Time advanced error feedback correction - Page 3

Sch3mat1c · 25th March 2004, 08:00 PM

Hmm...may be true, may not be. We'll have to wait and see!

Since the rectified HF signal is essentially AVC, you could tap into it and bias it for electronic volume control, couple in some audio (plus a shaping circuit for log/exp. AVC response) for compression or expansion, etc. Hmmm...

Tim

smoking-amp · 25th March 2004, 08:17 PM

Chapter 2.5 .1.2.6.1.4.2.1...

Thinking about this a little more, I think one could look at the gain control feedback loop (in the gain multiplier designs, including the dither design) as a simple classical control system that is trying to maintain a setpoint versus external interfering influence (the input signal excercising different operating points with slightly different gains). So what is needed is critical damping in the gain control loop to minimize the residual effects of control level changes. Also, the correct gain to maintain accurate setpoint.

So distortion correction effects would still have some trailing influence somewhat like in conventional NFB loops, but I think this would be a very small effect for a well designed amplifier due to the small level of change of gain except near saturation. So the (multiplier) control level is hardly changing for large signal variations. Also, the effect of a critically damped bounce in the control level may simply allow some uncorrected distortion thru rather than generating new higher harmonics, but would need to simulate or test this. Generally though, for a control system that is fast compared to the stimulus signal, the effect of changing input is to just generate a small slew related lag error in the control level, and this should not be a problem. I think! (Darn, where's that control system book from 30 years ago?)

Don

Prune · 12th November 2004, 10:02 AM

I am curious, what is the problem with simply taking into account the whole signal path (DAC->Speaker&RoomReflections) distortion and digitally predistorting the signal?

Sch3mat1c · 12th November 2004, 02:54 PM

Nothing, but it doesn't adapt to *anything*. It'll sound good with your head positioned in exactly the correct spot.

Complicated to get a good measurement anyway.

Tim

Prune · 12th November 2004, 11:32 PM

So? Just use head-tracking tehcnology.

Sch3mat1c · 13th November 2004, 03:24 AM

Y'mean headphones? :P

25th March 2004, 08:00 PM	#21
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Hmm...may be true, may not be. We'll have to wait and see! Since the rectified HF signal is essentially AVC, you could tap into it and bias it for electronic volume control, couple in some audio (plus a shaping circuit for log/exp. AVC response) for compression or expansion, etc. Hmmm... Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

25th March 2004, 08:17 PM	#22
smoking-amp diyAudio Member Join Date: Dec 2001 Location: Hickory, NC	different perspective Chapter 2.5 .1.2.6.1.4.2.1... Thinking about this a little more, I think one could look at the gain control feedback loop (in the gain multiplier designs, including the dither design) as a simple classical control system that is trying to maintain a setpoint versus external interfering influence (the input signal excercising different operating points with slightly different gains). So what is needed is critical damping in the gain control loop to minimize the residual effects of control level changes. Also, the correct gain to maintain accurate setpoint. So distortion correction effects would still have some trailing influence somewhat like in conventional NFB loops, but I think this would be a very small effect for a well designed amplifier due to the small level of change of gain except near saturation. So the (multiplier) control level is hardly changing for large signal variations. Also, the effect of a critically damped bounce in the control level may simply allow some uncorrected distortion thru rather than generating new higher harmonics, but would need to simulate or test this. Generally though, for a control system that is fast compared to the stimulus signal, the effect of changing input is to just generate a small slew related lag error in the control level, and this should not be a problem. I think! (Darn, where's that control system book from 30 years ago?) Don __________________ Ohms Law V = I R

12th November 2004, 02:54 PM	#24
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Nothing, but it doesn't adapt to anything. It'll sound good with your head positioned in exactly the correct spot. Complicated to get a good measurement anyway. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

13th November 2004, 03:24 AM	#26
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Y'mean headphones? :P __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

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12th November 2004, 10:02 AM	#23
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	I am curious, what is the problem with simply taking into account the whole signal path (DAC->Speaker&RoomReflections) distortion and digitally predistorting the signal?

12th November 2004, 11:32 PM	#25
Prune Account Disabled Join Date: Mar 2003 Location: Vancouver	So? Just use head-tracking tehcnology.

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