Hearing care professionals are human beings. And we filter information like hearing solutions filter sound. We filter what we like from what we do not like, what we believe (or understand) from what we distrust, what we remember from what we prefer to forget. It is always nice to be surrounded by comfortable information that confirms our beliefs. Maybe I should have written ‘I’ instead of ‘we’ in these statements, but I was raised to avoid the ‘I’-word more than any other letter in the alphabet.
Compression may be one of those topics. We compress and believe that amplifying soft sounds more than loud sounds and mapping the world of sound into the residual dynamic range of the patient is good. And good for all patients.
We may ‘forget’ that we read or heard something about compression which was not so good, and we convince ourselves that compression always works fine. And we believe that for speech, a signal which is rapidly changing in level, the compression always needs to be fast (quick).
Compression, however, creates some distortion. That is not the fault of the technology of hearing aids – simple physics and mathematics of signal processing prove that distortion is unavoidable. So the landing of different sound levels within the dynamic range comes at a price. For some patients the price is too high. They are better off with (or they just outright prefer) less or no compression, sacrificing audibility of soft sounds. Especially in the group of severe (61 to 80) and profound (81 and above four frequency average hearing loss in dB in the better ear) there are many who do not like fast compression.
Linear amplification may be a viable alternative for them, as long as we do not activate the limiting system in the hearing aid too often. A third way is slow compression. Slow compression, with time constants in the order of seconds, preserves the speech envelope much better than fast compression. With slow compression you get closer to the original speech signal. Research has shown that this leads to improved vowel recognition for some patients.¹‘²
I (we? :)) imagine you can think of numerous patients with significant hearing losses who’ve been difficult to fit. They have or had challenges getting used to digital hearing aids, and are never super happy with whatever frequency response in the hearing aid you give them. Maybe they belong in the large group who are candidates for slow compression.
How do you recognize these slow compression candidates? There is no simple clinical test. It can be suggested that if the dynamic range is really small and there is a lot of recruitment, fast compression remains your first approach. But if a patient is looking for optimal speech recognition in quiet and in noise, and if there is enough residual dynamic range (the MPO can be set at the prescribed MPO or higher, based on the pure tone audiogram), slow compression is worth a try.
How many patients are candidates for slow compression? The jury is still out on this one. Existing scientific literature and anecdotal information is not conclusive. But I would not be surprised if it turns out to be that for every two patients that require fast compression, there is one who needs slow compression. Like ballroom dancing: quick, quick, slow.
With Naída B, Phonak offers you the choice between slow (Adaptive Phonak Digital Contrast) and fast (Adaptive Phonak Digital) compression. The slow compression variant comes with a brand new MPO calculation that may help when the slow compression causes the limiting system to be reached earlier than with fast compression. This is an essential new piece to the puzzle which was not available previously. The choice in compression speed gives you more fitting flexibility to address a patient’s individual needs, without having to go to a different hearing aid, which is always cumbersome.
When your compression speed effectively addresses your clients’ needs and preferences, put on your dancing shoes and …. Life is On!
To learn more about severe to profound hearing loss and what Naída B offers, watch this short video:
1 Bor, S., Souza, P., & Wright, R. (2008). Multichannel Compression: Effects of Reduced Spectral Contrast on Vowel Identification Stephanie. J Speech Lang Hear Res, 51(5), 1315–1327.
2 Souza, P., Wright, R., & Bor, S. (2013). Consequences of broad auditory filters for identification of multichannel-compressed vowels. Journal of Speech, Language, and Hearing Research, 55(2), 474–486.