My music sounds brighter

Dirty AC and or unplug all power cords for 5 mins then try it

You removed your big sofa from the room, right?

Drinking any?

Oh wow we just removed our carpet in the dining room prior to a wood floor installation and a clap echoes good.

The room is 50% of the equation in and of sound - in what you hear and interpret.

Any sudden change in humidity ?
https://www.quora.com/How-does-humidity-affect-sound

When we were having the AC replaced this summer the temperature went up to around 80 degrees and the sound was harsh.

Just a guess, but have you added any big power guzzling appliances lately? Has a big power draw come online in your city?

If so, the solution may be an isolation transformer. Trouble is, they tend to growl when working, so they should be sited in a utility room. Plitron makes a good one.

I set up my audio system 1.5 years ago. I've made no changes in the room since.  I have the room temp at 70 degrees and humidity at 50%.  I started noticing the brightness about 2 weeks ago.  And no, I don't drink! 

Just in case, I would clean all the connectors.
This might be the current, I don't know, I have never experienced anything like that.

Are you air conditioned? What was the change in the weather?

We live on the west coast a couple of miles from the beach. August is always a bad month for the HiFi as the listening room gets into the mid 20�°s.

Ear cleaning?

 Yes. AC has been on for a few months now.  This was not an issue last summer.

Acoustics, and the AC power. 

Courtains, rugs, moving furniture? Turning off the gear at night now? 

Also possible, new wifi / radio devices. Alarms, routers, etc. 

oh, and high efficiency lights or dimmers. 

New cable service... what else. Nope, that's it. :) 

Solar activity anyone ??? Nope then we all would posting LOL

Try different source if you can, see what happens. First the cause must be understood then action should follow. Any other approach is BS.

Electromagnetic radiation.
Radio Frequency Interference from Wi Fi devices, laptop, game console or cell phone can effect sound quality especially the top end of a audio signal.
Cell towers seem to be popping up everywhere or a new FM/AM station that is broadcasting their signal at greater strength could also contribute to
RFI changing in a short amount of time.

Lots of suggestions here but what about something like a component in your crossover that is going bad or failed? Is the output of your speakers similar or has one changed?

I'm curious about the DBX. Where is it in the system and how is it wired. Does it need to be on for you to pass a signal thru to speakers? If so, I would look for a forgotten improper setting...or else it could now be ailing. DBX works first by increasing the highs (encoding) and then by decreasing them (decoding). Sudden or intermittent increase in the highs while listening may be a sign of a state of proper encoding but without any (or sufficient) decoding on the back end?

If you need to test, remove the DBX and see if the problem persists.

Look in your Yamaha manual for "Return to factory settings". You may have had some "alien A/C" that screwed with your chip. Start at the beginning. Also, remove the dbx from the system and see how it sounds. Finally, is your wire shielded or unshielded? Unshielded wire (also known as "antennas") will pick-up everything in the air and make things sound bright. Good luck!

I had the same experience I had similar experience. I don’t know your age but I am 71 years old. I developed tinnitus a few years ago and on further research, I discovered that I have developed a condition called hyperacusis, seen often with tinnitus. Everything sounded uncomfortably bright, even my own sibilants. It turns out to be not an uncommon problem. May be you have same or some electro-mechanical problems elaborated by others. By the way, I am a neurologist, not engineer.

I am still puzzled. My set-up sometimes sounds like a big good boombox but never bright, no matter the wall current, weather, whatever.

@giri:  I’m 64 and also have a mild to mid level case of tinnitus. Have you found any treatment that actually works?

@handymann ,
There is some hope, with new research, but I think it is still a few years away:

https://www.mirror.co.uk/science/cure-deafness-discovered-scientists-after-9768342

@handymann There is no particular treatment available but there are some methods to control it, you can check them out at American Tinnitus Association. There is also Hyperacusis Network for more info in case you have hyperacusis. The old treatment of “masking” is helpful selectively, not beneficial in majority of my patients.

@cspiegs,
Interested in update of any progress or elimination of causes to your problem.

@erik_squires,
Spot on with analysis...


@dweller,
Spot on with your analysis also, I have found alien a/c can reach into places past where you can adjust from menu. Try unplugging gear for minute or two and check again...

@giri,I hope you are mistaken and it is not that serious...

Elizabeth

I am all for the ear wax theory. It could also be ear hairs. 

Continually there are changes in our environment - everything from changes in temperature, changes in humidity and air pressure to fluctuations in microwave transmissions - that all have a slight affect on sound and an additional effect on how well we hear it. All of these same things, along with allergy flair-ups, inflammation, blood pressure fluctuations and even minor infections, can have an affect on inner ear and sinus pressure and how we hear at any particular time.
There are some nights I wake up and hear the tic-tock, ticking of both wall clocks in the rooms adjoining my bedroom - almost to the point of wanting to cover my head. Other nights I can barley hear them and sometimes, no mater how hard I listen, not hear them at all.
It could be an unaccounted for change somewhere in the chain of your audio system, but, just as likely, some type of change in your environment or in your self....Jim

How old are the speakers ? If a inner crossover part is going 
Such as a capacitor  that will deduct something from the musical performance. That includes electronics, And does it happen on everything such as cd,records
Even  s new wire or line from your circuit breaker will change 
Sonics. 

I suspect it's the amp. It may need servicing since it is 20 years old.

I just had a checkup and the is nothing wrong with my ears. I don't have the ringing symptoms common with tinnitus and everything else sounds normal. I am more in line to believe there's potentially something wrong with my electronics. However, wouldn't that manifest itself as sounding a duller, not brighter? Except for my turntable and cart, all my electronics are between 20 and 30 years old.

Do you have any Stereophile test CDs? They go thru all frequency ranges. Pay attention to the bass and lower frequencies for deficiencies. Lack of bass makes it sound like your speakers are "top-heavy" when they are actually bass shy.

Not that this solves my mystery but it does improve my listening experience.  As much as I hate employing this, I simply turn down the treble control a few decibels until I'm happy with the sound. It's much better now.

There is a digital high-shelving filter and parametric equalizer (at 12.8 khz) in my Yamaha DSP A1 that I should learn to use (might be beneficial in taming harsher sounding recordings - a subject on equalizers for bad recordings I posted a few months ago) as well. 

If it's bad caps in the amp it could very easily make the sound brighter.

or duller or channel imbalance.

Given the highly integrated circuitry of the DSP-A1, a cap their is an unlikely cause.

Since the OP does not single out a single channel and given it is a multichannel set up, his comment about 'learn to use', a most probable cause is an effects mode change - like from Classical to Jazz - intentional or not.

Thanks to all who actually read the question and answered appropriately.  I will make an ENT appointment and perhaps try some of the home remedies that was in the link ALMARG sent