By Marshall Chasin
Originally posted on hearinghealthmatters.org On June 20, 2017. Reprinted with permission.
I am always surprised by how the various hearing aid manufacturers lump the two words “speech” and “music” together in one sentence…. “Hearing aid X can help with speech and music, and can help you jump higher and run faster….”. Of course, everyone knows that the last part is true and many of my hard of hearing clients can leap tall buildings in a single bounce. But lump “speech” and “music” together in one sentence??!!
In many ways, the construction of speech is much more-simple than that of music. I am fond of saying that speech is sequential and music is concurrent. Speech is one speech segment followed by another in time. There are some overlaps which speech scientists call “co-articulation” and some assimilation of one speech sound with an adjacent one and linguistics would refer to this as being governed by “phonological rules” but in the end, speech is characterized by either lower frequency vowels and nasals (sonorants) one moment and possibly higher frequency stops, fricatives, and affricates (obstruents) the next moment. Speech does not have both low frequency sounds and high frequency sounds at the same time. It is like playing the piano keyboard with only one hand – you are either playing on the left side, the middle, or the right side, but never both sides at the same time. Speech is sequential – one sound at a time followed by another sound, a moment later.
Music is concurrent; unlike speech, we must have both low frequency sounds and high frequency sounds that occur at the very same time. Musicians call this harmony. Even while playing a single note on the piano keyboard, there is the fundamental or tonic – the note name that is played – and then integer spaced multiples of that note spread out on the right-hand side of the piano.
Music cannot be like speech, one frequency region at a time. And speech cannot be like music, many frequency regions at a time.
Graphs that compare music and speech are simplistic; they should not be used to define amplified frequency responses or the characteristics of compression circuitries. They look pretty but have very limited value.
Graphs such as this are useless.
Algorithms that have been optimized for hearing speech need to be different than those that are optimized for listening to music. Even something as simple as feedback management can be quite useful for speech but disastrous for music. Imagine a feedback management system that confuses a high frequency harmonic for feedback – music would essentially be shut off. Ad hoc features such “only restrict the feedback manager to sounds over 2000 Hz” would be slightly better than feedback managers that are active in all frequency regions, but even then, the higher frequency harmonics of the music would be nullified.
Another algorithm that has shown itself to be of great assistance with speech is frequency transposition or frequency compression. These phrases are meant to apply to the wide range of frequency shifting algorithms that are available including linear and non-linear shifting and compression. Imagine the second or third harmonic of a note being moved elsewhere. Discordance will result.
The best music algorithm for severely damaged cochlear regions would not be to transpose away from that region, but simply reduce the gain in that frequency region. A creation of additional in-harmonic energy where it is not supposed to be will ruin music.
And indeed, in most cases of algorithms for amplifying music, less is usually more. Turn off the fancy stuff and just listen to the music. Wider or narrower frequency responses have nothing to do with the input source- music or speech- and as such should not be different between a “speech in quiet” program and a “music” program.
About the Author
Marshall Chasin, AuD, is an audiologist and director of research at the Musicians’ Clinics of Canada, Toronto. He has authored five books, including Hearing Loss in Musicians, The CIC Handbook, and Noise Control—A Primer, and serves on the editorial advisory board of HR. Dr Chasin has guest-edited three special editions of HR on music and hearing loss (August 2014, March 2006, and February 2009), as well as a special edition on hearing conservation (March 2008). Correspondence can be addressed to: firstname.lastname@example.org