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Old 7th August 2006, 03:11 PM   #11
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I don`t think I understand last post...
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Old 7th August 2006, 04:54 PM   #12
sreten is offline sreten  United Kingdom
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Hi,

THD is simply the linear sum of the harmonics + noise compared to the signal.

So one amplifier could have 5% THD consisting mainly of 2nd harmonic.

Another could have 5% spread evenly across the harmonics up to 20K.

The second will sound very much worse than the first.

The formula I gave is a way of weighting harmonics to more accurately
reflect their impairment of sound quality. It shows why a valve amplifier
with 3% distortion could sound nicer than a transistor amplifier with 0.5%.

Weighting is not popular as it always increases the quoted distortion figure.

Weighting is popular when it improves the quoted figures,
for example A-weighted rumble figures for turntables.

/sreten.
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Old 8th August 2006, 07:39 PM   #13
Steven is offline Steven  Netherlands
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Default How to calculate harmonic distortion

Just to make the calculations a bit more clear:
In the shown graph the fundamental has a level of 30dB, the 2nd harmonic is -40dB, 3rd also -40dB, 4th is -56dB, 5th also -56dB, etc.
If we normalise the fundamental to 0dB, then the 2nd harmonic is 70dB below the fundamental, so at -70dB, 3rd at -70dB, 4th at -86dB, 5th at -86dB, 6th ~ 9th at -100dB.
For calculation of the THD it is easy to go back to real values instead of dBs. The fundamental is 0dB = 1, the 2nd harmonic is -70dB = 10^(-70/20) = 3.16E-4, 3rd also 3.16E-4, 4th is -86dB = 10^(-86/20) = 5.01E-5, 5th also, 6th ~9th harmonic is -100dB = 1E-5.

Total harmonic distortion (THD) is the square root taken from the sum of the harmonics squared, divided by the fundamental.
THD = SQRT((3.16E-4)^2) + (3.16E-4)^2 + (5.01E-5)^2 + (5.01E-5)^2 + (1E-5)^2 + ...)/1 = 4.53E-4 = 0.045%

Weighted harmonic distortion (WTHD) takes into account that higher harmonics are more annoying than lower oder harmonics. Shorter proposed in 1950 the n^2/4 rule, with n is the number of the harmonic. So 2nd harmonic is multiplied by 1, the 3rd by 9/4, et cetera. After weighing of the harmonics, the WTHD is calculated in the same manner as the THD. In the above case the WTHD is 9.13E-4 = 0.091%. This is not much worse than the unweighted THD because higher harmonics are very low in this example. If e.g. the 9th ahrmonic would have had the same value as the 2nd, then the WTHD would have been 0.65% already.
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 8th August 2006, 08:57 PM   #14
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thank you steven.
I know that 2th harmonic sounds "good", 3rd is "sharp"
and 5th is "bad" becouse is apsolutly out of tune...
but I`d like to know what I must have in mind about harmonics when I design an amplifier stage, what level of what harmonic is unacceptable, what is the "best" level difference between 2nd and 3rd harmonic....
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Old 8th August 2006, 09:14 PM   #15
Steven is offline Steven  Netherlands
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Some reading about harmonic distortion and audibility:

A NEW METHODOLOGY FOR AUDIO FREQUENCY POWER AMPLIFIER TESTING BASED ON PSYCHOACOUSTIC DATA THAT BETTER CORRELATES WITH SOUND QUALITY
(Thesis form Daniel H. Cheever)
It can be downloaded here: http://w3.mit.edu/cheever/www/cheever_thesis.pdf


Small-Signal Distortion in Feedback Amplifiers for Audio
by James Boyk and Gerald Jay Sussman
It can be downloaded here: http://www.its.caltech.edu/~musiclab...er-acrobat.pdf
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 9th August 2006, 05:14 AM   #16
jcx is offline jcx  United States
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Don't read Cheever's thesis - he abuses too many concepts and will leave your understanding of the subject in negative territory - you will have to "unlearn" almost anything you think you've understood from Cheever

please Don't recomend Cheever to anyone - especially someone without experience and background
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Old 9th August 2006, 08:43 PM   #17
Steven is offline Steven  Netherlands
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Ok, some others then:

http://www.gedlee.com/downloads/dist...perception.ppt
http://world.std.com/~griesngr/intermod.ppt
http://www.zainea.com/multidimensionalaudio.htm
http://www.nutshellhifi.com/library/FindingCG.html

Actually a lot of articles on:
http://www.zainea.com/soundandmusic.htm
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 11th August 2006, 03:40 PM   #18
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by jcx
Don't read Cheever's thesis - he abuses too many concepts and will leave your understanding of the subject in negative territory - you will have to "unlearn" almost anything you think you've understood from Cheever

please Don't recomend Cheever to anyone - especially someone without experience and background
Hi,

I found the first chapter a good overview.

The second chapter - fairly pointless.

/sreten.
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Old 26th April 2010, 05:22 PM   #19
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Default Import from P-Spice Parameter of new devices (Text files)

need a little help for follow task: the import of P-Spice parameters from new BjT power devices - e. g. Onsemi's MJL4281:
ON Semiconductor

in the instruction manual (Chapter 9) I read only this:
Import > Simulate Spice Netlist
Use this option to import and simulate a Spice netlist that you might have created in another simulation program. When you use this feature, CircuitMaker does not display the actual schematic drawing. Instead, it runs the simulation, displays the analysis window, and places a Waveforms list at the bottom of the Panel which you can use to choose different variables to plot. SVGA display is a minimum requirement to access the Waveforms list. See Figure 9.1 in the user manual about

http://www.gel.usherbrooke.ca/ste/st...usermanual.pdf

But about the import for new models I don't find the appropriate chapter

What is the right way?
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Old 28th April 2010, 08:29 PM   #20
Steven is offline Steven  Netherlands
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Default Import Spice models

In chapter 17 you'll find a section 'Working with Spice Models' with some subsections about editing Spice Models.

Steven
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