When we reviewed the Phonak PFE 012, we found the interchangeable filters wonderfully useful. Both the mid-centric and bass/treble booster tips were perfectly valid choices, and a good way for those new to high-end headphones to find out the kind of sound signature they gravitate towards - auditioning IEMs is not something you can usually do in HMV.
The very same filters are used with the PFE 232. They come bearing a set of grey filters, which are the most balanced (Phonak says they promote mids), while a neat little toolbox houses the bass-boosting green filters, the bass-and-treble-boosting black ones and an additional set of greys. You plug them in and remove them using a little supplied tool - there's a thread on the inside of each filter to help out.
We're surprised at how badly Phonak has relayed what these filters are for, though. The manual tells you how to remove them, and they earn a bullet point on the packaging, but there's no bigging-up of Jeckyl, Hyde and Clive's skills - no detailed expounding on their sonic effects. It's a good job we've spent many hours with each, then.
Unfortunately, the filter customisation doesn't work as well here as it did in the PFE 012. After all, one wrong brush stroke might destroy a masterpiece and these dual-driver headphones are a lot higher-end than their PFE brothers. In our opinion, there are wrong and right filters to use with the PFE 232. Jeckyl and Hyde should be consigned to the past. Clive is the man of the future. Clive is the "neutral" grey filter.
Why are the other two duds? The bass-boosting green filter is effectively the difference between the PFE 112 and the PFE 012 - used to up the bass for a "lower-end" audience (no offence, like, we love the PFE 022), as both sets use exactly the same driver. They add some warmth to the PFE 232, but it's at the expense of what these earphones are really about - detail and refinement. Deliberately downgrading the sound quality of a £400 earphone seems a little bonkers to us.
Then there's the black filter, which emphasises both bass and treble. Used with the PFE 112, this is the "fun" filter, but here it over-does the top-end, resulting in a slightly harsh sound in tracks that haven't been immaculately mastered - exacerbated by the slightly scooped signature, which encourages you to up the volume a tad. Stick with the grey filter, though, and you'll be greeted by a sound more refined and insightful than just about any universal IEM on the planet.