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Tuning Precision & Accuracy

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#55 Terry McGee

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Posted 17 March 2014 - 05:36 PM

 

Happy St. Patrick's Day! / Beannachtaí na Féile Pádraig!

 

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Normal service will be resumed as soon as possible...

 

 

Uhhhh.  Pity help anyone who's concertina is getting tuned this morning....

 

Terry



#56 cboody

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Posted 17 March 2014 - 11:32 PM

 

 

Happy St. Patrick's Day! / Beannachtaí na Féile Pádraig!

 

0060-0609-2914-5430.jpg

 

Normal service will be resumed as soon as possible...

 

 

Uhhhh.  Pity help anyone who's concertina is getting tuned this morning....

 

Terry

 

Oh I don't know Terry.  I think I'm with those who called the folks out and about today the "Paddywhackers."  It might be a good day to stay home and avoid one more chorus of Wild Rover or Danny boy...



#57 Stephen Chambers

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Posted 17 March 2014 - 11:48 PM

As a matter of fact I'm stone-cold sober, but I certainly saw plenty of "Paddywhackers" today :rolleyes:, both in Galway and (on my return) in Miltown Malbay. But, back to the topic:

 

My question to Doug about whether he had problems with the way pianos are tuned was a very loaded one, but he hasn't replied to me about that.
 
The reason I asked it is that (if tuned by a trained, qualified, professional piano tuner) pianos are not tuned to "zero" cents on an electronic tuner but by beats, and the octaves are progressively "stretched" (the degree of which varies, depending on the piano) so that (for example) the top C might be 30 cents sharp and the bottom one 20 cents flat - so half a semitone apart! :blink:
 
Which is a very long way off "zero"...
 
Professionals would consider tuning a piano to "zero" cents (on an electronic tuner) to be amateur and incompetant work, and there is great controversy in the piano world about untrained people who are setting themselves up as so-called "piano tuners" and doing just that.


#58 blue eyed sailor

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Posted 17 March 2014 - 11:56 PM

Stephen, that is a thing I never heard of albeit playing the piano over decades until now! I would love to read about as to why pianos are given such a treatment ...

#59 apprenticeOF

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Posted 18 March 2014 - 12:23 AM

Just as there is a wide range of instrument qualities, there is a wide range of customer needs.

 

I spent years working in steel fabricating plants, and I play for own enjoyment, so there would be no need for an instrument for me to be any closer than 2 cents. In point of fact I have one concertina that is tuned A435 and I can't tell the difference from a spot on A440 instrument.

 

Tolerances were often an issue in steel fabricating. When I was doing estimates, they were always quoted "per standard shop tolerances, closer tolerances available at extra cost". We did produce parts bent from tempered steel to very tight tolerances, but at also at very high labor costs - and therefore prices.

 

IF I were to be tuning instruments for someone else, the tolerance might be part of the pricing. E.G. +/- 1.5 cents seems reasonable for lower to mid instruments for amateur players, so "standard tuning" would be price "x", with the option of "precision tuning" for price "y", and possibly "professional grade tuning for price "z". Then the customer chooses, and knows what they are getting.

 

I doubt that many folks would want to spend top dollar for tuning a basic brass reed Lachenal.

 

The one instrument that I had tuned by Concertina Connection (Wim Wakker) came back exactly on. Not one note registered on my computer as being out at all, not even .1 cents.

 

That would be my suggestion, ask the customer. Ok, do you want standard tuning for "x", or do want precision tuning for "y".



#60 Stephen Chambers

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Posted 18 March 2014 - 12:28 AM

Stephen, that is a thing I never heard of albeit playing the piano over decades until now! I would love to read about as to why pianos are given such a treatment ...

 

There's lots written on the subject, as you'll find if you Google piano tuning stretched and (doing that) I see that the first result (from Wikipedia) says "the  total amount of "stretch" over the full range of a small piano may be on the order of ±35 cents" - which is a difference of 70 cents... (The "stretch" needing to be greater in a piano with shorter strings - it's not so bad in a concert grand.)



#61 Terry McGee

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Posted 18 March 2014 - 12:32 AM

For very good and easily understandable reasons, Wolf.  Pianos, being hammered, need thick strings, very thick (or the hammer would stretch the string too far before delivering any useful amount of energy).  A thick string is some way along the path of becoming a rod.  And this thickness and stiffness introduces inharmonicity in its partials - i.e. the partials are no longer harmonics - they tend sharp of the fundamental note.  

 

So imagine the piano tuner tunes all the C notes using a tuner.  And then plays four C notes at the same time.  You end up with a jumble of fundamentals and partials that are in violent disagreement, so the intervals all sound sour.  And because the harmonic series includes lots of other notes (like Es, Gs, etc), chords using those notes also sound bad.  

 

So, traditionally, the piano tuner starts by tuning a central note from a fork or tuner, then setting the central octave of notes by counting beats, then tuning outwards in both directions by ear.  When you play two C notes an octave apart, the ear is not comparing C4 to C5, but the C5 partial of the C4 note with the real C5 note.

 

These days, tuners can make use of technology such as strobe tuners.  The strobe on the lower note can see the C5 partial of the C4 note, just as we can train ourselves to hear it.

 

Incidentally, harpsichords, which are plucked, have very long thin strings, and tune normally. 

 

That's the short answer - you'd find heaps more on the topic on the web.

 

Terry


Edited by Terry McGee, 18 March 2014 - 12:33 AM.


#62 Stephen Chambers

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Posted 18 March 2014 - 12:48 AM

In point of fact I have one concertina that is tuned A435 and I can't tell the difference from a spot on A440 instrument.

 

Which is a difference of 20 cents, though that's rather more than the just-noticeable difference (jnd) (the threshold at which a change in pitch is perceived), which is reckoned to be around 8-10 cents.



#63 Terry McGee

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Posted 18 March 2014 - 12:51 AM

The discussion of inharmonicity of piano strings actually brings me to a related question I had wondered about (but haven't investigated).  Do we see any signs of inharmonicity in concertina reeds?  

 

If so, does it approach a level at which we should be discussing stretching?  

 

And do we see any variance of inharmonicity between reeds of different metals, scale lengths or construction?  

 

Does this tell us anything, e.g. why some materials or construction methods are preferred?

 

To put it in context, if a small piano, as reported by Stephen above, demonstrates an inharmonicity of 70 cents over say 6 octaves, or 12 cents per octave, what is the concertina's?

 

terry

 

(See, one good night out at a St Patrick's Day gig, and I can't even spell my name right...)

 

Terry


Edited by Terry McGee, 18 March 2014 - 01:23 AM.


#64 Terry McGee

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Posted 18 March 2014 - 01:22 AM

Even as I re-read my question, I suspect I have an answer.  It probably doesn't matter about inharmonicity in the reed as the partials are probably phase-locked by the switching action of the reed, just as the meandering resonances of the flute are pulled into line by the switching action of the imaginary air-reed.  So the reed might not be harmonious if plucked, or excited electromagnetically, and then amplified or resonated, but we don't do that.  

 

But I'll wait for that to be confirmed by those who know...

 

Terry



#65 blue eyed sailor

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Posted 18 March 2014 - 01:30 AM

Terry, thank you very much for your very understandable outline - that's all fascinating stuff! Never tuned one of my pianos myself except for a single bad string or triplet. And as to "our" reeds, it might be considered that the tines of a Rhodes appear to be in need of stretched tuning too, according to the Wikipedia article as referred to by Stephen.

Best wishes - Wolf

 

edit: Hadn't yet noticed your own answering the question you had imposed... :D


Edited by blue eyed sailor, 18 March 2014 - 02:03 AM.


#66 alex_holden

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Posted 18 March 2014 - 01:53 AM

This is one of the issues that lead to the development of Real Time Tuning Analysis (RTTA) for flutes.  Others were more flute-centric - it's so easy to adjust flute pitch as you play that there is a real tendency to subconsciously do it when you should be trying to be brutally honest.


Thanks Terry, that system sounds really interesting, for a rough first pass at least. You hit on another issue I've found with trying to both sound the instrument and note down the errors myself - the tendency to subconsciously adjust the bellows pressure slightly to bend the error closer to 0. To stop myself doing this I had been considering sounding all the notes blind into a recorder, then playing back the recording into the tuning software.

As you say, unisonoric instruments would be a bit of an issue. Perhaps a foot pedal input that you use to switch between two 'banks' of notes whenever you change bellows direction?

#67 MarkvN

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Posted 18 March 2014 - 02:47 AM

Great thread, thanks!

If a piano is tuned with a streched tuning and a concertina is tuned 'mathematically correct', what happens when they play together? Do they still appear to be in tune with each other, even to the sensitive ear? And does it work the same way for the lower and upper range?

Mark



#68 blue eyed sailor

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Posted 18 March 2014 - 03:33 AM

Mark, let me try to answer based on my newly acquired knowledge: the piano tuning is stretched because we judge the lower tones by their (upper) harmonics, and thus any well-tuned (i.e. according to its needs, and of course applying the same octave tuning) instrument will be in tune with it, as to be judged by the human ear.

Edited by blue eyed sailor, 18 March 2014 - 03:34 AM.


#69 Terry McGee

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Posted 18 March 2014 - 04:06 AM

Great thread, thanks!

If a piano is tuned with a streched tuning and a concertina is tuned 'mathematically correct', what happens when they play together? Do they still appear to be in tune with each other, even to the sensitive ear? And does it work the same way for the lower and upper range?

Mark

 

Clearly we get away with it, so perhaps your question becomes how do we get away with it?  I think there's a number of factors.

 

Firstly, the concertina has a restricted range, so we're not directly comparing notes at the piano's extremes where things get really wide (I wonder if bass concertina players have a different view on that?)  If we take the piano figures Stephen mentioned, it sounds like we are dealing with stretching of about 12 cents per octave.  If we assume that both concertina and piano centre in the same ranges (and I haven't checked that), we're probably only seeing errors between them of around 12 cents.  That isn't life-threatening, although it is dramatically higher than the accuracies our tuner colleagues are routinely aiming for.

 

Next thing on our side is that the piano is a percussive note - a lot of its energy is blown at the start of the note, and the note decays fairly quickly.  So we don't have as much time available to compare pitches as we do with concertina notes that can go on until you run out of air.

 

The fundamentals of the low piano notes are going to be considerably flatter than the concertina, but the partials of those notes will be in tune or much closer in tune, so that's going to help.

 

The partials of the middle piano notes and the fundamentals of the high piano notes are going to be sharp of the concertina, but the decay time of those high partials on the piano is going to be very fast (because of the same stiffness that makes those partials inharmonic), so we have even less time to be unimpressed.

 

So, my feeling is that it IS a theoretical problem, but NOT a practical one.  Indeed, perhaps introducing un petit frisson adds to the fun?

 

Terry



#70 d.elliott

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Posted 18 March 2014 - 04:49 AM

We seem to be moving a little off the initial question of concertina tuning precision, and what a customer/ player should accept or question. Does anyone wish to comment on my proposal (pre the  piano sub-thread) ?

 

Dave.



#71 Terry McGee

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Posted 18 March 2014 - 06:23 AM

I'd suggest the piano sub-thread actually puts your query into an interesting perspective.  It reminds us that errors of tuning in the order of 12 cents per octave are sufficiently disturbing that piano tuners have had to come up with a strategy for dealing with them.  You'd like to be an order of magnitude better than that, say around 1.2 cents.  Hmmm, that's about where you started.

 

Now, I don't think this issue has been covered.  Can we say with any certainty that concertina reeds drift in a particular direction?  Are they more likely to go sharp, or flat, or do they just drift off aimlessly as the mood takes them?  You proposed (if I can remember accurately back that far) a tolerance of +/-1.5 cents, symmetrical balanced about zero.   If it could be established that reeds typically drifted in a particular direction, you might want to bias your range asymmetrically around the zero so that more time or playing might elapse before they escaped the defined region of acceptability.  But again, do we have that data?

 

Terry



#72 Terry McGee

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Posted 18 March 2014 - 06:24 AM

 

 

 

This is one of the issues that lead to the development of Real Time Tuning Analysis (RTTA) for flutes.  Others were more flute-centric - it's so easy to adjust flute pitch as you play that there is a real tendency to subconsciously do it when you should be trying to be brutally honest.


Thanks Terry, that system sounds really interesting, for a rough first pass at least. You hit on another issue I've found with trying to both sound the instrument and note down the errors myself - the tendency to subconsciously adjust the bellows pressure slightly to bend the error closer to 0. To stop myself doing this I had been considering sounding all the notes blind into a recorder, then playing back the recording into the tuning software.

As you say, unisonoric instruments would be a bit of an issue. Perhaps a foot pedal input that you use to switch between two 'banks' of notes whenever you change bellows direction?

 

 

I was still worried about the intrinsic precision available in the Tartini algorithm upon which our two systems are based.  I knew they were good enough for flute, but could they yield anything like the kind of precision that Dave is proposing?  So I checked the thesis.  These words are comforting:  

 

With a steady signal the pitch can be detected accurate to less than 0.1 cents with only 2 cycles. The algorithms were stress tested under fast variations in pitch, volume and different harmonic structure and maintained an accuracy within 5 cents.

 

Rossing, the colleague of my musical acoustics guru Prof Neville Fletcher, puts 8 cents as a just noticeable difference, but that's in pure tones.  We can do better with complex tones and in harmonic context.  The Tartini thesis author feels that 2 cents is a good figure to aim at.  Again support for Dave's proposal. 

 

So, definitely try out Flutini.  Flutini can already show 1 cent deviations.  If you like the general approach, but want more, we can investigate our options.

 

Terry







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