Thursday, January 21, 2010

FREQUENCY RESPONSE: WHAT FREQUECIES ARE YOU MISSING?

Band Hearing Test 7 by slhsphoto.




a hearing evaluation doesn't hurt
but it can help - A LOT




“I Can Hear That,
But I Can’t Hear This.”

When most people experience hearing loss, we don’t lose hearing across the entire sound spectrum – from high to low frequencies.

More typically, we lose our ability to hear certain frequencies. Let’s go back to science class for just a second to provide some background on the latest in hearing tech.

What is Sound Frequency?
If you harken back to those good ol’ high school days, you might remember a lesson or two on sound but if not, let’s recap.

Let’s use an orchestra as an example of sound. Sound travels through the air in waves, so when the maestro strikes up the band, air is disturbed, sound waves travel through the air, reach your outer ear – the pina – where these sound waves are channeled into the ear canal for processing.

But, not all sounds are the same. Sound is delivered to the ear at various frequencies. Back to the band: the twitter of the piccolo sounds very different from the low, mellow tones produced by a bassoon, right? So, with good hearing, we hear the high pitched instruments and low-pitched instruments – sounds across the frequency spectrum.

Hearing loss often occurs within specific hearing frequencies. Example? Patient A may experience hearing loss in the upper frequency ranges – the piccolo or cymbal range. Patient B may have lost hearing in the mid-frequency range – violins, trumpets and other musical instruments that produce sounds in the mid-range.

And finally, some of us hear high and mid-frequencies no problem. However, we may not pick up the low thump of the bass or kick drum. These low-frequency sounds simply don’t get processed.

Speaker output, from your stereo rig, is measured in frequency response and the higher the quality of speaker, the greater the frequency response.

Just remember, sounds travel in waves. The higher the pitch, the more waves per second reach your hearing mechanism. Lower pitched sounds produce fewer sound waves per second. It’s this frequency response – the ability to hear the highest highs and the lowest lows – that hearing aid technology strives to reproduce.

The fact is, however, that nothing will replace the hearing nature gives us. But, after a thorough hearing evaluation by an audiologist, hearing aid practitioner or other hearing professional, you (and your partner in better hearing) will be able to pinpoint those frequencies where you’ve lost hearing and those frequencies where your natural hearing is just fine.

So, your hearing loss is different from mine and his and hers. And during a hearing evaluation, the hearing health pro determines which frequencies are causing problems for you.

Simple, right?

“What’s the Frequency, Kenneth?” – R.E.M.
The objective of a hearing evaluation and the fitting process is to deliver hearing across the broadest frequency spectrum – from the highest highs to the lowest lows. Unfortunately, that’s easier said than done.

For example, those with high-frequency hearing loss require more powerful hearing devices to boost those higher frequencies. The tricky part is providing the juice without creating a feedback nightmare. The more powerful the ear amp, the more challenging it is for designers and manufacturers of hearing aids to eliminate feedback and other issues associated with that extra oomph.

Further, even the best hearing aids have limited frequency response so high-frequency hearing becomes a technical problem, as well. Combine the functional problems, i.e. brain-busting feedback, with the technical limitations of today’s hearing aids and you start to get a feel for the problem.

Frequency Lowering
So what’s a music lover to do? Well, the hearing health community is looking at something called frequency lowering. With frequency lowering, unhearable high frequencies are converted to a lower frequency – one that can be picked up by the hearing device and one that can actually be heard and used by the hearing aid wearer.

Example: let’s say you have incoming sound in the 4000hz range. Using frequency lowering – non-linear frequency compression as the professionals call it – those 4000hz sound signals are compressed into 2000hz sounds, within the hearing range of both the hearing aid and the hearing aid wearer.

Now, it’s important to note that the 2000hz signal doesn’t restore the ability to hear at 4000hz, i.e. you still don’t hear the piccolo – at least not in its original form. But you can “hear,” interpret and act upon sound information that would otherwise be out of hearing range.

Where Do I Sign Up?
First, learn more about the process and the results. The American Speech-Language Hearing Association has an easy-to-understand article on both hearing compression and hearing transposition – the two methods used to create usable sound for those with moderate to severe hearing loss.

Sound compression is just what it sounds like. High frequencies are squashed down (compressed) to lower frequencies that can be heard. Sound transposition actually electronically moves higher frequencies into hearing range. Using this technology, lower frequencies don’t have to be compressed along with higher frequencies. Studies and evaluations on both sound compression and transposition continue but the good news is the technology has come to market in one form or another.

Phonak has a long-standing, industry-wide reputation for both innovation in design and quality in the manufacture of hearing aids. The company’s foray into transpositional hearing is Naída, a high-boost unit that employs transpositional tech rather than compression technology.

For this reason, Naída is the ideal solution for individuals with good quality low-frequency hearing but drop off quickly in the higher frequencies. Because the higher pitched sound is digitally “moved” to a lower frequency, the wearer can still hear the full range of lower frequencies without compression dropout. In other words, you still hear the bass line naturally while higher frequencies are processed into lower, hearable and useable sound information.

Users of Nadía report a dramatic improvement in hearing. As one wearer described it, “I hear things in a different way.”

Using nonlinear frequency compression technology (indeed, a mouthful), people with moderate to severe hearing loss are able to better utilize high-frequency sound – a benefit that these long-time hearing aid wearers appreciate to the fullest.


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