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Old 26th October 2012, 02:50 PM   #11
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Expired patent:
Patent US4318053 - Amplifier system with automatic distortion control - Google Patents
"charges a capacitor proportionate to the percent clipping of the output of the amplifier"
I'm not sure what you call that circuit, but in awaiting a cap to charge, the device will sound just like a compressor/limiter.

Here's a television compressor/limiter: http://www.amazon.com/Audiovox-Terk-...ews/B00008VWOJ
That one is very aggressive so there's sometimes a pop or pulse when it engages. To decrease the disturbances, one would set the compressor/limiter to be less effective and then the difference between modified versus unmodified signal is decreased.

P.S.
I believe that a soft clipper is faster than either of those, no pop, no pulsing, and that a soft clipper has a treble effect that sounds somewhat like tube/valve amp clipping. So, that's different, isn't it?
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Last edited by danielwritesbac; 26th October 2012 at 03:08 PM.
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Old 26th October 2012, 04:37 PM   #12
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I dont see how a (perfect) clipper (hard or soft) can add noise to the signal. Noise is a non harmonic signal, random. A clipping add distortion. A soft clipper just reduce upper harmonics from it. It just smooth the corners of a square wave.
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Old 26th October 2012, 04:53 PM   #13
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Quote:
Originally Posted by danielwritesbac View Post
I believe that a soft clipper is faster
There is no question of speed, here.
A compressor or limiter can be faster than anything else, because it can even reduce level before the peak happens. Using DSPs and delays.
A compressor change the average gain of an amplifier, it reduce the volume, like you could do it with a volume control. Its action is supposed to be linear from 0 to max of a signal, reducing the overall gain factor.. It does not clip any signal. You have access to the detection speed, the speed of recovery, the level threshold and the compression ratio. The limiter is just a compressor with a ratio > 10/1.

A clip is just an electric limitation of the max voltage of an electric signal signal. Due to rail voltage limitations, in an amp. A soft one is one witch has a transition curve near this point.
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Old 26th October 2012, 04:54 PM   #14
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Quote:
Originally Posted by Esperado View Post
I dont see how a (perfect) clipper (hard or soft) can add noise to the signal. Noise is a non harmonic signal, random. A clipping add distortion. A soft clipper just reduce upper harmonics from it. jut just smooth the corners of a square wave.
Please pretend that I said distortion.
Apparently, I was using the word noise in the most common way according to Wikipedia: "In relation to sound, noise is not necessarily random. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. "

The article goes on to explain that it has different meaning to engineers, specifically random or hiss: Noise - Wikipedia, the free encyclopedia
I did not know that engineers used this word differently than common usage.
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Old 26th October 2012, 05:08 PM   #15
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The compression ratio of a compressor determine the non linear gain factor of the action. You can set-it, for example, for each 6db increase of a signal will produce a 3db gain at the output. It has to be clear: it is the gain of the amp during all the duration of this signal (at least one sinusoid).

You can set delays for different feels. With a fast attack and a long recovery, you can reduce the volume of any loud signals.Volume decrease at the attack and stay at a lower level. After the average high level material of the signal has stopped, the gain will slowly increase.
On the contrary, using slow attack and fast recovery, you can let the peaks, and reduce volume after. Adding attack to a bass that way is a common practice in mixing processes.
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Last edited by Esperado; 26th October 2012 at 05:17 PM.
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Old 26th October 2012, 05:15 PM   #16
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Used in audio, noise is an added random signal, not in correlation with it.
Can be produced by different factors, like random movements of atoms in transistors or resistances due to thermal effects, random repartition of the elementary magnets on an magnetic tape, random roughness of the vinyl groove.
Distortion is a deformation of the signal itself.
When no signal, noise can continue, while no distortion can occur.
In certain circumstances, noise can be modulated by the signal, but, again, no harmonic correlation with the signal itself.
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Last edited by Esperado; 26th October 2012 at 05:19 PM.
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Old 26th October 2012, 05:49 PM   #17
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Quote:
Originally Posted by Esperado View Post
There is no question of speed, here.
A compressor or limiter can be faster than anything else, because it can even reduce level before the peak happens. Using DSPs and delays.
A compressor change the average gain of an amplifier, it reduce the volume, like you could do it with a volume control. Its action is supposed to be linear from 0 to max of a signal, reducing the overall gain factor.. It does not clip any signal. You have access to the detection speed, the speed of recovery, the level threshold and the compression ratio. The limiter is just a compressor with a ratio > 10/1.
Very true! More modern compressors do have DSP's that can match the timing up so there's no audible pulsing.

By your description, what you're wanting is a DSP based Line Level PA/Prosound type compressor. With those, its not necessary to clip anything in order to activate a detector. Instead, you program the level and the DSP regulates the output of this line level device. In that line level scheme, you don't have to reduce the output power of your amplifier by early engagement of compressor.
Quote:
Originally Posted by Esperado View Post
A clip is just an electric limitation of the max voltage of an electric signal signal. Due to rail voltage limitations, in an amp. A soft one is one witch has a transition curve near this point.
That's a really good definition. Thanks!!
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Old 26th October 2012, 05:55 PM   #18
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About the Pipipedia " "In relation to sound, noise is not necessarily random. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. " i suppose their refer to the content of the audio material, not the quality of its reproduction.
It is obvious that any unwanted background behind a dialog, by example, like car ambiance, is called noise. Not at all the same thing, as a good amp with -110db of signal/noise ratio will reproduce perfectly this noisy recording.
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Old 26th October 2012, 06:09 PM   #19
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About what i'm looking for, is a clipper able to clip a signal in a identical way that following amp can do.
Without adding noise or distortion in the non clipped signal.
The reason is that i use a comparator in a protection circuit, between the input and the output signal, to detect any DC, oscillation, cutoff, even noise or unwanted distortion added by the amp, that would reveal its dysfunction.

The problem is that amp clipping introduce such a difference between input and output, while no dysfunction of it.
So the idea was to clip the input signal, just before the max peak level of the amp. I will compare the two, clipped input signal with amplified not clipped signal of it at the output, whatever the input level.
Of course, because it is supposed to be a protection, even in high end amps, it is requisite that this clipping circuit will not deteriorate the quality of the signal in any way.
Such a perfect circuit will just remove little percent of the peak power capability of the amp.
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Last edited by Esperado; 26th October 2012 at 06:14 PM.
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Old 27th October 2012, 01:47 AM   #20
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For the moment, i'm on this simple idea: + 2 adjustable zener Diodes.
The interest is that it has no action before the threshold, because just a resistance in the signal path.
http://www.diyaudio.com/forums/attac...it-limiter.gif
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