The first of many technical innovations- part 3 of 7

Live Music Plus from Bernafon and the Dream/Unique circuits from Widex:

As discussed in part 1 of this blog series, there is a “front end” problem with digital hearing aids that limits their usefulness with the higher sound level inputs that are characteristic of music.  In part 2, some clinical strategies were discussed to improve a hearing aid for music- that is, how can you make a hearing aid that someone already has slightly better for listening to and playing music.  In this third part, the first technical innovation to resolve this problem, from Bernafon, and later by Widex, is discussed.

These approaches that Bernafon and Widex take to accomplish this are slightly different, and I apologize if I haven’t got all the technical details quite right.  However, since these technologies are now several years old, readers can contact your audiologist for a more complete explanation, or the manufacturer representative if you are a hearing health care professional.

The front-end problem can be thought of as a low-hanging bridge.  One either needs to duck under the bridge or raise up the river to the level of the bridge, or, in the case of Bernafon, go around the bridge.  First the technology of Bernafon will be discussed, then Widex’s technology.  Both work quite well with music (and speech) and have both essentially the problem quite well.

Bernafon Live Music Plus circuit:

Now available on both Bernafon’s 7-series and its 9-series hearing aids, the concept of Live Music Plus is based on the definition of “dynamic range”.  The dynamic range is the range in decibels between the quietest sound level that can be transduced and the highest sound level that can be transduced.  The limit on the high end is the analog-to-digital (A/D) converter, and the limit on the low end is the microphone noise (as well as the individual’s hearing thresholds in the lower frequencies–below 1000 Hz).

With typical 16-bit architecture of modern hearing aids, there is at best a 96-dB dynamic range.  Sounds outside of that range simply cannot be transduced through the A/D converter and no amount of software programming (that occurs later in the system) can resolve this front-end distortion.  More often than not, the effective dynamic range is on the order of 90-92 dB because of engineering design issues that need to be met.  In any event, the dynamic range is a function of the number of bits (16 bits).

Note, I was not being sloppy in the last paragraph by not specifying dB SPL- I merely said 96 dB.  The dynamic range is indeed, just a range, and it can be 96 dB going from 0 dB SPL to 96 dB SPL, or, 50 dB SPL to 144 dB SPL- still a 96-dB range.

In the case of the Live Music Plus program from Bernafon, the range is shifted to 15 dB SPL to 111 dB SPL.  That is, the entire range has been shifted up by 15 dB, since there really isn’t much music (or speech) energy below 15 dB SPL.  This does (nominally) increase the noise floor of the hearing aid, but as a clinician with near-normal hearing,  I have never heard it and none of my clients has ever reported hearing this slightly elevated noise floor.

The advantage of this higher 96-dB range (15 dB SPL to 111 dB SPL) is that the A/D converter is more optimally set to handle the higher sound level (and peaks) that are characteristic of music.

I have used this circuit setting on hundreds of musician clients over the last 7-8 years and it works very well.  More on the technology about Live Music Plus can be found on Bernafon’s website.

Widex Dream circuit:

This is a newer approach that seeks to use a clever technology to allow the higher sound level inputs of music to be transduced with minimum amounts of distortion.  This technology is available on all Widex  levels ranging from the 110 up to the Widex Dream 440 circuit.

This approach uses a transformer approach that has the ability to increase the high end of the dynamic range to 113 dB SPL as opposed to their older approach (Clear circuitry), which had a 102 dB SPL limit.  A stated advantage of the transformer approach is that the noise floor does not increase- the upper end is merely elevated.

I am not sure if this difference in noise floor between the Bernafon and the Widex approaches is clinically significant, since microphone and other noise floor issues do not appear to be audible to my musician clients.

The following figure is from a study that I performed in my clinic (for which my clinic received funding from Widex).  In this study the older Widex Clear circuit was compared with the newer Widex Dream circuit, but all other differences were maintained; the only difference was that the Clear circuit could only handle up to 102-dB SPL level inputs without distortion whereas the Dream circuit could handle input levels up to 113 dB SPL