A lot of the old Irish fiddle music was actually originally intended for the harp. If you want to know what it sounds like, I highly recommend Patrick Ball. http://www.amazon.com/Celtic-Harp-Vol-Turlough-OCarolan/dp/B...
(I don't know what tuning he is using. I strongly suspect equal temperment.)
This is what Hacker News is all about, in my opinion.
I generally tell pianists to keep their left hand out of my octave and no one will get hurt.
It's really frustrating to try and figure out the precise notes - but I can improvise fairly well on my own or with another string. I definitely need to train my ear better, but knowing that there's this interval problem now - it'll probably help, because I know that there's something I'm going to have to adjust for.
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Who votes these up? Don't we all know by now that clicking the "Print this article" or "Single page" link on a multi-page article will transport us to that magical single page?
(In case you're wondering, I didn't vote the parent down.)
I kind of had the feeling that someone is jumping to the karma conclusion. Woe. Woe, I dare to say.
Oh, and if I said I didn't appreciate the karma, I'd be lying. The +3 boost this is giving me puts me at 660, and I'm annoyed when my karma isn't divisible by 5. (I'm serious)
Otherwise I don't really care. In fact, I often post riskier comments if my overall karma isn't divisible by 5. If I was at 901, and someone somewhere downvoted me to 900, it would make me happy.
So please don't screw up my karma, you'll make me sad.
Addendum: I do appreciate that "divisible by 5" quirk you mentioned :).
My quirk seems to be that I don't really consider my comments complete until I've reread and edited them something like 5-10 times. I thinks that's why it makes me kind of sad when my shortest comments (e.g. http://news.ycombinator.com/item?id=1283979 and http://news.ycombinator.com/item?id=1219118) are the ones that get the most upvotes... I spend so little time on those comments, as compared to one like http://news.ycombinator.com/item?id=1284130.
I also remembered that I hate touching my mouse, and I prefer to keep my ring finger on "page down" when reading on a computer. Having to physically lift my hand, move it to the mouse, find the cursor on the screen, aim it at "next page" or whatever then click, and if I misfire... start over. This really breaks my flow and is quite disruptive.
I know I'm not the only one who cares about stuff like this.
But in this case the printer friendly version omits the sound clips, which are what make the article.
When I'm reading HN on a phone or other high-latency environment I appreciate saving the extra roundtrip.
It includes music featuring some really intriguing concepts. For example, "Three Ears" isn't played in a fixed scale at all - instead the tuning is tweaked on the fly "for maximum consonance". The result is weirdly fascinating.
I don't know if its the tunings or something in the recording/mix process; nevertheless I'm going to seek out the cd recordings - thanks for sharing.
I've read about this (temperament) many times, and I still have no idea what they are talking about, and I assume it's because I just can't hear the difference.
I'm not tone deaf, but I guess I'm not very good at tones.
(1) Axiom: We hear at a logarithmic scale. What we perceive to be a difference (or interval) between 2 notes is actually a ratio of frequencies. (I think biology may explain this axiom.)
(2) Axiom: Say you hear 2 notes, of frequencies f1 and f2 respectively. When the f1/f2 ratio is a simple rational number (like 2) or (3/2), it sounds good. When the ratio is more complicated (like 19/17), it sounds worse. (Physics can explain that axiom.)
(3) Definition: when the f1/f2 ratio is 2, we call that an octave. The 3/2 ratio is a fifth. The 4/3 ratio is a fourth. As a side note these ratio were basically the only ones that were used. They didn't really used thirds or sixths, probably because of their more complicated ratios, which may have sounded bad to their ears. 
(4) Theorem: There is no way in hell you can make an octave out of fifths (they won't perfectly tune together). Informal proof: this is because you can't find any (i,n) ∈ ℤ², such that (3/2)ⁱ = 2ⁿ. As a side note, you can come relatively close: (3/2)¹² = 129,75 which is close to 2⁷.
So, a mathematical impossibility prevents you to perfectly tune the two most basic intervals ever. Ouch. We have to compromise, then. We can sacrifice a few chords (which if played will cause severe ear damage); or cheating a little bit on every ratio, so no chord sounds outright wrong, nor exactly right; or we can try to find a middle ground between these two extremes.
The "sacrifice" strategies was originally favoured. They sounded better, but restrained what you could play. Now, we favour the "cheating a little" strategy (also called "equal temperament"). They give you more liberty, but sounds rather dull on old music meant to be played with an old fashioned tuning (to trained ears, at least :-).
Hope this helped.
: http://pipolitics.com/video-streaming/kaamelott-saison-2-epi... is an excellent joke on the topic. (This is a flash video in French, unfortunately. I hope you understand it, or can find a friend who does).
What about the ratio of two notes played on after the other? Is that very important too?
Could you make a piano with multiple keys each tuned to match a particular ratio better?
I'm not sure the ratio of two notes played one after the other really counts by itself. However in many instruments, two consecutive notes will tend to overlap (piano, for instance). Also, many instruments (especially those with strings, like claviers and violins), resonate better when the note you play has a "good" ratio with the natural notes of the instruments, even if you don't play them! Some instruments were even designed around this principle. So you have to maintain a good ratio with respect to these "base" note at all times.
In practice, the ratio of two notes played one after another is indeed important.
I'm not sure I understand your last question. Actually, you can change the tune of a piano. So, the optimization you speak of is possible even on a modern piano. Just re-tune it.
A final note about why "simple ratios" sound better: When you make a string resonate, it doesn't do only one note. It does its base frequency (say f), and many others (every multiple of f). So, in a piano, when you play a G at 100Hz, it also plays at 200Hz (a G), 300Hz (a D), 400Hz (a G) etc. Note that there exist actual keys whose main frequencies are 200Hz, 300Hz, 400Hz and so on. They will resonate, which will make the sound richer, louder.
The problem with equal temperament is that the only ratio which is really respected is the octave (2 to 1). In such a case, the D I mentioned above won't be quite at 300Hz, and won't resonate well. So equal temperament became practical only when instruments became loud enough to make up for the loss in resonance.
Equal temperament uses frequencies that are scaled by powers of the twelfth root of 2. Moving up one semitone is the same as multiplying the frequency by 2^(1/12). If you look at this table
you can see how the resulting values approximate certain ratios. Ratios matter because two tones that are related by a simple ratio will tend to have greater harmonic relationship and be more 'consonant'.
Other tunings emphasize different ratios and give up the equal spacing of notes -- equal spacing when plotted by frequency on a logarithmic scale.
It sounds pretty good, actually, but so do plenty of other temperaments.
(Of course, at >$3000 I'm not actually going to buy one. Just geek out over it.)
How hard is it to vary tunings with existing synthesizers?