The page you linked to had no subjective listening tests.Hugh Jazz said:
Or the cap is good enough to do its job without audibly damaging the sound i.e. most coupling caps. You seem to assume that a cap must damage sound in an audible way; why?
Yes, of course, provided that it was a listening test and the cap was so poorly used in the circuit that distortion was audible. His test was objective using test equipment, so a DC bias would simply have changed the pattern of distortion products if the caps were producing distortion.
I don't understand your point. Given that most caps can do the job of a coupling cap very well, we learn nothing from exploring strengths. We only learn from what the cap (in that circuit) fails to do well. We know that all coupling caps will eventually cause problems at high enough signal levels and low enough frequency so that is where we look to grade them. If two caps pass even that test then we know that they are both good enough to be used as a coupling cap and there is no point in buying the more expensive one, apart from bragging.
Why specify a DAC with no filter? Do you want to pollute the test with images?
You would be measuring a cap feeding a particular amp input, not measuring a cap. You would need to ensure that all the caps had the same capacitance value - many 'cap tests' fail on this issue alone. The big problem with measuring coupling cap behaviour is that almost everyone who has the knowledge and equipment to do it properly also has the knowledge to know that it is not worth doing.
Now capacitors used as filters, that is quite different; that is where some difference would begin to emerge, but even then it would be a smaller difference than imagined by some people.
You would be measuring a cap feeding a particular amp input, not measuring a cap. You would need to ensure that all the caps had the same capacitance value - many 'cap tests' fail on this issue alone. The big problem with measuring coupling cap behaviour is that almost everyone who has the knowledge and equipment to do it properly also has the knowledge to know that it is not worth doing.
Now capacitors used as filters, that is quite different; that is where some difference would begin to emerge, but even then it would be a smaller difference than imagined by some people.
My proposed test is just an embryo thought, with the idea of listening to just one cap with/without a bypass, not the accumulative effect of many, based on a counter to your assertion - that caps don't all do the job of coupling equally well. That is the test, to explore relative strengths, which perhaps is an exercise for the reader, because I prefer DC coupling anyway. Caps are not wires.
He refers to the subjective testing on that page and he posted a link to it iirc too.
Let us say you listened to a particular coupling cap in a particular circuit with and without a particular bypass, and you preferred the sound with the bypass. What objective facts does that give us? Your preference is just that, a preference; you might like music with a small suckout in the upper HF region. To establish a useful fact you would need to show that a bypassed cap was actually better at getting undamaged music from one side to the other, which presumably means you have first established that the unbypassed cap is worse than a wire (apart from the unavoidable LF rolloff, which may be the most audible sign of the presence of any cap).
I think the problem you face is that if you assume that any coupling cap will damage music then you have already decided to deny what circuit theory says so you are in the realm of alchemy. There is then no basis for discussion with others who accept circuit theory, and no real basis for actually designing any audio equipment.
I think the problem you face is that if you assume that any coupling cap will damage music then you have already decided to deny what circuit theory says so you are in the realm of alchemy. There is then no basis for discussion with others who accept circuit theory, and no real basis for actually designing any audio equipment.
Speaking of Alchemy, it is possible to turn lead into gold. Way back when, they were just trying the wrong things.
But the ways of medieval alchemy are not the only way to move forward sans circuit theory. One can scientifically show there is a preference effect for one sound over another without theorizing about some underlying physical mechanism.
Where people may get into trouble is when incorrect attributions of causation come to be believed as physically factual.
I would say don't let DF96 convince you only circuit theorists can claim that something appears to affect sound quality. However, if something is believed to affect sound quality, one probably has some duty to one's self and to others who may become misled if claims of some factual real difference are made without any blind testing at all. One should at least blind test one's self honestly first. Either that, or qualify claims of sound altering effects as casual listening impressions.
But the ways of medieval alchemy are not the only way to move forward sans circuit theory. One can scientifically show there is a preference effect for one sound over another without theorizing about some underlying physical mechanism.
Where people may get into trouble is when incorrect attributions of causation come to be believed as physically factual.
I would say don't let DF96 convince you only circuit theorists can claim that something appears to affect sound quality. However, if something is believed to affect sound quality, one probably has some duty to one's self and to others who may become misled if claims of some factual real difference are made without any blind testing at all. One should at least blind test one's self honestly first. Either that, or qualify claims of sound altering effects as casual listening impressions.
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Moved to the Lounge. OT posts removed.
"The company I work for spent a lot of time investigating capacitors for coupling low-level signals.
We found some interesting things I thought to share:
1. Electrolytics and, in general, most capacitors with "wet" dielectrics seem to have non-linear transfer functions with regard to signal amplitude linearity.
We noticed as you vary the charge applied across the capacitor, you get a different voltage/current transfer characteristics. Keep in mind this is low power, around 1mW or less experiments. So we decided to keep these types of capacitors for non-critical applications, that is out of the signal path.
With a DC bias the characteristics are better but still far from the ideal capacitor.
2. Then we looked at the Metallised capacitors MKT, MKP (Metallised Polyester and polypropylene etc). These are quite good compared to the ones above, in that their transfer functions are quite linear, but at small signals levels around the zero crossing of the audio signal these capacitors are highly non-linear. We first experience this problem when we discovered a non-linear operation of a VCO circuit's control loop response.
We contacted the manufacturer in Germany and we worked out the problem was to do with electron charge movement and the electrochemical potential of the compound needed to be reached in order to get the electrons to move back and fourth, this causing the non-linear response.
Putting a DC bias on the capacitors alleviates this problem.
But the noise of the Metallised component can be a big problem especially if you use it on the input of a high-gain amplifier.
Then we looked at Tantalum capacitors, because of their small size and high capacity; their impedance characteristics are quite good. Most Electrolytics, common garden types, present an inductive component around 1kHz which will usually dominate the impedance characteristics by 20Khz - making the capacitor quite useless. (That's why it's quite a good idea to shunt the electrolytic capacitors with a 0.1uF polypropylene, that is still predominantly capacitate at 20kHz and beyond, but eventually will be inductive, but outside the audio range. But you also have two noise sources, and more distortion - you don't get something for nothing I think.)
The Tantalums we bought from three manufacturers had characteristics better than all the Electrolytics but worse or average compared to the Metallised capacitors.
Also their power dissipation is poor since small surface area, this heats the capacitor, even just 0.5 degree C, will change the characteristics that we measured.
So this capacitor was OK, but expensive, and quite temperature sensitive, more so than you might think.
Solid tantalum dielectric is more stable than the cheaper wet electrolyte types.
Next we looked at the simpler dielectrics of polyester and polystyrene and polypropylene.
To make it short, the polyester is okay, but is non-linear a small amount but the nature of the dielectric means it is poor performing at 10Khz and above. Also it has high noise voltage that is temperature dependent. Similarly capacitor value stability is questionable.
The best by far, we think, is polypropylene. It has the best transfer function characteristics, quite low distortion, and is very temperature stable compared to others, and works well at High frequencies.
They are expensive, and large for their size.
You can get better performance by parallel use of these capacitors to achieve a certain value, rather than using one of those values, but be sure to apply a voltage across the "bank" so that the charge potential is equally placed across the capacitors. This is still good, even though the characteristic of the capacitor may vary. Also you get more noise with the bank, since the noise sources add in magnitude, sometimes it is better to use one cpacitor and put up with the performance if the noise is a problem.
Polystyrene is number two after polypropylene.
Even you can get this information if you read the databook from Wima, Rifa, or Beyschlag, but we wanted to be sure for ourselves."
Bold added for your benefit. Discuss. (over cigars and brandy since we are now in a rather revolting sounding place called the Lounge)
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Well known for electrolytic coupling caps, which is why competent designers who need to use electrolytics as coupling caps simply use 10x or 20x the value calculated for the desired LF rolloff.
I find this hard to believe. Maybe the caps were faulty?
Not true. Yes, inductive. No, not "quite useless" - as I said, a coupling cap merely has to maintain a sufficiently low impedance; it does not matter one whit whether that impedance is capacitive or inductive.
Actually, that is precisely why it is almost always a bad idea to shunt an electrolytic with a film cap. Why artificially raise the impedance of something which is intended to have a low impedance? In many cases it will do little harm, as being a coupling cap is an easy job for most caps (including electrolytics) but it is unlikely to do any good.
Thank goodness for that. Based on seeing these discussions repeat over and over again over the last, well over a decade (!) I knew it was futile and said so. Thankfully this thread can now serve as evidence of that, if nothing else. Next time someone else starts this up, I can just link to this thread. Not completely wasted time I hope.
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