Home Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

[ Follow Ups ] Thread: [ Display  All  Email ] [ Propeller Head Plaza ]
[ Alert Moderator ]

You can’t compare the end result.

I’m fully aware of that control theory and audio amplifier design share characteristics and I didn't mean to imply that audio amplifier feedback networks have "ears and brains", I was just referring to the end-user. (And a P-regulator is truly nothing else than a feedback amplifier.) The difference lies in that in control theory it doesn’t matter if the error consists of 2:nd, 3:rd… 7:th or 20:th order harmonics, as long as the total error is small enough. Like when you measure THD without specifying the harmonics… ;-)

“One has to interface with the physical world using transducers, servo motors, and sensors. The other is purely electronic. But that's where the difference ends”

“The other is purely electronic.”????????

Don’t you listen to music with your ears? If audio where purely electronic our brains would be connected directly to the amplifiers via cable, without the need of loudspeakers and our ears. Actually this is an intriguing and interesting idea. But until this comes true we need our EAR-BRAIN system to hear things.

Our ear-brain system is constantly listening for changes in the sound information and tries to interpret that. Take noise as an example, if the noise is constant in its character we don’t hear it as easily opposed to when its constantly changing. A friend of mine gave me a good example of this; When you are driving a car you don’t recognise the background-noise from the tyres against the tarmac after a while. BUT if the asphalt surface changes you immediately recognise the CHANGE and start hearing the noise again.

This is probably one of the reasons to why vinyl works despite the S/N-ratio of around 70 - 75 dB at it’s best, the noise character is constant. And as Fielder pointed out in one of his papers; we have the ability to hear information 10 to 15 dB BELOW the background-noise. That would make a "true" S/N-ratio of up to 90 dB because I believe that the low-level information is there in the noise and that we can hear it.

Our ear-brain system is sensitive to high order distortion as pointed out by Shorter and Crowhurst already in the 50’s but the root cause might not be that high order distortion products are dissonant, but instead the enormous number of IM-products with several simultaneous tones.

In music the number of simultaneous tones can be very high when considering all the natural harmonics of musical instruments, just look at a guitarist playing one chord; 6 tones and I don’t know how many harmonics but just say it ads up to 20 something (Probably more).

If we look at a system with only 2:nd order distortion and 20 simultaneous input tones we get 380 IM-products and with a total distortion level that is almost 9 times higher compared to what it would be with a single tone.

If we look at a system with only 3:rd order distortion and 20 simultaneous input tones we get 5320 IM-products and with a total distortion level that is 95 times higher compared to what it would be with a single tone.

If we look at a system with only 4:th order distortion and 20 simultaneous input tones we get 53 960 IM-products and with a total distortion level that is 123 times higher compared to what it would be with a single tone.

If we look at a system with only 5:th order distortion and 20 simultaneous input tones we get 437 560 IM-products and with a total distortion level that is 93 times higher compared to what it would be with a single tone.

And this just gets worse with higher harmonics and our systems don’t just have one order of distortion but 2:nd, 3:rd, 4:th and so on. This means that higher order harmonics create a constantly changing “noise-floor” witch is modulated with the input signal. This may explain the metallic and grainy sound we encountered with systems with high order distortion.

This implies that harmonic distortion with constantly changing character is detected by our ear-brain system, while listening to music, even if it’s at very low levels. And because our brain is trying to interpret this “information” witch isn’t relevant information listening-fatigue will occur.

And that brings me back to why I don’t think that you compare control theory with audio amplifier design. In control theory the order of harmonics don’t matter, only that the error is small enough matter. And in control systems you often only have to cope with only one input signal. That’s one tone. ;-)

But to our ear-brain system the order of harmonics and the number of IM-products matter and we obviously have the ability to hear information down below the noise-floor of our system and since changes are interpreted as information………… Hmmmm! Well I think I made my point clear now and won’t go on. I only want to wish a happy new year to all of you.


Enjoy Creating / Mad Man Harju

This post is made possible by the generous support of people like you and our sponsors:
  Parts Connexion  

Follow Ups Full Thread
Follow Ups
You can not post to an archived thread.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]