"Jim Frohoff" <[email protected]> wrote in message
news:_jKgb.2079$[email protected] ink.net...
> Jerry, Al, Andor, Rune, Eric, Martin, Keith, BenB, "J", BenP ...

> Tests with a wide-band white noise generator are, so far, unsuccessful in
> masking the noise. Maybe it's not wide-band enough, the speakers may not
be
> good enough, or perhaps my ears just aren't responsive enough to let the
> masking noise in at the high freqs. I am doing more experiments to try and
> find out what sounds might mask the noise.


At the listed frequencies of around 11-13 kHz, you may have trouble finding
good speakers or headphones to reproduce those frequencies. bottom of the
line speakers or headphones may not generate as much sould as you're
thinking. Also there's some frequency roll off about 1kHz that naturally
attenuates sound. There are ear shape related 'holes' that naturally occur,
but I'm not sure if they exist in that frequency range and I don't have the
documentation handy to check :/ . If your frequency is in one of them, you
might have better luck with headphones than speakers.

Also to begin to achive masking, you need to approach the volume of
whitenoise roughly equal to volume of sound you're trying to mask. To
achieve full masking you will probably need to be 6-10 dB louder. In your
case this may be excessively loud. A 1/3 octive at that frequency with a
large volume is a lot of energy.

An additional complication is that your ear has coarse volume adjustment.
It acts like a broadband gain reduction on the input sound. The sound is
then broken down by frequency with a part of the ear that has roughly a
20-30 dB dynamic range (40 dB for some lucky & young fools). This
broadband adjustment is transparent to you most of the time. You notice it
when a loud sound catches you off guard it sometime hurts, but if the sound
is ramped up, it will be tolerable. Its because the coarse volume
adjustment can keep up. Anyway, if you use a loud enough masking source,
the coarse volume adjustment will adjust up. The problem is that what
happens is the other sounds begin to fall into your own ear's noise floor.
You will develop a loss of clarity or eventually have a broadband masking
occur.

A couple of points the these are just from own theorizing.

One is that you may want to try masking with something broadband, but with a
little more structure than pure white noise. Something like filtered
waterfall or engine noise as long as its tolerable. The reasoning is that a
nearly pure tone might be too easy to discern from pure whitenoise. It may
be easier to mask the tone with some broadband noise that has atleast some
structure in it to distract your brain from ferreting out the pure tone.

The other issue is possible bad news. Its referring to the coarse
adjustment that your ear makes with sound. Since you're brain corrects for
the adjustment, I don't know how this will affect the tones coming from
tenitus. You might be fighting a losing battle by trying to increase the
sound level. The course adjustment might just offset the increased sound so
that it is the same relative to the ringing no matter what level of sound
you use. If the ringing was lower, the masking might work, but if the
ringing is very loud as you describe, increasing the volume will actually
just make the ringing seem even louder and the masking may never be enough
to cancel the noise. Hope this isn't the case.

-John