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Re: Good Response Soundmind.

> On the other hand if THD does not tell us much about how an amplifier
> will sound, what "merit" does it have?

For most people an ideal amplifier is not supposed to have a "sound" whether good or bad. It supposed to be neutral and this will be achieved when the distortion is inaudible.

Now many audiophiles do not seek such amplifiers and prefer ones with a more pleasing sound. However, they do not describe such amplifiers as sounding more pleasing but use words like natural, life like, or similar positive sounding adjectives. There is not much wrong with this until they use words like accurate which have a well defined meaning when applied to amplifiers and tends to cause a few people to object.

The merit of THD is principally that it is simple to measure and if well below the threshold of audibility then this form of distortion will be inaudible for the conditions of the test. Unfortunately, these conditions are not always realistic/representative and extrapolating to real conditions is not always straightforward. Hence, for example, it is unwise to simply take a quoted THD figure of below 0.01% (comfortably inaudible in all experiments) and assume that this will be achieved under all conditions when driving a real loudspeaker.

If the THD is at or above the audibility threshold then one would need to look at the individual components to determine the likelihood of audibility or whether the colouration may be perceived as pleasant or not. At this level it is not particularly useful as a single integrated number but a map of the individual components against frequency and power can be useful diagnostic information for people familiar with interpretting it.

> Please lead me to this amplifier, I want to buy it.

Most competently designed solid state amplifiers fall into this category when driving speakers with reasonable loads and operating well away from clipping. Perhaps a more interesting question is how cheap is good enough and, I am afraid, this I cannot answer with any authority since I have not tested or listened under controlled circumstances to the current crop of amplifiers. Nor, obviously, am I aware of a trustworthy source for this information. Nonetheless, sticking my neck out and having a punt it may be around 231 Euros for a 2x150W Behringer A500 amplifier. Anyone else?

> How would an amplifier with audible distortion sound more pleasant
> to a person with a good knowledge of the sound of real instruments?
> Are the distortions making up for something missing in the recording
> process or a shortcoming in the speakers or what? Just exactly what
> are you saying?

For example, most people are familiar with the sound of valve amplifiers and will often prefer the sound of a voice recorded through such amplifiers even though they have audible levels of distortion compared to that of a solid state amplifier. This can occur for reasons such as modifying the frequency response and enhancing the harmonic content of the voice/instrument. The departure from neutral is not making up for something missing but adding to what is present.

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