This is easier said than done. First of all, there isn’t complete agreement about what the frequency domain effects of HRTFs are. The HRTF has to be observationally derived and with the inevitable variations between human research subjects it is easy to see why there might be divergent viewpoints on HRTF effects (interestingly, the most famous paper on HRTFs measured a mere 10 subjects, though even if hundreds were used we’d still be talking about averages). Second, getting a low-distortion driver to render the inverse of the HRTF frequency response curve is difficult. Headphone makers have to create a carefully shaped peak in the upper midrange and lower treble which is a quite different goal than what they’re tying to achieve with loudspeakers or microphones, where ruler-flat frequency response is generally the order of the day. Finally, HRTF isn’t just a frequency response concept, but also a timing concept.
Digital signal processing would seem to be called for given all this complexity, but the price and power requirements of the headphone market generally work against that approach. Say a prayer that all those “ridiculously” expensive headphones will be market successes if you really want great headphone sound in the future.
The reader may be wondering at this point why I’ve provided a mini-treatise on headphone design issues instead of covering the B&W P5 headphones. Well, it is because the P5 so simply and stunningly gets this HRTF compensation right. In the P5 we have a loudspeaker maker doing something objectively quite different from a loudspeaker and in the process showing up a bunch of headphone manufacturers who’ve been at it for decades. I was surprised, to say the least. The midrange and treble of the P5 sounds quite natural, and they make you realize (even if you’ve spilt many a word on the subject) how subtly but importantly most headphones deviate from the ideal.
To be specific, the upper range of the P5 does a few things better than most, and you need to know what these are, especially if overall accuracy and naturalness are part of your headphone quest. First, the P5 treble sounds quite fine grained. Instruments and voices have a smoothness combined with a level of detail that is aligned with the way things sound in reality. Related to this, the P5 does a fine job of producing low-level midrange and treble sounds. You need this to hear the space where the recording was made and to hear the upper