Compression did not begin with digital hearing aids
By Theodore H. Venema, PhD
Author of Compression for Clinicians: A Compass for Hearing Aid Fittings, Third Edition
My career in this field began in 1987 as a new audiologist at The Canadian Hearing Society in Toronto. All hearing aids were analog and provided linear gain, although a few compression circuits floated around too. These used output limiting compression, with its high knee-point and high compression ratio. The knee-point was adjustable, which in turn adjusted the maximum power output (MPO). It was a way to limit the MPO without the use of “peak clipping,” which caused distortion.
Wide dynamic range compression (WDRC) entered the scene with a cannonball splash right around 1990. The action of the outer hair cells (OHCs) was now understood by clinicians as being distinct from that of the inner hair cells (IHCs). As we all know today, the OHCs enable the IHCs to sense soft incoming sounds below around 50 dB SPL. WDRC was thus seen as a rather “intellectual” type of compression, in that it electronically sought to imitate the role of the OHCs. With its low knee-point and a low compression ratio, the focus of WDRC is to elevate the “floor” of hearing sensitivity, rather than to limit the MPO or “ceiling” of loudness tolerance. It is no coincidence that otoacoustic emissions—also known to arise from the action of the OHCs—suddenly emerged as part of clinical practice.
Compression in today’s digital hearing aids hasn’t really changed all that much from then. We continue to use both output limiting compression and WDRC. The point here is that the analog hearing aids of that time (late 1980s, early 1990s) used either one type of compression or another. Clinicians had to know their compression types because their hearing selection for any client depended on this knowledge. Manufacturer fitting software did not yet exist. Today’s digital hearing aids are programmed exclusively by software. Once the audiogram is entered through Noah, the hearing aid signal processing is automatically programmed to provide whatever compression is deemed necessary. We’ve become “dumbed down,” because we no longer have to know how to apply the compression. The manufacturer fitting software takes care of all that!
The cables, the cables, the cables…
The emergence of the cables actually began in the very late 1980s, with the first “programmable” analog hearing aids. A cable from a computer (or more often a handheld programming device) was plugged into a socket on the faceplate of an ITE or on the backside of a BTE. Adjustments were made via this “digital screwdriver.” This seemed like a really “cool” alternative to manually adjusting hearing aid settings by trimmers, trim pots, potentiometers, whatever they were called. We simply turned these clockwise or counterclockwise, in order to raise or lower the MPO, gain, low-cut, high-cut, etc. I used to laugh that if the original settings were somehow lost, one could simply set all the trimmers halfway; that way, one could maximally be only half-wrong.
Back to the cables, it is truly amazing just how many different ones exist, even for the product lineup of any one manufacturer! This issue is not at all new, and I am not the first to complain about that. I must admit to feeling a little odd though, when hanging a weird looking hook around the client’s neck with cables connected to the hearing aids positioned in the client’s ears. The next step is to sit in front of the computer, hoping and praying the manufacturer’s fitting software will read the hearing aids.
Manufacturer fitting software, fitting software, fitting software…
Fitting software emerged at the end of the analog era (mid 1990s) and flourished with the advent of digital hearing aids in 1997. Of course, with each manufacturer, the fitting software is completely different. Oh, there are some similar traits among them, but the look, the feel, the labels, and also the quirks and exceptions, are different for each manufacturer.
Digital technology and software certainly do add flexibility; they also however, invite their best friend, complexity. There are so many parameters involved with fitting now: noise reduction amounts and types, directional microphones and associated polar plots, feedback suppression adjustments, linking binaural hearing aids, and don’t forget about the battery indicator beeps! It gets better; we in separate programs, make combinations of the above-said parameters, in order to specifically address various different listening situations, such as quiet, conversations, and traffic.
Has anyone seen ANSI? Where did it Go? Sometime during the late 1990s, with the advent of digital hearing aids in 1997, ANSI slipped away. It happened in the middle of the night. Since the 1950s for hearing aids, ANSI was intended to be a measurement standard for hearing aid hardware, which consists of the microphone, amplifier, and receiver (aka speaker). Add a few capacitors, resistors, inductors (and trimmers to adjust their behaviors), and you still have nothing but analog hardware. Such was the consistency of analog hearing aids. ANSI ruled in the analog land of hardware, but now fitting software rules. Quaint concerns about OSPL90, Reference Test gain, Harmonic Distortion, and Equivalent Input Noise have almost faded from view. Today it’s all about software. Most clinicians today never bother with ANSI because they are just trying to figure out the fitting software.
The dongles and Bluetooth paraphernalia…
On a semi-annual basis, the goals and deadlines of their product management cycles dictate that manufacturers must pound out new and updated products. The cacophony of their escalating product releases has become deafening. What’s more, hearing aids now come with all kinds of dongles, Bluetooth remotes and gadgets to be used with other devices that work with the phone, television, etc. Of course, these have to be “paired” together to work with the hearing aids. Despite the best efforts of manufacturers to explain things, it does make me feel a bit like “Ted the Cable Guy.”
Clients commonly come back to the office with bags containing unused cords, boxes, television streaming devices, and dongles. It can be quite difficult to get elderly people to make sense of it all! Bottom line: Clinicians today are still constantly “putting out fires,” much like they always did in the past.
It’s obvious that hearing aids today are far better than the squealing, beige “banana-shaped” BTEs of yesterday. The disappointing thing, however, is that the rate of client satisfaction has not risen at the same rate as hearing aid development and complexity. The unwanted byproduct from complexity is confusion, felt by both clinicians and clients.
We have made amazing strides in technology, digital algorithms, and features. The downside is that it has all come at a cost, literally and figuratively, to clients and clinicians. With all the recent progress, I’m not sure clinicians feel that fittings are easier today than they used to be. I also do not believe the monetary cost of hearing aids compared to eyeglasses is at all well understood by clients. Is anyone really surprised at the recent emergence of (and governmental support for) an alternative, namely, those low-cost personal sound amplification products, also known as PSAPs?