Total Harmonic Distortion

Can anyone tell me about what this really means? I've seen listed spec's for equipment that lists TDH as less than .1%, < .05% and even 3 digit like <
.003%. I understand than lower is better, but does >.05% mean half as much as <.1%? or 5 times more than <.01%? Sometimes I think people just put in extra 0's behind the decimal point.

My understanding is that the math is relatively simple... as you described.

A more interesting question is whether you can hear these differences, and what impact lower distortion levels have on sound quality.

I have heard a number of folks suggest that .5% THD is roughly the point where an experienced listener can detect audible distortion... in the form of clipping.

Also, consider the cumulative effect of THD in the various audio components in the chain... source device, then pre-amp, amplifier, and finally speakers.
As the signal passes through the various stages, is the effect simply additive, or even worse, is there a multiplier effect?

Not all manufacturers measure THD in the same way.

Unless both components are measured in the same way the figures are meaningless.

Examples;

1 channel at full power @1khz
both channels at full power @1khz
1 channel at half power @1khz
both channels @ half power with white/pink noise
and many other variations.

What does 'clipping' sound like ?

And while we're at it what is clipping technicaly?

matel said:

What does 'clipping' sound like ?

And while we're at it what is clipping technicaly?

Click to expand...

Sound like? Odd order harmonics.

Technicaly speaking? When an amplifier is pushed to create a signal with more power than it can support, it will amplify the signal only up to its maximum capacity, at which point the signal will be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping." The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a distorted waveform.

Many electric guitar players intentionally overdrive their guitar amplifiers to cause clipping in order to get a desired sound.


All amplifiers have a maximum amount of power, so theoretically they all can clip. However, many amplifiers will not allow a user to turn gain up beyond that point, so that the amplifier never clips. This is sometimes to reduce accidental distortion, or more importantly, to keep from damaging the amplifier as some amplifiers cannot withstand the heat generated by some forms of clipping.

In power amplifiers, the signal from an amplifier operating in clipping has two characteristics that could damage a connected loudspeaker:

Because the clipped waveform has more area underneath it than the smaller unclipped waveform, the amplifier produces more power when it is clipping. This extra power can damage any part of the loudspeaker, including the woofer or the tweeter, by causing overexcursion, or by overheating the voice coil.
In the frequency domain, clipping produces strong harmonics in the high frequency range. The extra high frequency weighting of the signal could make tweeter damage more likely than if the signal was not clipped. However most loudspeakers are designed to handle signals like cymbal crashes that have even more high frequency weighting than amplifier clipping produces, so damage attributable to this characteristic is rare.

There, I must sound like an expert. Actually, I copied that from Wikipedia.

That was pretty clear, I understood some of it !

Hpsenicas question of how closely low distortion
and sound quality are related and why seems very interesting.

Clipping sounds metallic and raspy- not pleasant at all.
Amplifiers produce all sorts of nasty harmonics and spurious high frequencies when pushed into clipping, some amplifiers are a lot worse than others. Many amplifiers are unstable into clipping and can self destruct or oscillate out of control. THD and clipping are unrelated. Tweeters can and often self destruct with amplifiers that clip.

I might try and explain clipping from my own limited understanding. Lets pick a tube, an amplifier, a triode. The tube is biased so that when idle the electron flow from the cathode to anode is in the middle of it's operating range. A tube is selected so that whatever signal is going to be amplified, when added ( at the grid ) to the electron stream won't push the tube beyond it's operating range (clipping). That part of the signal that pushed the tube beyond it's operating range is clipped, chopped off, the wave is no longer sinusoidal.