As indicated, the BD4.2 differs from other CIEM. First there are four independent sound bores, two for the bass, one for the midrange, one for the treble. Not surprisingly the bass tubes are longest. According to CEO Tatco Ma, tube length relates to path length which creates precise loading/tuning. What basically happens is that these individual tubes separate their drivers’ outputs to minimize interference. The second invention is the adjustable bass. I’ll say right here that it really works and without causing any distortion at all. Third and like Shure’s SE846, the Lear uses an acoustic low-pass filter which is rarely seen in an IEM. This affects the mid/high drivers but not the bass.

Finally the tube material is metal and again a function of response shaping and sound tuning. That’s some advanced tech for something as small as an in-ear monitor. Does it all add up to better performance? That would be the €64’000 question. Let’s look for the answer. The bass trim pot has a 10 o'clock to 8 o’clock range without numbers, dots or hairlines. To set both channels the same involves just a bit of care. In my auditions I arrived at the most neutral response at the 3 o’clock position right in the middle. A higher setting might suit lovers of dub step, electronica and Pop. It retains texture and harmonics without overloading. The other direction has the opposite effect but doesn’t eliminate deep bass. My personal trigger point or critical focus for headfi is timbre. If a saxophone doesn’t sound like one or you’re uncertain whether a violin is really a viola, "the rest is noise" as Alex Ross’ book puts it. It doesn't matter how wide it stages, how low its bass goes or how extended its decays die out.

Timbre. Rachel Podger is a most gifted violinist. Except for her Telemann disc, all her other Channel Classics albums were recorded exemplary. Take her Mozart & Haydn Duo Sonatas which show her and Jane Rogers brilliantly engineered for a remarkable combination. Their phrasing and tone modulations should be studied by any violin or viola aficionado. I’m one who won’t call out marvelous virtuosity when the string tone is dry.  Here the BD4.2 showed real ability to recreate an authentic timbre of Podger’s violin vibrato and Roger’s woody viola tone. Yet in the upper midrange of the violin, the sound lost some of its colour, making it hard to say whether this was a modern or Baroque instrument. Something in that frequency band was a bit thin. Time for another duo, this time in the Jazz idiom with Getz/Gilberto! It’s technically not a duet of course. But what else to call songs between two people who don’t speak the same language? The signature sound of Stan’s tenor sax, Joao’s guitar and Tommy William’s upright had their usual glamour but once again Jobim’s piano was a bit lean in the upper midband. That weakened its timbre. Yet textures had lovely three-dimensional presence.

Bass. At the central 3 o'clock setting, I found the relative bass balance the most natural and neutral. Here I went after timpani and upright bass for inspection. One key Romantic Italian composer for the instrument was Giovanni Bottesini. His Capriccio di Bravura is played by another double-bass virtuoso, Rick Stotijn. This is one of Bottesini’s best album even though many numbers here are actually arrangements. "Grande Allegro di Concerto Alla Mendelssohn" was inspired by Mendelssohn's Violin Concerto which Stotijn plays most charmingly. The BD4.2 presented his large instrument with great pitch and most obvious body with excellent extension.