Digital Processor Reviews

I don't know whether the makers of Bricasti Design's M1 D/A converter ($7795) consciously subscribe to W. Edwards Deming's famous 14 principles of management, but they sure do seem intent on continuous improvement. The ink was hardly dry on my March 2012 Follow-Up on the M1's new filter set (which provided a greater number of intermediate steps in the range of rolloff options) when Bricasti Design cofounder Brian Zolner informed me that his company would shortly make available as a no-cost upgrade an even newer filter set adding minimum-phase implementations of the six most popular filters of the second filter set. (In his February 2012 cover review of the M1, John Atkinson had noted that, in view of the M1's software-based system architecture, there was no reason minimum-phase filters couldn't be offered in a firmware update. A coincidence, perhaps.)

Other companies that have implemented minimum-phase digital filters include AMR, Arcam, Ayre Acoustics (all current digital products), dCS, Luxman (three digital-disc players, all discontinued), and Meridian. Bricasti's new filter set retains all the options of the second set, and adds minimum-phase implementations of linear-phase filters (new) 0 (20kHz bandwidth, stopband at Nyquist frequency with low ripple and high attenuation) through 5 (18kHz passband version of the original low-delay Filter 4). The front-panel display now helpfully spells out whether the filter selected is Linear or Minimum.

Although minimum-phase filter implementations measure less impressively than linear-phase variants, the theoretical justification for minimum-phase filters is that they do not exhibit the pre-echo or pre-ringing of conventional linear-phase filters. Linear-phase filters distribute equally, before and after an impulse, the ringing the filter unavoidably causes. Minimum-phase filters exhibit no pre-ringing, only post-ringing. However, the post-ringing is in the range of twice the amplitude it would be with a linear-phase filter.

It now seems customary to say that a minimum-phase filter sounds more "natural" to many people, in that in nature, impulses exhibit only post-ringing (or echoes), and not pre-ringing. Pre-ringing is not found in nature and therefore is "unnatural." The analogy is a neat one, but I fear it might be another digital fausse idée claire. The whole process of chopping up analog waveforms after filtering out all content over 22,500Hz (for CD-quality recordings), then reconstructing the waveforms according to Nyquist's theorem, doesn't strike me as "natural" in any way at all. It's all "unnatural." Therefore, latching on to one laboratory test case (a single electrical impulse), analogizing it to a sound in nature, and concluding that that explains everything you're hearing, might be overburdening a slender reed of data, as comforting as that may be.

I am certain that if I think a speaker cable sounds wonderful, I can't really know whether it sounds good because of or despite its proprietary construction. Therefore, I'm keeping an open mind about whether minimum-phase filters' absence of pre-ringing on test impulses entirely accounts for what I hear with well-recorded string quartets. Perhaps it does. Or perhaps other factors are at work as well. My bottom lines are: the new filters are free; they are what they are; and if you don't like Minimum Phase 5, go back to Linear Phase 5—it's still there.

I listened to the newest filter set through: Wilson Audio Specialties Duette and Vivid Audio K1 speakers; preamp-and-power-amp combinations from Luxman (C-600f and MQ-88) and Parasound (Halo JC 2 and JC 1); a Denon DF-961FA CD player. a Musical Fidelity CDT-1 transport; an Apple iMac running Amarra; and Nordost Silver Shadow S/PDIF and Cardas AES/EBU interconnects and Cardas speaker cables.

The music I listened to ran from Rhino's boxed-set remastering of Gordon Lightfoot's evergreen If You Could Read My Mind (CD, Reprise/Rhino) and Shelby Lynne's Just a Little Lovin' (CD, Lost Highway 9789) through Johanette Zomer and Fred Jacobs' lute-song collection With Endless Teares (SACD/CD, Channel Classics 26609) and 2L's outstanding recording of the Engegard Quartet playing string quartets of Beethoven (No.10, Op.74, "Harp"), Bartók (No.3), and Nordheim (SACD/CD, 2L SACD 71).

The sound of Bricasti's M1 with the new minimum-phase filters was, in one word, richer. Lots richer. It was like going from a great cabernet sauvignon to a truly great ruby port.

In the last Follow-Up, I'd found that discriminating among the slightly different rolloffs of the Linear filters was akin to judging different brands of Dragonwell green tea. However, the differences between the Linear and Minimum implementations of the same rolloff (eg, Linear 1 vs Minimum 1) were immediately clear. (And much more readily apparent than engaging the Luxman DU-50's minimum-phase Fluency algorithm, which I found to be more of a Dragonwell-level difference.) The Bricasti's minimum-phase sound was richer—I don't think from having a different tonal center, but from having less grain, and more body and more coherence.

Among the Linear filters, Filter 1 was my strong favorite; I was just not as happy with any other inflection point. What came as a pleasant surprise was that, staying within the Minimum menu, I found I could appreciate and even enjoy nearly all the other filters a lot more. Hmmm. I carefully listened to Lightfoot's "If You Could Read My Mind" through all the Minimum filters. While I still didn't much care for Filter 0, and with most recordings still preferred Filter 1, when I switched to Filter 2 I no longer felt there had been a reduction in the amount of treble per se, but rather that the leading edges of treble sounds were now a little more gentle.

When I listened to the same track through Minimum 3, Lightfoot's voice got slightly chestier, the strings slightly mellower. Minimum 4 was a bit of a tipping point toward an "analog" sound, so it seemed a bit paradoxical that Minimum 5 wasn't that much warmer, but made the image of Lightfoot's voice appear larger without seeming to move it forward in the soundstage/ Curious. I found Minimum 5's effect appealing, even though, when I zipped back to Minimum 1, I found that filter's increased detail more satisfying overall. Of course, with recordings that are a little hot or too processed, Filter 1, in either implementation, was too revealing or edgy. Your conclusions may differ according to your equipment, room acoustics, and taste.

The M1's new software update also includes digital phase inversion (accessed via the Status button on the front panel) and a digital volume control (press Aux, which on new-production units will be relabeled Level). When I switched from Parasound's Halo JC 2 preamp to the Bricasti M1 as the line source for the Halo JC 1 power amplifiers, Shelby Lynne's "You Don't Have to Say You Love Me" was downright scary. The bass was deeper, tighter, and more powerful, and details were better integrated with the whole, especially in Lynne's a cappella intro with its artificial reverb.

In addition to the free software upgrade, Bricasti has announced two new, retrofittable options you'll have to pay extra for. First, an asynchronous USB 2.0 input port, available now. In addition to new circuitry, this requires replacing the Aux input's BNC jack with a USB jack; your unit will have to be sent back to the factory. Choosing the USB option on a new unit and retrofitting an old one cost the same: $595, which seems reasonable to me.

By the time you read this, Bricasti should be shipping a remote control of their own design, machined from billet aluminum (price TBA). They showed a prototype of the remote last April, at the NY Audio & AV Show at the Waldorf=Astoria. Remote-controllable functions will include selection of Input, Filter, and Level (if the volume control is enabled).

So my personal best just got better. I think that W. Edwards Deming would be pleased at the continuous improvement of the M1, and proud that the Bricasti Design M1 is made in the US. I'll send my review sample back to the factory for the USB retrofit, and then to JA for his measuring and listening.— John Marks