The Legacy Wavelet II (Part 1)

by Bill Heck

As music lovers with nice stereo systems, many of us are subject to periodic fits of “upgradeitis” – the desire to change something, anything, to tweak our systems for that next level of sonic improvement. But looking at the many upgrade options in the audio world, especially the front end electronics, I think that we’re aiming too low.

The prices that we might pay certainly aren’t too low: anything but that, when the cost of fancy versions of the most basic products soar into tens of thousands of dollars. No, I’m dissatisfied because the rewards that these products aim for, and maybe even sometimes deliver, are so small. You don’t need to believe that amps, preamps, or DACs, much less cables and such, “all sound the same” to suspect that the differences among them are mostly subtle, regardless of the sometimes rapturous reports of certain reviewers. (Speakers are a different story; I’m talking about everything up to that point.)

Hey, I appreciate subtle improvements as much as the next music lover. But if I’m spending big bucks upgrading audio components, I don’t want subtle. I don’t want something that I can identify 80% of the time in a blind test; I want something that no one could possibly miss even once. If we spend serious money, shouldn't we get serious returns? Not on the edges, not tiny changes, but major upgrades, differences obvious to the most casual listener. We try to get excited about little gains, but maybe that's because it's been so long since we've had any big gains.

Let’s take a moment to think about why the effects of changing front end components might be subtle. The issue is that these components are mostly pretty doggone good already: electronics with vanishingly low levels of various distortions and digital signal sources that already provide fidelity beyond the limits of human hearing. Moreover, despite audio folklore, human hearing is not particularly sensitive to the kinds of differences (distortions, if you like) that remain at this stage of the audio reproduction chain.

So, if making the musical signal even cleaner is not where advances lie, how do we improve matters? How about changing the signal, not accidentally but with purpose, changing it so that the sound that arrives at your ears better reflects that sound that the performing musicians made originally? In other words, we can modify the signal to correct for, or adapt to, the listening room and to recover or enhance information otherwise lost in the recording process. Yes, that’s Digital Signal Processing (DSP).

Legacy Wavelet II

Enter the Wavelet II. (The original Wavelet has been replaced by the Wavelet II, which is the one that I have and am discussing.) This product, the result of a partnership between Legacy and Böhmer Audio, is a rare beast in the consumer stereo market, one properly characterized as a dedicated DSP product. Sure, there are DSP capabilities built into other products, such as AV receivers, mostly to provide room correction (with varying degrees of success) and to synthesize spatial effects in multi-channel systems. In the two channel world, the aim usually is room correction only, often as an “add on”’ for preamps and such. In contrast, the Wavelet II is primarily a DSP processor offering a unique approach to advanced room correction, plus features aimed at what we might call “music restoration”. The Wavelet II is one of a very few components that does not just sneak across the DSP frontier but bounds fearlessly past it.

To clarify, the Wavelet II does provide the functionality of a preamp and a DAC, not to mention a multi-way crossover. But these features come along for the ride, so to speak: the functions provided by the Wavelet II are built on an advanced processing platform to provide a complete front end, allowing optimization of the entire package while making things convenient for the user. (You can get an idea of how it hangs together from this block diagram at the Böhmer website.)

In what follows, I’ll focus on the unique features of Wavelet II. This means that, in the interest of keeping the length of this article under control, I’ll give short shrift to some aspects; please excuse those omissions.

Description

As with my earlier review of the Legacy Signatures, I won't go into the specifications that you can easily read here on the Legacy website, but a quick summary and orientation may be useful.

Wavelet II Rear Panel

The Wavelet II is both figuratively and literally a black box. I’ve not tried to open mine; you can get an idea of the contents by reading the description on the website. The details are proprietary, and of course with a unit like this, the real action is in the software.

Externally, the digital and analog inputs are more or less typical for a preamp. The output side is more interesting: each of the eight (not a typo) output channels sports balanced and unbalanced connections. Why eight output channels? The short answer is crossovers: I’ll describe their use below.

Wavelet Controls on Android Phone

As to the controls, there are physical buttons and a dial for basic functions on the front of the unit; I hardly ever use them. In addition, a small remote control for basic functions is included with the unit; I’ve never taken it out of the box. The obvious way to control the Wavelet II is with the browser-based app. My own daily driver is a repurposed old Android phone; my Microsoft Surface Pro works well, too, and the Legacy folks swear by iPads.

It was the work of a few minutes to figure out the control app. I particularly liked the clever “fine” volume control, which makes the kind of adjustments that you are likely to make a matter of a few taps. Another nice touch is that the apodizing filter, room correction, and Omnio functions (described below) are turned on or off with simple checkboxes, all of which are located on the main dashboard page – very handy for quickly assessing the results of each function.

Functions

Let’s walk through the major functions of the Wavelet II.

Digital-Analog Converter (DAC): Yes, the Wavelet II includes a DAC. (Do any digital products these days not include a DAC?) Of course, you could connect your source to your favorite DAC and connect that to one of the Wavelet’s analog inputs. But given that the Wavelet II digitizes analog inputs to do its DSP thing, why bother? By the way, you can switch on the fly between linear and apodizing filters (the latter to reduce pre-ringing) but that’s one of those subtle effect items that I’ll not spend time on here.

Preamp: The Wavelet II functions as a preamp. Not to insult the Legacy folks, but there are oodles of preamps on the market, a lot of them are very good, and in real world conditions, the differences among them are, well, subtle. (The Wavelet II does provide a neat set of “Contour” sliders that are unusual and particularly handy. You can read about them in the Wavelet II manual.) Subtle is not what I want to write about today, so again I’ll move on to what makes the Wavelet II unique.

Crossover: Although electronic crossovers are hardly new, finding one integrated into a single component with all this other functionality (preamp, DAC, DSP) is unusual, so I’ll spend a little time on it. Of course, a crossover is relevant only if you have something to cross over, either speakers that allow bi- or multi-amping, or perhaps regular speakers plus subwoofers.

For those readers unfamiliar with the concept of bi- or multi-amping, here’s a brief introduction. (You other folks can skip ahead.)

You probably know that your speakers contain crossovers that divide up the frequencies of music and send them to the appropriate drivers, e.g., bass frequencies to the woofers and high frequencies to the tweeters. In “bi-amping”, the idea is to insert an active (electronic) low-level crossover before the amplifier instead of relying on a passive one contained in the speakers. The active crossover thus directs bass frequencies to one amplifier and higher frequencies to a second amp. At the speaker, the bass amp connects to inputs (binding posts) that feed only the low frequency section of the speaker; the high amp connects to what remains of the speaker crossover to drive the midrange and up. To make this work, you need three things: (1) bi-amp capable speakers, i.e., having separate inputs for bass versus higher frequencies; (2) an active crossover in or after the preamp; and (3) a second amp.

Why mess with the complications of bi-amping? There are several theoretical reasons, including providing more total power to the system; moving the stress of higher power handling to just the bass amplifier; improving crossover accuracy and consistency; keeping large back EMF out of the amplifier handling the higher frequencies; and isolating distortion to low frequencies. (Details about the benefits of bi-amping can be found on the Web.)

So with the Wavelet II, the crossover characteristics specific to your speakers are programmed in before the unit it is shipped to you. If you are using Legacy speakers, the Legacy crew already knows how to program the unit for optimal performance in your system. If you are using other speakers – and indeed you can use the Wavelet II with non-Legacy speakers – you would need to supply information, such as crossover frequencies, so that they can program the unit properly.

For example, to work with my Legacy Signature speakers, two pairs of channels are set for bi-amping (L-R for highs and L-R for lows); another pair is set as full range L-R in case I didn’t want to bi-amp; and the final pair is reserved for subwoofers(s). Higher-end Legacy speakers, such as the Valor, would use all four pairs of channels for the different sections of the speakers, i.e., multiamping. If I later trade in my Signatures in favor of some other speakers, I can return the Wavelet II to Legacy for reprogramming as needed.

By the way, for those deep in the weeds on crossovers, note that Wavelet II digital crossover is itself quite sophisticated, supporting multiple parameters (slopes, delays, filters, etc.) per channel.

Room Correction: Certainly, there are other room correction systems (rather a misnomer, as it’s more like “room adaptation”), whether from makers of receivers or independent ones such as Dirac, but Legacy is the only vendor I know of offering the Böhmer system.

The Böhmer approach differs from most, perhaps all, other room correction systems in that it is primarily based on time rather than frequency, compensating for room effects within a 50 millisecond (ms) window. That long window – in audio processing terms, 50 ms is a long time – allows the Böhmer analysis to “look at” and deal with the results of multiple room reflections.

To cover the process in any detail would take us far afield; I’ll stick to reporting the results below, and suggest that you look at the detailed Böhmer website for more information.

Creating the correction algorithm for any given audio system and room is computationally intensive, so during setup you run a measurement process and the data thus collected is submitted via the internet to a high-powered server. Within a few minutes, the calculated correction algorithms are sent back to the Wavelet II. Although execution of the algorithms while playing music requires less processing power than their initial construction, the load is hardly trivial, which is why the Wavelet II contains a serious numerical processor (an Analog Devices chip with associated hardware support components).

Other DSP: Room correction is the most obvious form of DSP, but the Wavelet II offers another, or rather two others: “Omnio” and “Omnio+”. These are Legacy’s names for algorithms that “improve channel separation and restore the directional vector relationship to depth and position cues”. As the names imply, Omnio, which has been around for a few years, was the first iteration; “Omnio+” is a matter of months old, having been added in the recently released version 2.0 of the Wavelet II firmware.

Note that existing Wavelet II’s can be upgraded with this latest firmware; in other words, the functionality of the Wavelet II can improve after you buy it. We’re used to that with smartphones (and electric vehicles); how nice to see it in an audio product.

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So what’s the result? What does advanced DSP do for the sound? Does it improve our listening experience? Look for part 2 of this article shortly.