Raising the headroom bridge
A common complaint with hearing aid users involves distortion or “clipping” that comes with high-volume sounds. Luckily, a solution is on its way and it involves one thing: headroom.
September 05, 2013
Headroom can be defined as the “residual dynamic range of a hearing aid, expressed as the difference in dB SPL between a given output (such as gain at user settings) and the level of saturation of the device”*. In layman’s terms, it’s the amount of sound that a user can hear through his hearing aid before clipping or distortion occurs.
“It’s the range between the softest elements that can be transduced and the highest ones,” says Dr. Marshall Chasin, Director of Auditory Research at the Musicians' Clinics of Canada. “With modern hearing aids, the ‘limited headroom’ problems really refer to the hearing aid’s inability to transduce intense signals such as music.”
The distortion problem
For this reason, increased headroom in hearing aids can especially benefit musicians, who are regularly exposed to fluctuating sound levels. If headroom is too low, says Chasin, louder components of music can cause distortion that often can’t be cleaned.
Ironically, modern technology caused this problem, rather than fixed it. Chasin says that 1980s-style analogue hearing aids didn’t have clipping. Distortion instead came with the transfer from audio to digital signals.
“We have all seen pictures of trucks or double-decker buses having their roof taken off when trying to pass under a low-hanging bridge,” says Chasin. “Music is also like this. There is no benefit for a ‘music program’ if the front end ceiling is set too low.”
The natural solution
Chasin stresses that increased headroom isn’t just important for professional musicians. It’s for anyone who wants to listen to music. A person’s own speech can also cause distortion if volume levels are too high. With current hearing aids, one way to combat this distortion is to turn down the volume on the input sound, like a stereo or television, and turn up the volume of the hearing aid. This effectively allows a hearing aid user to “duck under” the headroom bridge and avoid the distortion. But it doesn’t give the most natural or comfortable sound.
Another solution to the problem includes creating microphones that are less sensitive to lower frequency sounds, which fools the recorder into thinking it’s receiving a signal that’s within its operating range. But again, this solution means a more artificial and less transparent sound.
No hearing aid can claim a limitless ceiling, but a new generation of digital hearing aids comes pretty close. These devices effectively raise the level of that “low-hanging bridge” and create increased headroom and a more transparent sound. These hearing aids take the 95 dB limit of modern hearing aids and shift it up to 111 dB SPL, a limit that can provide clear sound in almost any environment.
A new generation of hearing aids raises the headroom bridge for the most clear and transparent sound yet.
* Stach, Brad A. Comprehensive Dictionary of Audiology, Illustrated. Clifton Park, NY: Thomson/Delmar Learning, 2003. Print.