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5khz audio doesn't HAVE to sound dull. A demonstration

M

Mike Walker

Guest
Limiting analog audio to 5khz in order to enable HD really sucks. It makes the sound worse for current listeners, in order to make it better for future, POTENTIAL listeners. It sucks alright. But MUST it really suck THAT much?

HF audio CAN sound pretty damn dull. A quick measurement of frequency response shows why (duh!) Fortunately our ears aren't laboratory instruments, and are fairly easliy fooled into thinking we're hearing more high frequency content than is actually there.

Others here (hi Tom!) have suggested that the way to restore "balance" to the sound is to rolloff bass response. In otherwords, compensate for narrowband audio BY MAKING IT NARROWER! This may have made SOME sense 40 years ago when available tools were much cruder, but today it makes absolutely none. Again, the ear can be fooled into believing there's more hf content than there actually is...through a process Aphex has called "Aural Excitation" for three decades or so. Now there are both hardware boxes (from Aphex and others) and software plugins (I used a freeware one called the RGC Audio HF Stimulator for this demonstration) that allow us to "add" harmonics. Let's not call it what it is...HARMONIC DISTORTION. After all, it's "even order" which sounds very musical to our ears. What I did was crank up "drive" and "mix" to 100 percent, generating a helluva lot of extra harmonics in the little over an octave between 2 and 5khz...restoring the illusion of ample "highs'. By the way, NOTHING has been done to the lows...low frequency response is equally extended on all three files I created for the demo.

Below are the three files. All are 320kbps mp3 files, to keep space down, while still having good enough quality to illustrate my point. One is full bandwidth 20khz from the cd of "Year of the Cat"...the song "On The Border" by Al Stewart. It's DRENCHED in highs, but will a very full bass line as well...which is why I selected it. On the second file I have simply chopped off everything above 5khz (using the bandwidth control in Adobe Audition's mp3 encoder). On the third, I used the harmonics generator program as discussed above, added a hard limiter at -.3db to keep "splat" to a minimum from all the extra hf content, and again chopped off everything above 5khz when saving the file. You may be surprised that the 'brightest" sounding file is the one with the "hf stimulation" (harmonics generator) with bandwidth limited to 5khz. So much for having to roll off bass in order to make things sound "balanced".

On the Border 20khz bandwidth, no processing http://www.theproductionroom.net/border20k.mp3

On the Border 5khz bandwidth, no processing
http://www.theproductionroom.net/border5k.mp3

On the Border 5khz WITH ADDED HARMONICS and hard limiting to prevent overload
http://www.theproductionroom.net/border5kexcite.mp3

"Aural Exciters" anyone? If we're REALLY going to limit highs to 5khz, maybe it's time to buy stock in Aphex!
 
:-\ Well, it is less muddy, but reminds me of listening to the midrange driver on a three-way speaker.

You are correct that creatively applied (even)harmonic distortion can sound musical and brighten muddy audio.
It is a "desirable" distortion as it mimics natural reasonance in physical objects and spaces.

I might think boosting the highs just between 4 and 5 Khz would be less...squawky.

When cutting off upper frequencies, a sharp peak at the upper limiting frequency will definitely make the most of whatever audio is presented, though this is "frequency distortion".

I appreciate that people have different preferences for audio.
The Aphex aural exciters almost always make sound full and rich.
I sure wish the Ramones had recorded with one.
 
You're right...a rise in response just before the nosedive also helps fool the ear into thinking it's hearing something that actually isn't there.

As I said, 5khz audio SUCKS. It's just a question of "can we live with the suckage, and can we do anything to minimize it's effects?"
 
Mike Walker said:
Limiting analog audio to 5khz in order to enable HD really sucks. It makes the sound worse for current listeners, in order to make it better for future, POTENTIAL listeners. It sucks alright. But MUST it really suck THAT much?
Click to expand...

As mentioned elsewhere, Bob Orban studied a broad assortment of consumer receivers and found that the AM band was down an average of 10 db at 4.1 kHz. It does not matter what is transmitted if the majority of receivers suck.
 
DavidEduardo said:
Mike Walker said:
Limiting analog audio to 5khz in order to enable HD really sucks. It makes the sound worse for current listeners, in order to make it better for future, POTENTIAL listeners. It sucks alright. But MUST it really suck THAT much?
Click to expand...

As mentioned elsewhere, Bob Orban studied a broad assortment of consumer receivers and found that the AM band was down an average of 10 db at 4.1 kHz. It does not matter what is transmitted if the majority of receivers suck.
Click to expand...

I can't beleive you said it does not matter what is transmitted if the majority of receivers suck.

By this logic, fine food establishments should close their doors because most people don't recognize
or appreciate the value of high quality.

If quality does not matter, why use anything better than POTS for an STL?

I seriously doubt Mr. Orban is looking out for the best interests of the AM broadcaster in making such statements.
Such a statement clearly is leading up to justification for IBOC, where "no one will hear the sidebands anyway because the radios are too muddy. Sure, if you want find bad examples, they're out there, but really, MOST radios down 10 db at 4 kc?
That's some pretty selective shopping and radios.
Oh, and I'm sure he was using "center tuning" to prevent any possible situation where the same radios (if analog tuned)
would be down 10 db at 8kc.

I'm sure he considers the Delco mufflemasters to be a fine AM car radio.
The last good sounding AM Delco was back in the 80's.
The crop since then have such limited audio as to make the treble control worthless for AM.
Why did Ford and Chrysler decide to keep high frequency response on AM?

Why didn't ibiquity choose a Ford or Chrysler radio for their sample set?
 
Besides DaveEduardo, you neglected to point out that, in the days before the NRSC response curve and the 9khz brickwall filter, Orban was able to equalize flat response to 8khz or higher from "average" am radios. As the Optimod manual said in those days "this requires A LOT of pre-emphasis, but CAN BE DONE" (very close to an exact quote from a 1980s Optimod AM manual). ;)
 
Mike Walker said:
"Aural Exciters" anyone? If we're REALLY going to limit highs to 5khz, maybe it's time to buy stock in Aphex!
Click to expand...

I'm surprised that aural exciters aren’t common on many radios. BBE sells their chip and licensing at very reasonable cost (pennies). My TV has BBE in it, and it really does help make those cheap speakers sound better. Of course Aphex was the originator of the idea, even though it was an accident. They make some very good stuff.

Even the poorest radio station ought to be able to afford Behringer's exciter. It usually sells for about $99 and it actually works pretty well. It even has balanced XLR inputs and outputs.
 
I have been reading the "back and forth" debate (at times you could call it a "catfight") on HD Radio for
several weeks. Based on what I have heard (and yes, I have "tried out" HD Radio), I ain't impressed with it.
I am just going to "vote" with my wallet and not buy into it.

Lack of decent content and programs seems to be radio's biggest problem, not audio/sound quality.

Tim
 
Patlabor said:
I have been reading the "back and forth" debate (at times you could call it a "catfight") on HD Radio for
several weeks. Based on what I have heard (and yes, I have "tried out" HD Radio), I ain't impressed with it.
I am just going to "vote" with my wallet and not buy into it.

Lack of decent content and programs seems to be radio's biggest problem, not audio/sound quality.

Tim
Click to expand...

Tim, thanks for you your input. Agreed that programming is not necessarily the best and is the largest driver of listeners. I believe the idea behind HD radio is bringing the last analog medium into the digital age. Everything else (internet, cellular phones, television, ipod, etc) is digital these days and radio needs to join in the digital transmission format. The biggest issue here is whether or not the current transmission method either "works" or is the best method of transmission. I encourage you to draw your own conclusions (which it seems like you already have based on your post.) Thanks for your rational contribution.

Steven
 
Amen, Steven. You considered the options, studied the technology, tried HD, and decided it wasn't of value to you. So you respectfully told us how you felt. Who could take issue that? And with no name calling, no conspiricy theories, and no BS. I wonder why so many who are in your camp (the "thanks, but no thanks to HD" camp) feel the need to be so rude. Notice how we (in the pro-HD camp) responded when a person with an anti-HD point of view expressed an opinion in a civil manner? We (the pro-HD guys) considered his point of view, and thanked him for his input. Wouldn't you guys on the other side like to actually DISCUSS this? Because honestly I mostly don't even read your posts, and never follow your links. Nobody can bully me into anything. But discuss radionally, and you might just change my mind. You'll certainly get my attention, as RF did with his demonstrations.

Let's all actually CONTRIBUTE. Hear something amiss? DOCUMENT IT...record it for us. If you feel measurements reveal more, MEASURE IT and show us your data (pics of scope traces/screen shots/etc). LET'S ALL CONTRIBUTE...honestly, and respectfully.
 
Mike Walker said:
Limiting analog audio to 5khz in order to enable HD really sucks. It makes the sound worse for current listeners, in order to make it better for future, POTENTIAL listeners. It sucks alright. But MUST it really suck THAT much?

HF audio CAN sound pretty damn dull. A quick measurement of frequency response shows why (duh!) Fortunately our ears aren't laboratory instruments, and are fairly easliy fooled into thinking we're hearing more high frequency content than is actually there.

Others here (hi Tom!) have suggested that the way to restore "balance" to the sound is to rolloff bass response. In otherwords, compensate for narrowband audio BY MAKING IT NARROWER! This may have made SOME sense 40 years ago when available tools were much cruder, but today it makes absolutely none. Again, the ear can be fooled into believing there's more hf content than there actually is...through a process Aphex has called "Aural Excitation" for three decades or so. Now there are both hardware boxes (from Aphex and others) and software plugins (I used a freeware one called the RGC Audio HF Stimulator for this demonstration) that allow us to "add" harmonics. Let's not call it what it is...HARMONIC DISTORTION. After all, it's "even order" which sounds very musical to our ears. What I did was crank up "drive" and "mix" to 100 percent, generating a helluva lot of extra harmonics in the little over an octave between 2 and 5khz...restoring the illusion of ample "highs'. By the way, NOTHING has been done to the lows...low frequency response is equally extended on all three files I created for the demo.

Below are the three files. All are 320kbps mp3 files, to keep space down, while still having good enough quality to illustrate my point. One is full bandwidth 20khz from the cd of "Year of the Cat"...the song "On The Border" by Al Stewart. It's DRENCHED in highs, but will a very full bass line as well...which is why I selected it. On the second file I have simply chopped off everything above 5khz (using the bandwidth control in Adobe Audition's mp3 encoder). On the third, I used the harmonics generator program as discussed above, added a hard limiter at -.3db to keep "splat" to a minimum from all the extra hf content, and again chopped off everything above 5khz when saving the file. You may be surprised that the 'brightest" sounding file is the one with the "hf stimulation" (harmonics generator) with bandwidth limited to 5khz. So much for having to roll off bass in order to make things sound "balanced".

On the Border 20khz bandwidth, no processing http://www.theproductionroom.net/border20k.mp3

On the Border 5khz bandwidth, no processing
http://www.theproductionroom.net/border5k.mp3

On the Border 5khz WITH ADDED HARMONICS and hard limiting to prevent overload
http://www.theproductionroom.net/border5kexcite.mp3

"Aural Exciters" anyone? If we're REALLY going to limit highs to 5khz, maybe it's time to buy stock in Aphex!
Click to expand...

So, broadcasters should transmit the lowest fidelity sound they can so that everyone will have buy Aphex Exciters to add to their radios in order to get half decent fidelity?

The whole reason for high fidelity is to not have to fool the ear into thinking it is hearing something that it is not. Fooling the ear results in listener fatigue, and tune outs.

Following your logic, high fidelity, especially destructive HD Radio, is not only unnecessary, it is undesireable.

If everyone can or does add these Aphex Exciters to their radios, and they work so perfectly then why bother with problematic HD Radio?

Are you saying high fidelity is a waste?

Should analog FM and HD radio also be limited to 5khz since any more fidelity is unnecessary and undesireable?

Certainly HD radio is.
 
I never said it was idea. I prefaced my comments with "5khz audio sucks". The demonstration was to prove that it can be made to suck LESS. The ear perceives "brightness" at lower frequencies than most people think. Those were my only points.

I'm a HUGE fan of wideband AM! I grew up listening to AM in a day when no tricks were needed to make it sound bright and clean...it already sounded bright and clean! HD may eventually saddle us with lemons (5khz audio) All I intended to do was suggest a recipe for lemonade ;)
 
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