Hearing Loss…after "A Soundman's Biggest Nightmare."

By Jim Sorensen

There has been a sort of intriguing dichotomous relationship between our hearing “test gear” and our other “test gear”…you know, the stuff that says TEF and HP and Tek on it.  There is perhaps a greater dichotomy between those two, together, and the modeling software that’s supposed to make it possible for our hearing apparatus to do its job most proficently in a way that relates to the outer world.

It’s sort of interesting that this gets into that adage about the guy with two watches not being able to tell the time with any sort of accuracy.  We have two sets of test gear…our ears and brain, and the TEF, HP and Tek boxes.  Can we tell anything useful from all of this together?

For generations sound teachers, like Don and Carolyn, Pat and Brenda, and numerous others…I mention these only to suck-up…who insist that you use the necessary science to design systems and specify “fixes” for rooms in addition to the very important bit about “listening” to the room, too.  (Oh, yeah.  sorry about the “generations” thing, guys.)

They all meant that if the room still sounded bad when you finished you had either made a mistake with the test gear and the prescribed fix or you had a hearing problem.  By the way, kudos on a statement that highly clarifies the problem…since the problem is to allow for human hearing to take place efficiently.  It’s not to build a sound system, that’s one cure but it’s not an end goal.

Anyway, the dichotomy comes in when you realize that your on-board test gear is modifying the data before you’re even aware that you have the data.  Here’s how to see what I’m talking about:  Take a pocket recorder that’s got good bandwidth and a quality loudspeaker and record  conversations in a room.  At the same time, make notes of what was said and what you heard.  Note what you heard as “anomalies” in the room…things like reverb and echo.

Now play the recorded audio back and do the same thing with what you’re listening to.  Even if you took the recorded into an anechoic room for playback, you’d still hear all kinds of things in the recorded audio that you don’t recall in the live tests.  Obviously this has to do with time and it’s your brain processing the audio in real-time that essentially ignores all the “chaff” in the live audio so you can understand it better.  The recorder doesn’t do that and once you break the time synchronization you can easily detect the presence of the “extra” audio.

Think of it this way, ancient man needed to use his ears to detect things “that go bump in the night” and in the woods around him so his ear-brain link learned to focus on the important stuff and ignore the extraneous noises.  He’d hear the soft “snurfling” of a tiger and not the constant din of the crickets and frogs.

In a sort of existential way this example tells us that we really can’t trust our ears…they’ve been “jiggered with”…but we can learn to work with that jiggering.  It’s like any form of pre-distortion…if you know it’s there and can describe it you can make a “filter” that will undo it.  It’s done all the time in technology.  One grand example is the addition of capacitor banks to high power transmission lines to swamp out some of the inductive reactance that you’ll find on really long wires.  These get the current and voltage lined up properly again reducing the “distortion” and lowering losses.  Same in phone lines, if they’re still analog.

A more familiar example for us older duffers is the RIAA curve on records.  This reduction of the LF and boosting of the HF was done on the recorder end partially to reduce noise and partially to get the little signal squiggles to fit in a realistic “width” on the record surface…a width that the stylus could track in without banging into other squiggles or running out of mechanical room.  The opposite filter in the phono-pre-amp restores (sort of) the energy balance by boosting the LF and attenuating the HF hoping that the sum of the two filters would be “null” to allow for playing back a record so it sounds right.  I once owned a pre-amp that had a selection that let me shut off the RIAA filters and my records all sounded…”bright.”  Yes.  That’s the word…”bright.”

Is the “data” on the record correct?  No.  It’s been jiggered but it’s been jiggered in a way that’s calibrated and understood so it can be put back together correctly when it’s needed.

Relating to our ears, we can see that if we understand that what “we hear” as individuals is strictly ours and no one elses we can see how we can relate our personal hearing ability to good sound…if we have a benchmark.  A personal note:  If I think that the PA system is a little bright, it’s probably not but I know that and expect a well adjusted system to be…what did Mackie call it?  “airy?”

This is about setting a “personal” standard…like a personal best in some athletic event…not about correcting your ears to be “perfect.”  (I don’t know what that means.)  Anyway, here’s about where the stuff with the boxes marked TEF and HP and Tek comes in.

If we set up a room to meet the “standards” of  “perfect” sound and measure it and listen to the room and then go to a different room and set it up so the test gear reads the same and, to us as individuals, the room “sounds” the same, then we can say with some assurance that we have closely replicated not the room but the “sound” of Room A in Room B which was our job.

It’s important to remember that the standard is based upon a couple of things.  First is the measured capability of most humans…approximately 20 Hz through 20 kHz…to detect moving air in a way that relates to “sound.”  Thus, the two become conjugates and we can use the term “moving air” interchangeably with “sound.”  Not very practical, but you could do if you wanted people to look at you funny.  It’s also based on the idea that the mechanical test gear (HP, Tek, TEF, etc.) can correctly relate that measured capability to the laws of science in matters like air pressure and charge.

In testing a room we look at the test gear and measure to see if we meet the “specifications” derived from what we think that the room should do, if you will, the theoretical or predicted model.  If we predicted that the room would have an RT60 of 0.5, to use only one parameter, and the test gear agrees that it does, then we can listen to the room and say, again with reasonable certainty (within the confines of that single parameter,) that what we’re hearing should sound exactly like that if we placed the same transducer in an identical place in an identical room which measured the same way.

If we train our ears to “know” these comparisons, then they are useful to us as tools and this is part of where our ears are like VU meters.  The VU meter is a Volume Indicator (VI…remember the other article?) that reads in dB and ostensibly measures audio power.  It doesn’t really because there’s no convenient way to directly measure power so it really displays the resultant of a “variable” against a “known” which resultant we can call “power” if we want to.  The same with our ears.  They really only react to air pressure and it’s that vibrating air pressure that we call “sound” and it’s what our brain has been trained to report as “sound” when our ears react to air pressure changes.

In this case, there is no problem with having a hearing aid, it’s (hardly simply) a matter of re-training your ears to “know” what a room with certain characteristics should sound like AND being able to recognize when your own hearing has changed to distort the “data” your ears collect so other corrective measures can be taken.  You could take the position that something like ear-plugs were sort of an anti-hearing aid.  If you put in ear plugs and go to the concert you will still hear things but differently.  In a little while, your ear-brain link will “fill in the blanks” on what the plugs stop and you can enjoy the music.  The same with hearing aids…in a while you will “fill in the blanks” and even if you never again hear specific frequencies you’ll be able to use your ear-brain link not only for pleasure but for work.

In large measure, most of us need to work on thinking in terms of, and accepting, “identity.”  Another example:  Can you use a screwdriver to open a paint can?  Sure you can but is it the correct use for a screwdriver?  No it’s not, but you can do it and justify it by setting as a condition that “opening the paint can” is the goal, not “correctly using a screwdriver.”  If you took a course in “paint can opening” you’d get an A, if you took a course in “correctly using a screwdriver,” you’d get an F.  Both for the same action.

When that logic is applied to hearing and hearing aids you can see that the goal is not to hear perfectly but to hear usefully.

Perhaps by considering that our ear-brain link is an important piece of test gear in our tool box and by recognizing that ALL test gear must be calibrated and “re-calibrated” from time to time we can see that even though we don’t hear the way we did and perhaps as well as we did, we still can use the ear-brain link in that all-important “tool” capacity.

A final note:  Most of the “standards” which we use are derived if not still firmly nails to artibrary things literally like the length of the King’s finger.  Why then do we bother with test gear calibrated down to a fraction of a dB in most cases and why do we try to tune systems to a precision of a dB?  Our ears might be able to discern a dB, most likely 3 dB and the audience perhaps 10 dB if they can get through the noise of their own existence.

It’s even sillier in RF work.  The FCC has a “standard” for instrument accuracy of 2%.  Now, I happen to own two field intensity meters…these measure the voltage level of a radio signal “in space” which are calibrated by the factory from time to time to be in the 1% range of comparison to the factory standard which is another field intensity meter which has been compared to the little “standard” antenna and signal in Boulder, CO.  (Send yours to Ray, he’ll be glad to run it by!!)

The joke is that the best accuracy you can expect in the field using all this well calibrated stuff is on the order of 10%.  Even if you use a different method than the FIM (Field Intensity Meter..clever, huh?) like a calibrated antenna, a well know distance and all kinds of things about the terrain and ground conductivity and stuff like that you will get the same approximate level of precision.  It’s nature.

I guess the over-whelming question has to be whether we should just give up and give in and let standards slacken or if we should stick to our scientific guns and try for the best.  I lean to the latter but am willing to submit the former if that’s the best I can get!  Being a good Christian child I was brought up to honor the dictate of the “House upon the rock,” as opposed to the sand.  There was also that bit about “Forbidden Fruit” but…let it pass.

My father-in-law, Dr. Bob Hahn, said it best when I discussed this with him…he’s 84…he said that his hearing wasn’t as good as it used to be but then, it never was.

That requires coffee.

Keep it out of the RED!