Tuners: accuracy vs. precision...

[FrankS]

Once you settle on a tuner that you feel is super excellent in precision and accuracy, take a stroll down the fretboard and see what you think. Even going from the nut to the first fret will show a great deal of tuning differences on most guitars. Take one of your best songs that you recorded and play it back with digital looping so the tuner has time to lock onto the tone. You may be surprised at how far sharp and flat your best of notes are even with "perfect" tuning at the nut. Some of this is inherent in the fret spacing but much has to do with technique itself too.

Frank Sanns

[devellis]

Originally Posted by HHP

Does averaging work when you know you have an absolute to deal with such as the temperature at which the chemical explodes. You are OK on one side of the variation and vaporized on the other.

In the case of the guitar tuner, you would seem to be working to match an absolute like A440.

Constructing a scenario in which measurement failure has critical consequences doesn't change how measurement works. It just requires that it work better if a disaster is to be averted. Bias and consistency are fundamental aspects of measurement. If one considers a single outcome rather than a set of outcomes, all bets are off. Probabilities aren't defined in the single instance (kind of like division by zero isn't meaningful). Single instances have binary outcomes -- 1 or 0. How likely is it that I will die of cancer? Either 1 or 0. I will or I won't. On the other hand, for people like me, probability estimates are continuous between 1 and 0 with increasing precision as the sample size and appropriateness of the sampling frame increase. Similarly, a single shot is either a hit or a miss. The shooter may have aimed badly but a random error or bias may just exactly compensate so that a hit results. Or the same error sources may result in a miss when the aiming is good. The single instance isn't informative with respect to the measurement (although it can certainly be consequential with respect to the outcome). If one shot hits or misses a target, you can't say anything about the accuracy of the sights or the quality of the gun. You don't know what accounted for the outcome (although some scenarios may be more likely than others because the area of non-target is larger than the area of target). But with repeated observations, you can determine what factors (gun, shooter, their interaction, wind, etc.) are driving the outcome to various extents.

Precision and accuracy, as we are discussing them are not a trade-off. They are independent. A wide scatter or a narrow scatter can both average to either a "true score" or to an error. However, if the focus is on the achievement of an accurate prediction, they are dependent, with precision setting a limit on the likelihood of "success". In the context of reliability/validity, the validity coefficient can't exceed the square root of the reliability coefficient. This has to do with the theoretical relationship of observed scores to true scores.

WARNING -- UNLESS YOU"RE REALLY INTO THIS DISCUSSION, YOU MIGHT WANT TO SKIP THIS NEXT PARAGRAPH:

Reliability, in techno-speak, is the proportion of variance in a set of observations that arises from the state of the entity being measured (e.g., the proportion of variance in observed temperature values that arises from actual differences in temperature and not other factors, such as quirks of the measurement tool). If the proportion of variance between an indicator and a true score is .64, the correlation between the true score and the indicator is the square root of .64, or .80. If validity is established by means of camparing the indicator being evaluated to another indicator of perfect reliability (the best case), the latter would have a correlation with the true score of 1.0. Thus, the maximum correlation possible between the measurement and the infallible indicator is the product of the two indicators' correlations with the true score, or 1.0 x .80 = .80, the square root of the reliability. So, the greater the reliability, the higher the possible validity. Note that, in this context, validity is defined in terms of correlation -- the ability to predict the true score. It doesn't imply that the measurement obtained is the same as the true score (think of predicting Fahrenheit temperature from a Celsius thermometer -- excellent prediction even though the numbers are different). The discrepancy between the estimate and the true score is not measurement error but miscalibration. The predictive power isn't compromised by miscalibration but without correcting the miscalibration, the estimate will be off the mark (in completely predictable, nonrandom, ways).

[ecguitar44]

Originally Posted by devellis

But with repeated observations, you can determine what factors (gun, shooter, their interaction, wind, etc.) are driving the outcome to various extents.

I smell a discussion about Gauge R&R right around the corner...

[Long813]

Originally Posted by Landru

Yeah - but one tuner has only one bullet, so why bring precision into the convo? Did you mean six tuners = six bullets? The illustration is precise but not an accurate representation.

Err, it's both, but how one extracts it's meaning is variable.


A precise tuner, will give up the same flat or sharp notes within x +/- cents. If it wasn't precise, one time you strike the b string, its output ends up being 5 cents of, the time time, maybe it's 12 cents off. etc.

Precise readings will give you a result that is consistent (always withing +/- x cents), if not correct.

[FrankS]

Originally Posted by Long813

Err, it's both, but how one extracts it's meaning is variable.


A precise tuner, will give up the same flat or sharp notes within x +/- cents. If it wasn't precise, one time you strike the b string, its output ends up being 5 cents of, the time time, maybe it's 12 cents off. etc.

Precise readings will give you a result that is consistent (always withing +/- x cents), if not correct.

But it may be that far off. What is being left out is time. In time electronics can drift. Also with RF noise. Most of all with electronic tuners that use a quartz crystal reference, they change with temperature and have to be internally compensated for that. Of course guitars do too BUT, it is conceivable to have an accurate and precise tuner at one temperature and it change accuracy at another temperature. It is very simple or should I say, it is very complicated.

Frank Sanns

[drplayer]

Before this goes from the sublime to the ridiculous (possibly it's too late? ), maybe we should try to get this back to the intent of the OP?

Agreed...ideally a tuner should be both accurate & precise. However, what one uses, or how one goes about determining that, is subject to error as well. To ensure accuracy, one would need to calibrate the tuner to some standard that is known to be at near perfection (not likely something most of us have access to). Imprecision, on the other hand, is inherent to each individual device (i.e. tuner), and not generally something that we can improve. Therefore, since true accuracy and precision are for the most part outside of our control and entrusted to the tuner manufacturer, just tune using the method that works best for you, and play, play, play!