# Comparing original sine with Clipped sine



## fertigaudio (Jul 18, 2010)

I am reading a text book about amplifier design and was thinking (after searching for a while) why not compare the input signal to the output signal minus the gain of course and adjust the gain potentiometer circuit automatically thus getting rid of any clipping that would ensue from the lobbed off sine wave.

if the output sine starts to clip then the circuit would adjust gain on the front end of the amplifier to compress or reduce that particular sine in real time. 

if at levels lower than the the clip then the amp reference to all particular frequencies would gain to return to normal at un-clipped levels.

Amps with clip light circuits already compare signals why not take it a step furthur and do this for car amps. There is a fancy circuit like this in my Peavey Pro audio equipment and I could clip the heck out of it and my 18's would not distort... 

RADIO EDIT: Found this. DDT circuit is Peaveys own design.
DDT senses clipping (or current limiting) and reduces the gain to prevent audible distortion. In mixers we provide metering and clip/OL indicators. Recently, competitors' advertising has made a big deal about "headroom." One would be led to believe from the frequency of such statements that they somehow have more headroom than others—not so. Most contemporary mixer designs share similar limitations, namely, the power-supply voltages. The voltages are further defined by the integrated-circuit technology. Most general-purpose ICs are manufactured with a 36V process; this limits the power supply to +/-18V max. The more conservative approach, +/-15V rails, costs a mere 1.5 dB of headroom for increased reliability. There will be small to nonexistent headroom differences between competing mixers.

Shouldn't this become common place in car audio, some might call it overbuilding... CEA already has the 2006 standards add an addendum to it and state these performance requirements or add to the EIA-RS-490 or EIA 517B...


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## lycan (Dec 20, 2009)

It's been done for decades : McIntosh PowerGuard.

Even their car amps have it


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## fertigaudio (Jul 18, 2010)

lycan said:


> It's been done for decades : McIntosh PowerGuard.
> 
> Even their car amps have it


haha, maybe i have been expecting too much out of cheap amps then, :blush:


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## MarkZ (Dec 5, 2005)

Not a bad idea. You could always buy a processor with a limiter feature and calibrate it yourself and it would do what you describe. This is easy for carPC folks, obviously. I seem to remember the Behringer DCX2496 had a limiter too, so there's another possibility.


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## cubdenno (Nov 10, 2007)

lycan said:


> It's been done for decades : McIntosh PowerGuard.
> 
> Even their car amps have it


You're still here!!! I have been missing your high mathematic content posts!!!


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## t3sn4f2 (Jan 3, 2007)

lycan said:


> It's been done for decades : McIntosh PowerGuard.
> 
> Even their car amps have it


Pioneer PRS amps have something similar as well.


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## usacimember (Dec 24, 2009)

lycan said:


> It's been done for decades : McIntosh PowerGuard.
> 
> Even their car amps have it


2nd that


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## sqshoestring (Jun 19, 2007)

I agree, but I don't have a Mac amp lol. Things like this make me wonder why some products are so stuck in the past. HT/pro has had DSP and complex EQ for decades yet the P99 is super special when you could do all this on a chip long ago, why is it so hard, wtf are these companies doing did they finally hire an engineer with a little ambition while the rest slept and played porn on the internet the last decade? Only government workers should be allowed to do that, I thought that was the rule maybe I was wrong lol. Its like the cell phone companies that give you a phone for free or cheap and when you read on the net it says that phone can do a thousand things yet for some reason all that technology has been disabled on your phone....I'd move to Russia if I wanted to live there. I can buy a birthday card that sings me a song for a few bucks but make me a better amp in China, no can't do it! We iz too retardicapped to do it....is the feeling I get. I can buy a CD player or radio for $30 with a remote control, yet they want hundreds to put a simpler remote on a snow plow. Yeah I'll stop rambling now.


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## envisionelec (Dec 14, 2005)

sqshoestring said:


> wtf are these companies doing...
> We iz too retardicapped to do it....is the feeling I get.



No. Freaking. Kidding.


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## envisionelec (Dec 14, 2005)

fertigaudio said:


> I am reading a text book about amplifier design and was thinking (after searching for a while) why not compare the input signal to the output signal minus the gain of course and adjust the gain potentiometer circuit automatically thus getting rid of any clipping that would ensue from the lobbed off sine wave.
> 
> if the output sine starts to clip then the circuit would adjust gain on the front end of the amplifier to compress or reduce that particular sine in real time.
> 
> ...


Well, that quote doesn't talk about what DDT actually does. It's a clipping limiting circuit, meaning it turns the gain down according to the state of the amplifier. It's compression. Yes, every good car amp should have it - it would save a lot o' woofers. But, car audio amp companies *MUST SELL WOOFERS*, so they don't put it in their amps. Greed.


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## MidnightG35X (Feb 5, 2009)

To make a "clip" indicator, all you need is a simple voltage comparator. You KNOW the amp will clip when it gets very close or hits the power supply rail. Just set the reference for the comparator to that voltage, and whenever the comparator output goes high, you're clipping  You can do what you want with the comparator output (light, reduce gain, etc). Granted this is only for voltage clipping, not an overcurrent condition (which isn't really clipping anyway).


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## MarkZ (Dec 5, 2005)

Also need a holdup circuit, so that the light stays on when clipping is detected. Otherwise, it might be too fast to see it. Unless you only want to detect severe clipping.


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## sqshoestring (Jun 19, 2007)

I have an Infinity amp with the clipping light on it, I was going to look at the circuit and see what they had in there. I figured it was something like a comparator.

Has to be 3v for an LED too.


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## envisionelec (Dec 14, 2005)

MidnightG35X said:


> To make a "clip" indicator, all you need is a simple voltage comparator. You KNOW the amp will clip when it gets very close or hits the power supply rail. Just set the reference for the comparator to that voltage, and whenever the comparator output goes high, you're clipping  You can do what you want with the comparator output (light, reduce gain, etc). Granted this is only for voltage clipping, not an overcurrent condition (which isn't really clipping anyway).


That's not entirely true. A simple voltage comparator will tell you when you're near rail voltage, but doesn't tell you if you're clipping. You need to be able to compare the input signal with the constructed output and compare. But that's not all. You'll need rectification, slope compensation and peak-hold circuits to get that accurate representation.


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## MidnightG35X (Feb 5, 2009)

envisionelec said:


> That's not entirely true. A simple voltage comparator will tell you when you're near rail voltage, but doesn't tell you if you're clipping. You need to be able to compare the input signal with the constructed output and compare. But that's not all. You'll need rectification, slope compensation and peak-hold circuits to get that accurate representation.


Maybe its because its late at night now, but what would cause clipping besides being close the rail voltage? I guess I'm talking about straight clipping, not distortion in general. There are plenty of exotic ways to deal with distortion besides a simple voltage comparator


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## t3sn4f2 (Jan 3, 2007)

MidnightG35X said:


> Maybe its because its late at night now, but what would cause clipping besides being close the rail voltage? I guess I'm talking about straight clipping, not distortion in general. There are plenty of exotic ways to deal with distortion besides a simple voltage comparator


The power supply not being able to provide the current for a difficult load versus an simpler one.


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## MarkZ (Dec 5, 2005)

MidnightG35X said:


> Maybe its because its late at night now, but what would cause clipping besides being close the rail voltage? I guess I'm talking about straight clipping, not distortion in general. There are plenty of exotic ways to deal with distortion besides a simple voltage comparator


I think it's splitting hairs a bit, but being near the rail voltage (by how much?) could be perfectly fine as long as your peaks aren't trying to exceed it.

It all depends on what you're trying to do. Your solution would be fine IF you only want to detect severe clipping. If, on the other hand, you want to detect any instance of clipping, then you need to compare to the input signal and trigger the light to stay on for a long enough time for the eye to be able to detect it.


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## envisionelec (Dec 14, 2005)

MidnightG35X said:


> Maybe its because its late at night now, but what would cause clipping besides being close the rail voltage? I guess I'm talking about straight clipping, not distortion in general. There are plenty of exotic ways to deal with distortion besides a simple voltage comparator


The concept is correct - looking at output getting close to rail voltages. But you can't just hook a comparator to the output and call it done. You'll be seeing the light flash, but it won't be accurate if you want to indicate other types of distortion than straight clipping.

The slope compensation takes into account the rail voltages as well as program content. Without this, the threshold is constantly moving.


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## MidnightG35X (Feb 5, 2009)

Yea, I knew it wouldn't be accurate for other types of distortion, but I saw a clipping indicator, so that's what I proposed. I agree you'd need some holdup on the output of the comparator to actually see light clipping, but in my mind the concept is sound 

If we want to get real fancy, can we do some digital pre-distortion?


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## envisionelec (Dec 14, 2005)

MidnightG35X said:


> Yea, I knew it wouldn't be accurate for other types of distortion, but I saw a clipping indicator, so that's what I proposed. I agree you'd need some holdup on the output of the comparator to actually see light clipping, but in my mind the concept is sound
> 
> If we want to get real fancy, can we do some digital pre-distortion?


Yes, just be sure to rectify the signal first to monitor both rails...


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