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Re: To a certain extent

Posted by Tom Dawson (A) on January 13, 2006 at 22:01:45

In Reply to: Re: To a certain extent posted by Steve Eddy on January 13, 2006 at 18:42:56:

Now, can you tell me just how a capacitor in service say as a coupling cap in an audio amplifier is ever going to see a situation even remotely resembling what you describe above?

You seem to be suggesting that this Mil test does something other than isolate and make easily measurable an ever present AC characteristic of capacitors (which is a silly way to consider a well established MIL test on the face of it, AFAIC). To that extent, you are wrong. All that is necessary to elicit this behavior is to alter the amount of charge on the capacitor dynamically (eg, as with any nonrepetitive musical signal). So, if you listen only to repetitive waveforms or never charge or discharge your garbage quality audio path capacitors in any way, you won't have very much trouble with the deterioration due to dielectric absorption. Otherwise, you're only happy if ignorant or a masochist with any musical signal given dogshit audio path capacitors found in Costco quality audio gear. How to tell if this will be an issue with any given equipment with substandard DA capacitors? Pass a 20 hz square wave through all such circuitry. If there's any perceptible tilt on the top or bottom as seen on an oscilloscope, you'll certainly have audible problems with musical signals from poor DA quality capacitors. This signal deterioration reveals itself to the extent that the capacitor deviates from ideal behavior due to this mechanism, which in audio circuits will be predominantly throughout the lows and midrange (because of Fletcher-Munson weighting and musical energy distribution). To sum up, such a high proportion of everything of musical significance is thusly affected that it makes little sense to quibble over the remainder. Several percent of the musical dynamic peaks of this effect is a huge amount, requiring cloth ears, a really bad system (setup) or a mule-like obstinacy not to perceive or to persist in refusing to acknowledge, given the 30 or 40 db dynamic range typical of decently recorded actual music.

Further, can you tell me exactly what the actual effect on an audio signal would be as a result of a capacitor behaves as you mention in the original post?

It's erroneous, unrealistic and overly simplistic to presume that there will be 'exactly' only one perceptible 'actual effect' on the nearly infinite variety of nonrepetitive musical signals from such a mechanism as this, as I'm sure any rational person will agree, given a moment's thought. However, I've already indicated some of the primary subjective effects from poor dielectric absorption performance several posts above, but it's not hard to imagine the deleterious impact during a quiet passage 30 or 40 db lower than a preceding transient peak if the instantaneous waveform deviates several tens or hundreds percent from where it ought to because of delayed energy released from dielectric soak, even more deleterious when interchannel cues are part of the information intended to be processed.

Keep in mind that this is technically a problem with energy storage where a portion of high level signals is delayed as subjective noise during later lower level signals, thus providing both a 'smearing' and 'dynamically compressive' effect. Of course, one can wave his fairy wand and pretend there's no consequence from poor dielectric absorption capacitive performance in audio circuits (as opposed to any other even mildly critical AC application a competent engineer could imagine), but there's no help for such a person in an audio forum.

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