Below, I’ll provide observations on what I perceived as the effect of each of the filters on the PFE 232, though you should be aware that your own perceptions of the filters might differ from mine (which is precisely why Phonak offers you a choice).
Black filters: I found that Phonak’s Black filters yielded an extremely clear, revealing sound that placed emphasis on extended response at both the high and low frequency ends of the audio spectrum. On well-recorded material, I felt the Black filters enabled the PFE 232’s to achieve not only the most accurate, but also the most dramatic presentation possible.
My perception is that the PFE 232 offers more powerful and richly textured bass than the PFE 122, and that it also provide more delicate, expressive, and detailed upper mids and highs—facts that the black filters really help make clear. But with that said, let me add that the black filters can, when installed on the very revealing PFE 232s, become a double-edged sonic sword capable of making some records sound overly bright and perhaps slightly bass-heavy.
Gray filters: According to both Phonak’s description and to my ears, the optional Gray filters provide a broad and relatively restrained touch of midrange and upper midrange emphasis. When used on the PFE 122, I found this filter could sound a little too “midrange forward” for its own good, but with the PFE 232, which offers somewhat stronger bass and highs than the 122 can deliver, the gray filters give a more natural-sounding and pleasing result.
I found the gray filters seemed somewhat more forgiving than the black filter on less than ideal recordings, partly because they create the illusion of the PFE 232’s highs being rolled back just a touch (at least relative to midrange frequencies), which helps tame any overly sharp edges or excess brightness that might be present in the material being played, which can be beneficial.
The tradeoff, though, is that the gray filters can—at least to my ears—make the frequency response of the PFE 232 sound less fully extended than it actually is, especially in the treble region where the top-end can sound dulled just a bit. While I do think the gray has real merits, I preferred the sound of the PFE 232 with the black filters installed on the whole, though that preference is not as strong or clear-cut as it was when I used the gray filters with the PFE 122.
Green filters: Phonak’s Green filters are billed as offering “stronger bass,” but what I really think happens is that they leave bass pretty much untouched, while rolling off the PFE 232’s upper mids and highs. This response characteristic could conceivably be helpful in cases where listeners want a darker tonal balance (perhaps to help compensate for low-frequency background noises or to offset problems with excessive brightness). There is, too, the fact that some listeners just plain enjoy a sound that is, to be blunt, somewhat “bass-enriched.” Nevertheless, my thought is that most accuracy-minded listeners will find either Phonak’s black or gray filters to be a better all-around choice.
The “Core Sound” of the PFE 232: As I mentioned above, the core sound of the PFE 232 is similar to that of the PFE 122, though both deep bass and treble response are a bit stronger. But the bigger differences between the two earphones involve overall resolution and refinement—areas where the PFE 232 enjoys a clear-cut edge over its less expensive sibling. Like the PFE 122, the PFE 232 offers an open and transparent sound that is well focused and finely resolved, and like the PFE 122, the PFE 232 offers excellent transient speed and delicacy. But what sets the PFE 232 apart—especially on really great recordings—is its ability to dig much deeper into the inner details of music, and to capture considerably finer shadings of sonic nuance and expression.
The difference I am trying to describe is a bit like what happens if you listen to studio recordings through a good set of control room speakers, but then shift to using truly great speakers—so that you suddenly feel almost as if your ears and brain have been directly hard-wired to the studio console. It isn’t a matter of the PFE 122s being somehow “not good enough,” because they are exceptionally good for their price. It’s just that on great material the PFE 232 can do even more, so that listeners are able to connect in a direct and immediate way with recordings, with nothing (or almost nothing) to stand between them and their music. Personally, I find this kind of “direct connection” is worth a lot, though I think the PFE 232’s deep resolution and refinement might register mores strongly with some listeners than others.