasons. As Craven's paper and Dolby's literature suggest, the most effective place for upsampling to be done is early in the production or listening chains. In addition, when Blu-ray discs including this feature are available, the consumer need not buy any new equipment or download any new firmware to enjoy the benefits. BDs including upsampling are to be labeled "Advanced 96k Upsampling."

Of the handful of Advanced 96k Upsampling discs already released, I have one: San Francisco Symphony at 100, a recording of the orchestra's Centennial Opening Night Gala with Michael Tilson Thomas on the podium (BD, SFSMedia SFS 0057). While all of the SFSO's BDs are very well recorded, this one seems outstanding. Compared with the Dolby Digital 48kHz core audio track, there was no doubt that the new 24/96 track was more spacious, had more and sweeter treble detail, and portrayed a more natural decay of ambient sound. In all of those traits, it seemed fully competitive with the native 24/96 sound from such labels as Norway's 2L.

Significantly, in addition to outstanding performances of Copland's Billy the Kid: Suite, Mendelssohn's Violin Concerto (with Itzhak Perlman), and Britten's Young Person's Guide to the Orchestra, this BD includes the same performance of John Adams's Short Ride in a Fast Machine that was released on an outstanding disc with Adams's Harmonielehre (SACD/CD, SFSMedia 0053-2). Comparing the two releases revealed that, while both are sonically excellent, their masterings differ considerably. The BD is more overtly spacious and had a wider soundstage, a bit closer in perspective, and slightly brighter. The SACD was slightly less forward (though not recessed), with a softer treble and deeper soundstage. The bass and lower midrange were pretty much the same. One's preference will be a matter of taste, though I find the BD's expansive soundstage more consistent with the visual highlighting of individual players. Technically, both discs are beyond reproach as fine examples of the recording art.

I saw no "Advanced 96k Upsampling" label on the San Francisco Symphony at 100 disc itself, although the box's back cover does state that the audio was in "96kHz 24-bit" sound. We know this statement is not entirely true, but in practice, there is no reason for disappointment. Now, if we could only get the otherwise forward-thinking SFSMedia team to eliminate, or put on separate tracks, the numbingly puerile, PBS-style introductions to each piece, we might be able to enjoy the concert over and over without having to mash down the fast-forward button at the beginning of each and every piece.

Parasound Halo A 31 three-channel power amplifier
Lately I've been sampling several Parasound products in my multichannel systems, but the truth is that I've used a couple of their Zamps for years. These tiny "zone amplifiers" have been as accommodating as Li'l Abner's Shmoos, powering my rear surround speakers when I lashed up my first multichannel system, then my plain-ol'-stereo TV in the office, and filling in for any other power amps around the house. The Zamps are totally reliable and no-nonsense, and they sound nice.

So I'd waited a long while for Parasound to make an amp suitable for my main system. A trio of Halo JC 1 monoblocks would do the job, but there's already too much congestion behind my three front speakers, and I like to keep some room open for the products that come and go for review. The power amps in Parasound's Halo or NewClassic series didn't fit my needs, because they all have either two or five channels. Finally, here is a three-channel Parasound Halo amp with suitable connections and power: the A 31 ($3000).

The Halo A 31 is based on circuitry developed by John Curl for the highly praised Halo JC 1, which at $9000/pair is among the least expensive monoblocks in Class A of Stereophile's "Recommended Components." The A 31 is rated at 250Wpc into 8 ohms or 400Wpc into 4 ohms, all three channels driven throughout the audioband of 20Hz–20kHz. Inherent in the design are high current output (up to 60 amps per channel), and a high slew rate of >130V/µs—these specs alone suggested that the A 31 would work well in my system. (The remaining specifications are listed at Parasound's website.)

Though the Halo A 31 weighs 65 lbs, I had no trouble unpacking it unassisted—the handles on its rear panel let me manipulate it into position without danger of skinning my knuckles on the heatsinks that serve as the amp's side panels. As with other Halo models, the A 31's faceplate is simplicity itself. At the lower left, recessed in a groove running the width of the faceplate, is a single button, labeled On-Off, that switches the amp from standby to active status, the change accompanied by a blue glow around the button and a brighter red glow around the Parasound logo at the center top of the panel. The button surround glows red only briefly, when the A 31 is powered on from the AC switch on the rear and while its circuits stabilize. At the lower right of the groove is an LED labeled Hi Temp, which is supposed to glow red (as will On-Off) if any channel overheats. That never occurred while I used my review sample. At the center of the groove are three LEDs, one per channel, their blue glows indicating that each channel is operating properly.

On the rear panel are three groups of connectors/controls, one group per channel. At the bottom of each group is a pair of hefty multiway speaker connectors; at the top are a balanced-input XLR jack, an unbalanced-input RCA jack, and a toggle switch to choose between them. To the left of these, each channel has a gain control with a range of –6 to +6dB, which allows the A 31 to be matched with speakers of a wide range of sensitivities. The user's manual suggests that advancing the gain might lead to perceptible hiss from sensitive speakers. Heck, I left the gain at the midpoint, labeled Normal/THX (1V input = 28.28V output = 100W/8 ohms), and could hear no hiss at all, even with one ear smack against the tweeter shield of my B&W 800 Diamonds. This is a very quiet amp.

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