Live Speech Mapping

Hearing Correction

 

At Advanced Digital our advanced audiometric technology allows us to simultaneously view the results of your hearing test on a computer screen while programming your hearing instruments in real-time as you listen. The system has a unique feature called “Live Speech Mapping” that will actually show you how much speech sound is reaching your eardrum. Each ear, each hearing instrument, and each hearing loss is uniquely different. Our technology allows us to more accurately take these considerations into account.

 

Some of the accompanying benefits of this process are:

 

• Acoustically accurate hearing aid fittings.
• The ability of the patient to hear first hand what the new digital technologies can do to aid their hearing loss before investing in hearing instruments.
• The ability to quickly gain a greater understanding and appreciation of the new digital hearing aid technologies.

Advanced Audiometric Technology

Several patients have requested that we provide a glimpse of the technical aspect of hearing correction available at Advanced Digital. Almost without exception we hear from our patients the same comment, “That was the most thorough explanation of hearing correction I have ever heard. Nobody has ever explained it to me like that before”.  So, for all our more technically minded friends, we are providing a somewhat brief and rather narrow sketch of the “Live Speech Mapping” and fitting verification process that our patients have found so fascinating. The example below assumes the patient has been determined to be a candidate for amplification and several other factors have come to bear on the amplification selection and fitting process (i.e. physical anatomy, lifestyle requirements, dexterity, etc.)

 

One of the primary goals of hearing correction by amplification is to utilize to the greatest extent, a patients residual hearing capacity, by delivering speech sounds, digitally tailored, to the patient's ear drum. Furthermore, these digitally tailored speech sounds should allow soft sounds to be audible, speech sounds to be comfortable, and loud sounds to be loud, but not uncomfortable.

 

In order to accomplish this we need to identify the frequency and intensity of speech and their relation to a patient's specific hearing loss. This can be done by using a "speech canoe" overlay on a patient's hearing exam, commonly referred to as a audiogram.

 

The International long-term average speech spectrum, or "speech canoe" represents the area of frequency and intensity in which the energy in average English speech occurs for a normal hearing person. This is measured at a slightly raised voice (70dB) at one meter.  The most common speech sounds in English are then plotted onto the "speech canoe" on the Audiogram.

 

Below is an audiogram with the "speech canoe" overlay.

The "speech canoe" overlay is a useful tool in understanding the effects of hearing loss with regard to understanding speech. The speech canoe displays those areas which are the most important for speech recognition. If the Audiogram (test result) values are located entirely above the "canoe", a 100% word recognition score is predicted. When some of the hearing level values lie within or entirely below the "canoe", the predicted speech recognition scores are reduced. The speech canoe illustrates the specific speech sounds, which can and cannot be heard, depending on an individuals hearing loss.

Below is an example of a patient's audiogram which predicts "normal hearing", or a range of hearing that is at or above 20dB on the audiogram. The red line with red circles indicates the point where the patient can just hear a pure tone at each specified frequency in his right ear. A blue line with X's would indicate the results for the left ear.

If the hearing test produced values below 20dB (the yellow line) some degree of hearing loss would be indicated.

Now let's look at a hearing loss and its relationship to the speech canoe. The audiogram below shows test values below the 20dB level. The low frequency hearing loss is mild and you can see that many of the low frequency vowel sounds in speech are still audible to this patient at normal conversational levels. However the hearing loss in the high frequencies is such that most of the high frequency consonant sounds of speech are inaudible to this patient at normal conversational levels.

 

This patient can hear people talking (low frequency, vowels), but cannot hear people clearly (high frequency, consonants). His common complaint is that people do not speak clearly - they sound like they are mumbling. He also likes to listen to the TV with the volume at least 20dB higher than his normal hearing family members. 

Now the question becomes, "what can amplification do to help with this sort of hearing loss"?

 

This patient is a very active 77 year old retired engineer with a doctorate in mathematics. His hearing demands are high and he wants to, "get the job done" with regard to hearing the best he can.

 

After discussing the various options available, this patient chose to be fit with a pair of Phonak MircoPower aids.

 

The aids where initially programmed and fit to the patient. Programming adjustments where then made while the patient wore the aids during the fitting verification using a process called "live speech mapping".

 

Live Speech Mapping (LSM) uses live speech as the input signal for measuring the Aided Response in Real Ear Measurements (measurements made at the ear drum). This method is used because speech is the primary signal of interest and the most important sound the hearing instruments are required to process.

 

How it works

 

Speech input is measured by a probe microphone that is placed in the ear canal while the aids are in place and turned on. Information is displayed in “real time” as a continuously updating peak curve from 125Hz to 8kHz. The measurements can be directly compared to the patient’s Audiogram values (hearing test results), and their relationship to a modified aided speech spectrum “canoe”. (The speech “canoe” for normal speech is modified to represent the amplification requirements necessary to provide the proper listening level for normal speech, given the patient’s specific hearing loss.)

 

The live speech input level is monitored in real time with a reference level meter on the display. Louder and softer input levels are obtained. During testing, a peak curve representing the maximum speech sound reached at each discrete frequency over the duration of the live speech input appears on the screen. This detailed information is useful in programming the gain and compression of the hearing instruments for soft, moderate and loud input levels.  Correctly programmed hearing instruments will produce digitally tailored speech output within the boundaries of the patient's residual hearing capacity for soft, medium and loud input levels and self adjust to provide the correct amount of amplification for the listening environment, without the need to continually adjust a volume control.

 

The live speech mapping diagram (shown below) differs from the audiogram in that the soft sounds are at the bottom of the graph and the loud sounds at the top. The modified speech canoe is the shaded area which represents the required level of speech sound amplitude that must occur at the ear drum of this patient for him to hear. The three different lines indicate measurements at soft, medium, and loud levels. As you can see the frequency response of these instruments are a perfect fit for this hearing loss according to this procedure. Post fitting adjustments can be made to further tailor the acoustic fit according to the patients subjective preferences.

Results for the right ear were equally impressive. This patient reported greater benefit and better hearing with the Phonak MicroPower instruments than any of his previous instruments.

 

Properly selected and programmed digital hearing instruments can provide hearing correction previously unobtainable 5 years ago. Contact us for more information.