While I wouldn’t call any of 64 Audio’s hybrids neutral, I would say they all strive for a fairly balanced tonality. Yes, each IEM has its own splash (or two) of colour, but there’s no wild colouration going on that pushes any of them into a corner. There’s an undercurrent of warmth that makes listening to all four IEMs very pleasant, which is more evident in some (Nio) than others (Fourté). There’s also a natural smoothness to the sound that softens some of the harsher edges, but again this varies quite markedly. Overall, I’d say all four IEMs have been, to my ears anyway, very tastefully and deliberately tuned, even though some of the choices 64 Audio made won’t be to everyone’s taste.
Nio is tuned with a mild L-shaped signature or more of a W, depending on which Apex module you’re using. I’d call the M15 more of the latter, with its midbass-centred elevation (which is well above neutral, mind you), giving the overall tonality a warmer, darker, more organic appeal than the lighter, nimbler mX. With mX, the signature is more of a W, but a gentle one given that neither bass nor treble are dominant.
That said, in both configurations, Nio is still more natural than analytical; in fact, you can argue that Nio doesn’t lend itself to analytical listening at all. The added thickness of the bass with M15 is only really problematic with music that is already bass-thick, and any hint of veil is only there when compared to the other hybrids with their even more neutral, drier midrange. Nio’s is a safe tuning in that there are no sudden peaks or dips to make the music sound wonky or uneven, making for a very relaxed, easy listen.
With a mild-ish V-shaped tuning, Trió is all about energy and detail in equal measure. Trió displays resplendent control in every department, from a bass that’s bold but clearly delineated from the mids, to a midrange that openly flirts with neutrality while retaining a hint of warmth to keep things interesting, and a treble that cares not for restraint yet somehow mostly stays on the safe side of piercing.
That’s not to say Trió’s tuning is without issues. For example, there’s something going on with Trió’s lift in the lower treble following a sharp upper-midrange dip that adds a glassiness to the trailing edge of some female vocals, and the impressive treble energy can be a bit too zingy at times. These anomalies are rare, though, usually only showing up in brighter or poor recordings, and overall Trió’s is a mature tuning, making for an exciting, dynamic listen.
Either skewed W or bright-leaning U is how I’ve heard the Fourté’s tonality described in the various reviews I’ve read, but to my ears it’s more former than latter. While its treble elevation and energy is definitely the dominant factor, this doesn’t overpower the bass or the mids on well-recorded, well-mastered tracks. Fourté’s is not a neutral tuning by any measure, nor is it strictly ‘reference’, with some dryness in the mids and a hint of warmth and smoothness that makes it effortlessly listenable for long sessions.
Fourté’s tuning challenges convention. Its sound doesn’t come at you from predictable angles, but instead jumps out from odd angles that could take some getting used to at first, especially with familiar music. It’s not a linear tuning like Nio or Trió; rather, it keeps you guessing, filling the virtual space with sound that appears out of nowhere. Vocals can be intimate or distant, depending on the track, and sometimes both on the same recording. This unpredictability has lead to some people calling Fourté’s tuning wonky, but to me it’s delightfully quirky, making for a big, airy but ultimately highly refined listen.
Describing Noir’s tonality as a fuller, warmer Fourté does great disservice to its tuning. While it shares many of the technical traits of its twin, Noir reigns in Fourté’s occasional brashness, adding a richness from its midbass, some wetness in the mids, and dropping the temperature on its treble to create more cohesiveness and very different tonal balance.
Noir’s superpower is its ability to maintain world-class clarity despite its warmth, which – considering how closely it graphs to the Fourté – must be down to more than just tuning alone. Bass is big, and occasionally bloomy, but that bloom never suffocates the other frequencies to the point where clarity is negatively impacted. Treble is likewise elevated, but also smooth, and mids are raised enough to excite without becoming shouty.
Noir’s sound is for sure denser than Fourté’s, but it’s all muscle no flab, and ultimately presents a very engaging listen.
Heidi Talbot’s If You Stay, from her 2008 album In Love + Light, opens up with a delicate interplay between two acoustic guitars, overlaid by Heidi’s wispy vocals. Nio’s warm, inviting, organic M15 tonality makes it sound like liquid honey. With mX, the guitars have substantially less tonal weight and Heidi’s vocals are less syrupy too, but the overall tonality is still warm enough to evoke images of a fireplace on a cold winter’s day. Trió tones down the warmth quite substantially in the vocals, but the low notes on the guitar still resonate with a warmer, thicker decay, even more so than Nio. There’s more of an edge to the vocals too, belying Trió’s slightly dry voicing with upper register female vocals, and the strings have more bite to them as well. In contrast to Trió’s fuller tonality, Fourté is clearer but also smoother. Heidi’s vocals are more forward, breathier, and the strings have a lighter, airier touch to them. Noir’s inherent warmth is complemented by its exceptional clarity. Vocals are pushed a touch more forward than Fourté which, combined with a forward treble, does make them a hint splashier, but the musicality is off-the-charts good with this track.
Boston’s More than A Feeling, off their eponymous 1976 debut, is a brighter recording that greatly benefits from Nio’s warmer M15 tonality. Drums have great weight to them, and the guitars, while not quite as energetic sounding as I’ve heard them with faster IEMs, still have plenty of crunch. Nio mX lacks that extra weight and bite, and its tonality is flatter with this track. Vocals are pushed more forward, with the instruments playing a supporting role. Despite a leaner touch, mX maintains Nio’s inherently warm smoothness, but perhaps a touch too sedately in this case. Trió restores Nio’s M15 weight, bringing both drums and guitars to the fore while pushing the vocals back. It’s a fuller tonality too, but more nuanced and detailed, with just enough bite to satisfy and significantly more energy too. I wasn’t sure quite what I’d get with Fourté’s brighter tonality, and while it’s indeed brighter than Trió and Nio, it’s also smoother, more balanced and more revealing. Vocals are also more lifelike, and the guitars, drums and vocals don’t compete for space but instead are perfectly balanced in the mix. Noir maintains that balance, but injects it with its trademark warmth. Vocals are wetter, drums are fuller, guitars maintain their edge, but there’s also more contrast between the warmth and the occasionally sharp treble bump that makes trailing vocal edges and guitar riffs stand out more than they do with Fourté.
Dire Straits’ Brothers In Arms, the title track from their 1995 album (2015 20th Anniversary DSD remaster), mixes synth effects, a low, rumbling bassline and Mark Knopfler’s iconic guitar and vocals to create a delicately rhythmic and ultimately very dynamic track. Nio does a commendable job with its inherently relaxed tonality, adding just the right amount of weight with M15 and resolving the softer vocals better with mX. Trió offers up more contrast between the smooth vocals, poignant guitar and drumstick hits, its deeper low end neatly balancing out the brighter parts of the track. The rumbling thunder in the intro fills up Fourté’s massive stage, creating an enormous sense of space for the song. Stick hits echo into the distance, the vocals perfectly centred, guitars blending in with the synths and other effects, matching the ebb and flow of the track as the story unfolds. Noir’s stage isn’t quite as large, but its pacing is superb, adding a softer rumble like Nio, with fuller, warmer vocals than Fourté giving the track more intimacy.
Sarah McLachlan’s Angel, from her 1997 album Surfacing, has to be one of my all-time favourite tracks, creating a very deep emotional connection almost as soon as I hear the opening piano chords and Sarah’s otherworldly voice. Nio’s M15 tonality gently cushions each key strike, and gives the lower registers a warm, weighty resonance. Sarah’s voice comes across as ethereal, with a dream-like glow that makes me close my eyes and allow the music to quietly flow over me. The same Nio softness is still there with mX, though not quite as dream-like. With Trió, the edges of the piano keys are better defined, with excellent balance and weight, but Sarah’s voice loses some of that captivating Nio fullness, becoming drier, and is set slightly back on the stage. There’s also a bit of glassiness in her breathing that wasn’t there with Nio. Fourté’s tonality is dead-on perfect with well-recorded piano tracks, and this is no exception. Every strike is rendered with great detail, and just the right amount of sustain to sound utterly lifelike. Sarah’s voice, while not quite as dreamy as it is with Nio, sheds all of Trió’s glassiness and is also set more forward. It’s an airier, lighter voicing, but also very believable, with a subtlety that belies the emotion in her words. Noir’s thicker tonality translates into more weight in the piano strikes, but without any of the bloom or softness of Nio or the elevated heft of Trió. Sarah’s voice is fuller too, but also warmer, with a slight wetness that makes it more palpable and intimate.