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I have been reading a lot about audio grade capacitors lately, and I cannot find very good information about them. I have read many posts from different sites saying that audio grade capacitors are just a marketing hype, and that there is nothing new inside of them. Is this true? Or is there something special about these audio grade capacitors that I am missing?

If they really are better for audio than traditional capacitors, what then makes them better? Also, what would be a good test circuit to compare the differences between traditional capacitors and audio grade capacitors?

If anyone reading this has experience with audio grade capacitors please share your thoughts and experiences below. I really want to figure out if this is a marketing hype or not.

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    \$\begingroup\$ Connecting the "outside layer" of the cap to the low-impedance connection is 90% of what's left once you have the right size. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 30 '15 at 4:28
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    \$\begingroup\$ Hype... You ask the important question, what makes them different than other capacitors? They may have better leads than average, but that certainly won't improve the audio. It's right up there with "audio grade" fuses. \$\endgroup\$ – Jarrod Christman Aug 30 '15 at 4:30
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Just as Andy says, ceramic capacitors can exhibit microphonics, which is less than ideal in audio circuits. Large value, physically small surface mount MLCC ceramics also exhibit quite profound decrease in capacitance with applied voltage - take a look at this article from Maxim.

This is a very good reason not to use them in filter circuits, where cutoff frequencies will become voltage-dependent. However, as decoupling capacitors you just need to be aware that this derating occurs and consider using multiple parts in parallel, as well as choosing parts with a higher voltage rating (and hence larger physical size) to achieve practical performance close to the nominal value.

I have not read about dielectrics altering their permittivity with applied voltage, but all parts have non-ideal characteristics and understanding them is part of designing well with them. This sales pitch from NIC Components has a useful table showing some of the pros and cons of different capacitor types.

It is important to consider where the capacitor is being used and what kind of signals it will see, however. For example, an AC-coupling capacitor experiencing a fairly fixed bias voltage and less than 1V pk-pk of superimposed signal will suffer less from voltage coefficients than a capacitor in a power output stage experiencing tens of volts pk-pk across it.

Rod Elliott has a very good article on capacitors in audio circuits on his site. His site is also a very useful reference for lots of practical audio circuits and general audio myth debunking.

In general, the most "ideal" performance capacitors are plastic film parts. They are very stable over differing operating voltages and temperatures. However, their size and cost can prohibit them from use everywhere in audio circuits. You need to consider what performance is acceptable and choose the part appropriately. With all that said, "audio grade" components are almost universally bunkum unless they can point you clearly to measurements and sensible physical phenomena to prove otherwise.

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I'm not saying that they are any different to any other capacitor in general but, certainly, some ceramic capacitors can exhibit "certain features" that may make them problematic in some audio applications.

Microphonics is a recognized problem. The capacitor behaves like a piezo electric transducer and, in a sensitive amplifier producing a big audio output, there could be strange effects and possibly it could turn into an oscillator. I would imagine that in a desktop speaker with an audio amplifier built in there may be a few problems to overcome at some frequencies.

Lower grade dielectrics also alter their permittivity with applied voltage and, I can imagine that when handling a large ac signal in a filter circuit this could cause asymmetrical distortion of the waveform. This was taken from a page by Murata: -

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their ESR is relatively constant (perhaps high not low) over a range of frequencies involving audio. this makes them easy to pair with inductors for a range of freqs stable rather than high frequencies.

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