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Old 18th April 2012, 10:24 PM   #4461
SY is offline SY  United States
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Quote:
Originally Posted by janneman View Post

...that ripple - it DOES cause increased levels of harmonics.
Is that actually so? I would think just the opposite, that it's the effect of a complete truncation of upper harmonics.
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Old 18th April 2012, 10:47 PM   #4462
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Originally Posted by dvv View Post
I maintain the we need to have settling times as short as possible and that we need good CURRENT slew rates.
It is obvious: we amplify POWER. It can't consist of VOLTAGE or CURRENT only, it consists of BOTH.
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Old 18th April 2012, 10:48 PM   #4463
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If you simply chop out higher harmonics and leave everything else unchanged then you get symmetrical ripple - equal amounts of pre- and post-ringing. Jan's plots only show post-ringing. However, people do need to remember that ringing does not necessarily mean something has been added to the signal - subtraction can cause ringing too.
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Old 18th April 2012, 11:13 PM   #4464
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Quote:
Originally Posted by SY View Post
Is that actually so? I would think just the opposite, that it's the effect of a complete truncation of upper harmonics.
That's along with my line of thinking, looking at those scope pics - is it real ringing (an actual resonant condition), or is it Gibbs phenomenon? Maybe some of each?

I presume that square wave is 1kHz.
Quote:
Originally Posted by DF96 View Post
If you simply chop out higher harmonics and leave everything else unchanged then you get symmetrical ripple - equal amounts of pre- and post-ringing.
That's with digital filters - the "pre-ringing" building up before the transition is an artifact of sampled filters "looking ahead" at future samples, and can't happen with a traditional analog filter (unless it has a time machine).

Also, all the stated phase shift of this analog filter within its passband no doubt changes the resulting waveshape as well.

In fact, that can be what makes it audible, the resulting waveshape being different, causing a lower or (probably in this case) higher peak that might not be reproduced as accurately as the rest of the waveform. I read something about audible phase with speakers (maybe this thread?), with a 20Hz sawtooth being audibly different when inverted, due to the driver responding differently in the positive direction than the negative direction.
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Jan's plots only show post-ringing. However, people do need to remember that ringing does not necessarily mean something has been added to the signal - subtraction can cause ringing too.
Yes.
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Old 18th April 2012, 11:16 PM   #4465
SY is offline SY  United States
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Dave is right that in a true Gibbs, the ringing is symmetrical. Nonetheless, Jan's scope photo shows the ringing to be at the filter cutoff frequency, so probably not due to higher harmonics since the ringing seems to be a nearly pure damped sine wave.
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Old 18th April 2012, 11:36 PM   #4466
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No matter add you or remove something, wave shape is changed. When you add or remove something periodic, it will be changed periodically.
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Old 19th April 2012, 07:35 AM   #4467
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Originally Posted by janneman View Post
I hear you. But the problem with that is that I (and the others) PREFERRED the signal WITH the ringing; just sounded to me more clear and 'real'...

jan
Not too surprising, if you have been listening to such a source for any longer period of time.

I'd call it "getting used to".

Listen to any type of sound you care to name long enough, and like it or not, you (we) get used to it, at least in part. In a while, it becomes one's reference, not meaning absolute quality, but what we are used to.
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Old 19th April 2012, 07:40 AM   #4468
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Quote:
Originally Posted by Wavebourn View Post
It is obvious: we amplify POWER. It can't consist of VOLTAGE or CURRENT only, it consists of BOTH.
I am glad we agree, W., but this begs the logical question: why is this not recognized widely, instead of promoting only the first half of the whole?

We talk of symmetry, but in real life, we do not adhere to it.

As an example, Siemens Sikorel series of large power capacitors is THE ONE AND ONLY I have ever seen to quote in their specs the current slew rate, beside the voltage slew rate, which is also rarely seen.
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Old 19th April 2012, 08:34 AM   #4469
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Quote:
Originally Posted by dvv View Post
I am glad we agree, W., but this begs the logical question: why is this not recognized widely, instead of promoting only the first half of the whole?

We talk of symmetry, but in real life, we do not adhere to it.

As an example, Siemens Sikorel series of large power capacitors is THE ONE AND ONLY I have ever seen to quote in their specs the current slew rate, beside the voltage slew rate, which is also rarely seen.
Yes but those capacitor current and voltage slew rates are not a property of the cap, they are what the cap can handle without breaking.
Current slew into a cap and the resulting voltage are a function of whatever signal you impress on them (and some secondary effects like the resistance and inductance of cap connection wires and such).

jan
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Old 19th April 2012, 08:37 AM   #4470
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Quote:
Originally Posted by SY View Post
Dave is right that in a true Gibbs, the ringing is symmetrical. Nonetheless, Jan's scope photo shows the ringing to be at the filter cutoff frequency, so probably not due to higher harmonics since the ringing seems to be a nearly pure damped sine wave.
Yes the ringing is at the filter cutoff freq, I missed that. So, whatever the transient period (on the pic indeed a 1kHz square wave), the ringing is always at 15kHz then.
Makes it all the more surprising I heard a difference in 'sharpness'. I mean, I am pretty sure I'm rather deaf at 15kHz...

jan
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