[QUOTE=DrShaggy;4725946]Aaalaa Taimoor bhai, replied like an engineer 
I dont think there is much left for me to add even if i wanted to. Kaisay ker letay hain aaaaaaap taimoor bhai..kaisay??? 
Just to make it easier for people like me to understand and imply it in real life, THD is the sum of the original signal supplied to the amplifier and the additional (sometimes wanted sometimes unwanted) noise added by the amplifier or any other equipment in the signal path for that matter. Ideally the perfect equipment, be it an amplifier, HU or a DSP shouldn't add any other noise etc to the original signal and thus have no distortion but as we know, the world isn't perfect :P So, each amp etc DOES add distortion or noise to the original sound. And THIS additional noise or THD or distortion is what gives each amp etc its own sonic characteristics.
Another thing is what these numbers printed by the manufacturers mean in real life and how they should affect the decision to buy or not a specific piece of equipment. Most people believe that a lower THD number represents a better amp and mostly it is correct. Quality amps etc have THD too low to be audible or to be perceived. But, while THD is attributed one of the "measurable" aspects of a amplifier etc's sound quality, it however doesn't directly imply that an amp with a lower THD level is better than amp with a higher THD number (which is measured in percentage). Commonly the manufacturers are not too honest with their stated THD digits particularly they don't mention the measuring conditions and parameters as Taimoor bhai pointed out. The more meaningful number is THD+N which most manufacturers conveniently omit. Usually it is measured at 1khz frequency alone. And truth is THD is different at different frequencies and at different power levels. Another interesting fact is pertaining the human perception of distortion or THD. Listen to a 1khz tone with 1% THD and you can easily pick out distortion affecting the sound. But, turn on some music and you will have a hard time even pointing out THD levels upto 5% ;) In a car install environment particularly, HU, DSP or amplifier's THD levels should be the least of ones concerns distortion-wise. The most distortion inducing elements in any system are the speakers themselves! With the subwoofer being the most distorted element in the system, sometimes upto 15% even.
Rest if someone wishes to know more about THD in technical terms, @roms bhai can help them out by shedding light on the technical stuff because you know what they say about engineers, "they do it with precision" ;)[/QUOTE]
There you go @blacklist1
Sticky notes for all noonbs and "wanna be audiophiles"
Too good shahid bhai
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