Digital Processor Reviews

What was weird was that, while setting levels, as I switched back and forth between DACs with the pink noise running, there was a slight difference in the character of the sound. After I'd adjusted the NAD's volume trim, the SPL meter read "0dB" for each DAC, but something subtler was going on—the tonal quality of the pink noise shifted just a little in the room. Later, I figured out what this meant musically.

All My Lovely Goners, the latest release from Winterpills, is a great Americana record (CD, Signature Sounds SIG 2044): folky, rocky pop that strikes me as the kind of album I wish Neil Young would get down to business and make—you know, with catchy tunes and harmonies. In this world of accolades for Fleet Foxes and Bon Iver, I wonder why Winterpills isn't getting more notice.

Anyway, listening to the first couple tracks through the NAD revealed the music's wholesome and well-appointed arrangements, which rock out in places but also sport acoustic guitars and harmonies galore. This isn't a demo-grade recording—the sound is somewhat confused and brassy when things get complicated—but via the NAD it was thoroughly enjoyable and never grated. The M51 projected a rich, lovely sound that wasn't too forgiving, which was to its credit. I like to hear a recording's technical warts, if any.

Next up was Nils Petter Molvær's Baboon Moon (CD, Thirsty Ear 57201). There's a lot going on here, with Molvær's wandering, plaintive trumpet set against a dark, churning background. Here is where the NAD's ability to handle rumbling bass and spatial character revealed a taut and capable DAC. But this album is a torture chamber of tangled bass, and I sensed a very slight thickening compared to the Benchmark. Or perhaps the Benchmark was a touch too thin . . . ?

Exploring this further, I compared the NAD to Ayre Acoustics' QB-9 DAC via both models' asynchronous USB inputs, using my Apple laptop running iTunes and Amarra. I cued up Nick Lowe's brilliant sophomore album, Labour of Lust (CD, Yep Roc YEP-2621), and cranked through the first four songs several times, occasionally tossing in the Benchmark. The NAD had all the inner detail of its venerable rivals, which many lesser DACs lack. All the musical detail was there, and it sounded as if there were more meat on the musical bones than with the Benchmark—though the NAD lacked just a nanotad of the Ayre's punch and square dynamic edges. The Benchmark sounded more like the Ayre in this regard, but overall wasn't as finessed and musically pleasing as the NAD. I would still choose the Ayre if USB were all I needed, but the NAD didn't embarrass itself; in fact, it impressed me, especially in light of its features and lower price.

I also ran my iPad as a digital streaming source, using the clever USB adapter trick that Michael Lavorgna details at www.audiostream.com. No problems running it straight into the M51's USB input and playing a CD rip—Roxy Music's For Your Pleasure (Reprise 26040)—that I'd transferred to the iPad at full resolution. Interestingly, this trick works with the Benchmark too, but not with the Ayre. I tried everything, but could never get the iPad to play through the QB-9's USB jack.

HDMI benefits and limitations
Finally, I connected the HDMI output of my Oppo BDP-83 universal Blu-ray player to the HDMI input on the back of the NAD and popped in a DVD-Audio disc. Because I'd already ripped this disc to the Sooloos as 24/96 files, this seemed a great time to compare the NAD's inputs. I cued up the Doors' L.A. Woman (DVD-A, Elektra 755975011-2) on both the Oppo and the Sooloos and, using the NAD's remote, switched back and forth in real time.

The M51's HDMI input is stereo only; comparing the Sooloos via S/PDIF to the Oppo via HDMI, I heard, right off the bat, a big difference in volume level between the two feeds. After a bit of testing and more pink noise, I found that the Oppo-NAD HDMI combination was a full 8–9dB lower in level, according to the NAD's readout. Once this was sorted out, it was a bit of a pain to go back and forth between the two sources, adjusting the NAD's volume each time, since I couldn't trim each input. But after doing just that several times, it was apparent that Oppo vs Sooloos was as close to a tie as I could hear. The NAD's display reported that the Sooloos was sending the correct 96kHz stream across, and the HDMI from the Oppo was also running at 96kHz.

I played a Neil Young DVD-A in the Oppo via HDMI, and the NAD M51 displayed the correct 176.4kHz sampling rate. I then grabbed an SACD of Mike Oldfield's Tubular Bells and popped it in the Oppo. Uh-oh. This time the M51's display read 88.2kHz—clearly, an SACD stream fed to the M51's HDMI input will be downsampled to PCM. NAD has confirmed that the M51 can't accept DSD audio via HDMI, but can accept SACD playback if converted by the BD/SACD player at up to 24/192 PCM.

Morten Lindberg, from Norway's 2L label, had recently sent a bagful of music-only recordings on Blu-ray that contained two-channel, high-resolution PCM tracks along with surround-sound versions in various configurations. I put the 2L sampler in the Oppo and once again hooked up via HDMI. The NAD's display jumped to 192kHz. Over the next few nights I played several of the 2L discs, even transferred some of the included 24/96 FLAC files to the Sooloos, and bathed in the glorious detail coming out of the speakers. Kal Rubinson and John Marks have been singing the praises of Blu-ray audio for months, but this was the first music-only BD I'd run in my system this way. I now understand what all the fuss is about.

Conclusions
I admit to having been a little suspicious at first of the PCM-to-PWM approach that NAD has taken in the M51. That was before I'd had a chance to live with it for a couple months. Nothing raised an eyebrow, and the claimed benefits in jitter rejection and filter design have obviously paid off.

I prefer DACs that reveal as much as possible about what was captured on the tape or in the digits, and couldn't care less about adding a rose-colored tint to dodgy digital sound. In this regard, the NAD M51 succeeds with a wonderfully detailed and revealing sound best described as honest, with a friendly smile. And it was a pleasure to listen to.

In other words, bitstream brilliance.