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Old 20th June 2013, 11:25 PM   #101
jcx is online now jcx  United States
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I like looking at the FFT plot, and with multitone excitation - THD really doesn't do much for me
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Old 21st June 2013, 06:12 AM   #102
Mooly is online now Mooly  United Kingdom
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I haven't, its interesting but I've to much on the go at the moment to take the time to figure it all out
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Old 24th June 2013, 08:43 AM   #103
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Originally Posted by jcx View Post
I like looking at the FFT plot, and with multitone excitation - THD really doesn't do much for me
this is exactly like me
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Old 24th June 2013, 08:48 AM   #104
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Did you guys try the THD Analyser? Seems like an interesting approach, even for non-LTSpice user like me ;-)
no, unfortunately not,
it seems for me too difficult find to downloading it, then put to the right place in ltspice, and then setting those parameters
however I can see that this is very helpful thing!
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Old 24th June 2013, 09:11 PM   #105
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Originally Posted by padamiecki View Post
this is exactly like me
Could you guys post some example of the FFTs with multi-tone, are you using any particular standard such as SMPTE, CCIF, etc.?
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Old 25th June 2013, 01:08 AM   #106
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The simplest multi-tone analysis is just two sine waves, frequency shifted so they heterodyne to make a signal with a sine-shaped envelope. This is basically the same thing as a sine-burst signal. Here is a amp test rig I made set up for CCIR.

If you want to do multi-tone analysis you must really remember the "noise floor" in SPICE doesn't mean anything, and it has to be low enough before you will get meaningful results. A high noise floor in simulation indicates the simulator is not set up optimally. This rig attempts to correct that.
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File Type: asc ampsim5_CCIR.asc (6.3 KB, 17 views)
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Old 25th June 2013, 01:14 AM   #107
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Originally Posted by keantoken View Post
The simplest multi-tone analysis is just two sine waves, frequency shifted so they heterodyne to make a signal with a sine-shaped envelope. This is basically the same thing as a sine-burst signal. Here is a amp test rig I made set up for CCIR.

If you want to do multi-tone analysis you must really remember the "noise floor" in SPICE doesn't mean anything, and it has to be low enough before you will get meaningful results. A high noise floor in simulation indicates the simulator is not set up optimally. This rig attempts to correct that.
Thanks, this is very useful information.
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