Peterson AutoStrobe 490ST User Manual download pdf (Page 31)

Page 37

APPENDIX A:

WHY USE A “REAL” STROBE TUNER?

There are many cheap “strobe pattern” tuners on the market which attempt to emulate the look of the image produced by an

authentic rotating strobe disc. This is usually done with an array of LEDs (Light Emitting Diodes) which are simply turned

ON or OFF in sequence so as to “appear” that the light image is drifting left or right.

While such schemes may satisfy an economic niche, they miss out on the almost magical (and supremely functional) aspects

of a true strobe effect. All of these emulation schemes necessarily have one thing in common: a digital decision must be

made to interpret when to indicate an “in tune” signal (either by lighting a special green LED or otherwise creating a non-

sequencing pattern on the LEDs). This creates several problems.

The most glaring of these is the “dead band” problem. The circuitry to form an “In tune?/Out of tune?” decision can, indeed,

be very simple and cheap but, by its very nature, it implies that some amount of “out-of-tuneness” must be tolerated when

making an “in tune” indication. This is because a frequency that is EXACTLY in tune is an infinitely narrow point. If a

circuit could be made to react to only this point (which is impossible by the way), getting that treasured “Green LED” to turn

on would be even more of a frustration than it already is on such tuners. In fact, given the normal pitch fluctuations in a real

instrument, the light would simply never be ON (or at best be turned on for such short periods that you would never see it).

As the manufacturers of such tuners widen the band of “out of tuneness” around that ideal frequency—the deviation from

perfect tuning that they decide is “in tune enough” for you—a more stable indication is made. Note that this is at the expense

of your ever knowing how close or far from perfect tuning you are up to the limit of this “dead band”. Such devices typically

give up at about ±1 cent



deviation and usually allow several times this degree of inaccuracy before the “in tune” signal

reverts to an “out-of-tune” indication. Of course, the really bad news is: the total worse case error is double that. (You could

tune your instrument near the sharp end of the dead band, another player might land near the flat end.)

How bad is this level of detuning? Pretty bad! Over the centuries, many have wrestled with the concepts of intonation and

temperament—the art of setting appropriate pitch intervals for the various musical notes. As it happens, there is no one

temperament that allows for truly in-tune musical intervals over multiple key signatures. The level of concern in these cases:

as small as 1 or 2 cents! For example, music in modern western culture is overwhelmingly based upon equal temperament



We have grown accustomed to some of the inherent inaccuracies of this temperament, yet it does present problems. For

instance, one of the milder imperfections is the production of intervals of fifths which are between 1 and 2 cents flat from

“perfect” non-beating intervals (...and you don't even want to know how bad the thirds are!) In many cases, this is quite

acceptable. However, with harmonically rich instruments—a brass section or an electronically distorted guitar, for

example—even this level of detuning can be disturbing. (Good brass players actually adjust the intonation of the notes they

play to minimize this problem. This is why “a good section is hard to find!”) In the case of the guitar where such on-the-fly

adjustments are impossible, adding another couple of cents inaccuracy because of tuning device limitations can yield

positively raucous results. In the orchestral case, the added imprecision could spread the instruments out to the point that

even accomplished players would have difficulty “lipping” the notes accurately. Of course, with their limited precision, the

pseudo-strobe tuners have no hope of properly distinguishing between temperaments. The best that they can do is center

on equal-tempered notes (with their particular shortcomings) and lop on a “dead band” for good measure.

The magic of a true strobe lies in the responsiveness and “smoothness” of the effect from “flat” to “perfectly in tune” to

“sharp”. Physically, no change of state occurs in the tuner—no discrete decision takes place. Your eye simply interprets

the effect of the spinning pattern in relation to the blinking illumination behind it. Thus, the response to the user as the input

pitch is adjusted is literally at the speed of light! This is a perfect visual analogy to the effect of hearing two sound sources

“beat” against each other when they are out of tune. Moreover, your ability to discern movement in the strobe image

(indicating an out-of-tune audio source) is actually more sensitive than that of hearing audio beats and much more sensitive

(about 10 to 20 times more!) than “pseudo-strobe” tuners. This level of precision in your Model 490-ST tuner not only

allows unprecedented accuracy in tuning to “standard” pitches, but permits one to utilize the subtler shades of altered

temperaments—both pre-programmed and user-programmable—discussed in the SETUP section of this manual.

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Peterson AutoStrobe 490ST User Manual Page 31

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