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Hearing Aids and Music: Interview with Marshall Chasin, AuD

Hearing Aids and Music: Interview with Marshall Chasin, AuD

August 20, 2009 Interviews

Douglas L. Beck, AuD, speaks with Dr. Chasin about hearing aids and music, in-ear monitors, differences between speech and music, protecting ears, time versus intensity, and temporary threshold shift.

Academy: Hi, Marshall. It’s great to be with you again.

Chasin: Hi, Doug. The pleasure is mine.

Academy: Marshall, I was hoping to speak with you about your new (2009) book, Hearing Loss in Musicians: Prevention and Management.

Chasin: Excellent. It’s one of my favorite topics!

Academy: The book is filled with practical chapters and useful information from the basics of hearing and ear-related anatomy and physiology, to headphone use, hearing protection, acoustics, hearing aids and music, in-ear monitors, and more. It’s very well done and really quite useful.

Chasin: Thanks, Doug. That’s very kind.

Academy: Marshall, it seems very simple to say that if we just lower the loudness by 3 dB, based on the “time vs. intensity” trade-off, we lower the risk of hearing damage by 50 percent. So why is it so difficult to get people (and musicians in particular) to protect their hearing?

Chasin: Well, you’re right. It really is simple, and a 3 dB reduction does reduce the risk by half. Unfortunately, even though humans are very good at determining and measuring frequency, we’re not very good at determining loudness, or differences in loudness. For instance, remember the old SISI test (Short Increment Sensitivity Index test)? It showed humans can better tell differences at higher levels than at lower levels. But, given a noisy environment with lots of musical instruments playing simultaneously, if we drop the loudness of the band or orchestra by 3 dB, nobody would notice and it would be much safer for longer periods of time. So, if we can get people to turn it down slightly, something along the lines of a music-based just-noticeable-difference (JND), we’d make significant progress.

Even for non-musicians, listening to their MP3 players, mowing their lawns, using hair dryers, driving around with the music cranked-up, their noise exposure adds up. Nonetheless, if we can drop our “normal” listening levels by 3 dB, we can double our listening duration, without adding significant risk.

Academy: That’s a really good point, Marshall. I think audiologists (and parents of teenagers) often try to promote soft and medium listening levels, and although that would be clearly best for our ears, a 3 dB reduction seems much more achievable and sustainable!

Chasin: I agree. It may be wiser to go for a little important change, rather than a wholesale change in loudness. In particular, musicians can achieve significant lowering of loudness through strategic changes, such as moving the amplifiers or instruments to decrease direct exposure to sound and by listening strategically. For example, if a musician plays a very loud venue one night, it’s best to let the ears rest, usually 16 to 18 hours. In other words, don’t mow the lawn or do target shooting the next morning! Let the ears recover before the next loud sound exposure. Specifically, if possible, let the TTS (temporary threshold shift) resolve before the next significant sound exposure.

Academy: Yes, great point. In fact, in your book, you note many key points, but among them, two are germane here. The first is whether the 3 dB or 5 dB exchange rate (time vs. intensity) is more appropriate (although the evidence seems to support the 3 dB rule), and the second is that TTS is a necessary precursor to PTS (permanent threshold shift).

Chasin: Musicians and non-musicians would be well advised to take note of both of those points, and indeed, discussing both points with their audiologist would be an excellent idea. There are two mechanisms of TTS (per Don Henderson); necrosis and/or apoptosis. In TTS, the tip of the outer hair cell can become disconnected from the tectorial membrane—and then it can re-attach which would re-establish the previous hearing threshold, and the other mechanism is glutamate ototoxicity. Glutamate is a neurotransmitter substance released in response to sounds, and when there are high levels of glutamate, glutamate becomes toxic and it takes some 16 to 18 hours to fully resolve in the ear.

Academy: Okay, very interesting work. Moving on, John Chong’s chapter (chapter 13) was a lot of fun to read and very interesting. I was amazed to read that Beethoven created over 120 hours of music across his lifetime—that is absolutely remarkable. As best I recall, the Beatles entire studio library was less than 10 hours.

Chasin: Well…,those are interesting numbers, and they sound about right, but I can’t comment as to their correctness other than to say John is a stickler for detail! John’s chapter offers some new and exciting ideas such as how musicians experience occupational Darwinism, or “survival of the fittest” and how the injured musician is often left behind or replaced. With due consideration of Beethoven’s vast library of music, while apparently having severe-to-profound hearing loss and severe depression, it’s absolutely startling. And, if we consider musicians to be “acoustic athletes,” Beethoven was clearly of Olympic caliber. John’s chapter is very interesting and insightful.

Academy: What about the differences with respect to hearing aids for speech versus music? In particular, for speech, the most important sounds are above 1,000 Hz, whereas for music, the majority of all sounds, particularly the fundamental frequencies are below 1,000 Hz.

Chasin: Yes, well these are very important differences in spectral content and they are very important for the hearing aid wearer to understand. Particularly, because hearing aids are essentially made to amplify speech sounds. Speech is arguably the most important thing one can listen to—and that’s why hearing aids are generally maximized for speech sounds.

Doug, you and I have previously discussed that for most musicians and vocalists, hearing aids are usually not needed and indeed, hearing aids may be detrimental for live performance and practice sessions. I think this is a key point. Musicians and vocalists generally need to make sounds softer, and therefore, hearing protection is the better choice, rather than amplification. For non-musicians who enjoy listening to music, the key is often to listen at a comfortable listening level, adjusting the volume control on the home stereo or MP3 player.

If one really needs to listen to music through a hearing aid, many of the circuit options that are advantageous for speech are not useful, and may be disadvantageous for music. The hearing aid wearer is best advised to speak to their audiologist with his or her particular needs and concerns and to perhaps have one program set aside for music. The music program might include very low gain, essentially linear settings and no compression and no other automatics (such as directionality or noise reduction). Of course, compression is a very important and phenomenal advantage for speech, but it can easily be disadvantageous for music. So the bottom line is…I prefer people don’t wear hearing aids when listening to music—it’s rarely necessary, and if it is necessary—better to not mess up the speech program, but set aside a dedicated music program.

Nonetheless, speech and music do have many similarities; they’re both generated by a vibrating source and they convey emotion and information via moving molecules, but the output can be highly variable. In speech, we call it phonetics and in music it’s just called the spectrum of music. As you said, Doug, music has a lot more low frequency energy than speech. The audiologists reading this know we test hearing (traditionally) from 250 to 8,000 Hz. Importantly, “middle” C is 256 Hz, and so it is apparent that as audiologists and diagnosticians, we basically ignore the entire left side of the keyboard! And then we only go up to about 4,000 Hz on the right side of the keyboard (4,186 Hz for the purists!). Of course we don’t do it maliciously, but we do it because sounds below 250 Hz have little diagnostic value with regard to a differential diagnosis, and the sounds below 250 Hz have little to do with speech perception—so music perception and speech perception are very different. Importantly, hearing aids are not meant to transduce the very low frequencies as those sounds are quite a bit less important for speech perception. Further, hearing aids usually incorporate vents, and so the very low tones can enter the ear through the vent relatively unobstructed. Although we know a lot about speech perception and preferences, we know relatively less about music perception and individual preferences.

Academy: What about loudness and dynamic range in speech and music? Cold running speech typically has a 30 dB dynamic range, whereas music can easily have a 100 dB dynamic range.

Chasin: Well again, music is much more dynamic than speech. The loudest component of shouted speech is perhaps 80 to 85 decibels, when vocalizing the vowel /a/. Higher frequency consonants almost never exceed 60 decibels. In contrast, very quiet music often exceeds 80 to 85 decibels and loud music might approach 110 to 115 decibels (dBA) and perhaps some Wagner pieces may be even louder! Even though speech is very complicated, it is well defined. This is in contrast to music that is quite variable with regard to loudness and spectral components.

Academy: Okay, Marshall, I know we can talk about this stuff for hours, but I also know I have to let you get back to the clinic!

Chasin: Thanks, Doug. It’s been a pleasure for me and lots of fun.

Academy: Thank you, too, Marshall. I think the book is excellent and I recommend it whole-heartedly. I learn something every time we get together. One last note, I know you have graciously allowed us to reprint pages 153 through 161 from the book. These pages include:

Note: These pages are free to download and can be photocopied and distributed for non-commercial purposes. Courtesy of Marshall Chasin. Additionally, these pages can be found at www.musiciansclinics.com.

Marshall Chasin, AuD, MSc, Reg. CASLPO, Aud(C), audiologist and director of Auditory Research at Musicians’ Clinics of Canada, Toronto. Dr. Chasin’s book, Hearing Loss in Musicians – Prevention and Management, is available through Plural Publishing (www.pluralpublishing.com).

Douglas L. Beck, AuD, Board Certified Audiologist, is the Web content editor for the American Academy of Audiology.

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