Well, maybe not completely wrong, but maybe partly wrong. In previous blogs I delineated the electro-acoustic properties that all hearing aids should have in order to be optimized for listening to, and playing music.
As a review, an optimal hearing aid should have: a sufficiently high peak input limiting level so as not to distort the more intense stimuli associated with music; a WDRC circuit that is not that different from that for speech, a similar bandwidth than for speech, an OSPL90 setting that is 6 dB lower for music than for speech, and an omni-directional microphone. These have all been reviewed in previous blogs.
Well, where did I go wrong? Maybe hearing aid microphones don’t have to have an omni-directional response? This is one of the features that everyone just “assumed” was the case. After all, listeners will be listening to a signal that is in many cases 40-50 dB more intense than the background noise so signal-to-noise ratio issues are not an issue. And players just need to hear their own instrument and everything in comparison wouldn’t be as loud.
But, this is where I went wrong… how many times have I said that I am wrong?
It turns out that depending on the playing environment, the implementation of a directional response that would serve to minimize annoying horns and other intense instruments in the vicinity, may be a good idea after all. In this past month alone I have had almost ten cases of hard of hearing musicians (yes, I see a lot of hard of hearing musicians) where I needed to alter the directional pattern of their previously fit hearing aids.
A slight suppression of potentially masking music/noise may be a good thing after all, although it does depend on many factors such as the musician, hearing loss, and musical environment. In many musical venues there is such amazing acoustical treatment such that reverberation is minimized and a directional microphone can be truly directional.
In a typical reverberant sound field a directional microphone is rarely directional. The difference between an omni-directional microphone and a directional one is minimal at best. But a musical venue is a different story where directional may indeed mean directional.
So, go ahead and ensure that the peak input limiting level is sufficiently high (a rarity with modern hearing aids), ensure that the OSPL90 is about 6 dB lower than for speech, but maybe consider implementing a directional pattern with music.
