Amplifier Distortion
From Zanecorpwiki
An ideal amplifier takes in a signal and outputs a signal that has the same phase, frequency, harmonics, etc., but higher amplitude; i.e., with more power. The difference between the input and output power is the gain of the amp.
No amplifier is ideal, and there are lots of ways distortion can happen. The signal can be biased up or down, it can be put out of phase[notes 1], and frequency distortion.[notes 2][1] The most noticeable and common kind of distortion is clipping, where the sound wave is cut off at the peaks because the amplifier cannot drive the output signal to the extreme and flat lines.
One can pay a lot of money to get technically very accurate amplification systems, but the dirty little secrete is that a great deal of distortion is simply not audible to humans. An amplifier rated at 1% total harmonic distortion, or THD would be considered shit by any audiophile, but this is demonstrably the just detectable level of distortion.[2] In other words, an amplifier with 0.05% THD is functionally no better thana one with 0.005% THD.
Audiophiles tend to shy away from double-blind tests because they poke holes in their love of spending money to impress each other[notes 3]. When it does happen, the results are almost always embarrassing. Editors at the Sound and Vision (then Stereo Review Magazine) put together a decent double blind test that used amplifiers all the way from a $200 Pioneer to a $12,000 tube amp that came in four giant blocks altogether about the size of a fridge. The result: they were about the same. Only 54% made the right call between the two. All in all, only 3 of the audiophiles got 60% and the best score was 63%. This means that there was no difference in the sound that was detectable by human ears. No one in the 200+ panel, including 25 audiophiles could tell the difference.[3][notes 4]
Now, this doesn't mean you should always buy the cheapest amp, there are other considerations. Size, power efficiency, total power output, build quality and durability all matter. I myself love the look of an exposed tube amp and might pay for the decor-value at some point--but I'll know it's just for looks. The ultra-high end amps are impressive bits of engineering, but it doesn't matter because the human ear wasn't designed and emcannot/em detect the minute differences between a $200 Best Buy amp and a $12,000 tube monstrosity.
Speakers are harder, but as far as amps go, it's simple: size your power requirements for volume and to avoid clipping in crescendos, and then get the cheapest thing available with decent built quality and durability.
Notes
- ↑ We don't hear phase, but we do hear the interference caused by the primary signal and harmonics. When the phase of the harmonics is not shifted the same as the phase of the primary, that's when phase interference occurs.
- ↑ Frequency distortion changes the pitch of the sound, and can further cause harmonic distortions similar to the phase distortions.
- ↑ You can read some back and forth letters on the subject here. The results of ABX double blind, the first of it's kind done in 1977, can be found here.
- ↑ The ABX double blind did show more detectable differences, but that was 1977. Now-a-days, technology has improved to the point where amplification can be handled by commodity components.
References
- ↑ http://www.electronics-tutorials.ws/amplifier/amp_4.html
- ↑ http://www.dself.dsl.pipex.com/ampins/pseudo/subjectv.htm#4
- ↑ http://www.hometheaterfocus.com/receivers/amplifier-sound-quality.aspx The article makes a mistake in their analysis, or at least the wording. They say only 114 of 212 listeners could tell the difference -- that's 54%. Really, the numbers mean that no one could tell the difference and everyone was just guessing. I believe it's just bad wording as the gist of the article holds out the proper analysis.
