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Contests/Gnit Weekly Challenge Beginner 003 (GWCB003)/Problem 4 Measurement of Frequency Deviations in Equal Temperament Based on the Number of Humming Cycles
Problem 4

Measurement of Frequency Deviations in Equal Temperament Based on the Number of Humming Cycles

Finished
520 ptsLv.5 ElementaryWaves
2026/07/08 21:00〜2026/07/08 21:30
Author: admin02

Problem Statement

Let FFF be the frequency of the reference tone (the standard tone).

According to the tuning system known as “twelve-tone equal temperament,” in which the frequency ratios of all 12 semitones within an octave (the interval where the frequency exactly doubles) are set to be equal, the frequency increases uniformly by a factor of 21122^{\frac{1}{12}}2121​ for each semitone higher than the reference tone.

Let fff be the true natural frequency of a specific note that is three semitones higher than the reference tone. Based on the twelve-tone equal temperament, the true natural frequency fff can be expressed in terms of the reference tone’s frequency FFF as follows:

f=F×(2112)3=F×214f = F \times \left(2^{\frac{1}{12}}\right)^3 = F \times 2^{\frac{1}{4}}f=F×(2121​)3=F×241​

When a specific note was played on an actual instrument, the tuning was slightly off, so the note sounded at a frequency f′f'f′ that was slightly lower than the true natural frequency fff. When this off-tune note was played simultaneously with the note at the true frequency fff, nnn “beats” per second were observed. The number of beats per second is equal to the difference (in absolute value) between the frequencies of the two sound waves played simultaneously.

Here, if we let f′F\frac{f'}{F}Ff′​ be the ratio of the actual frequency f′f'f′ of the offset sound to the reference frequency FFF, the following equation is derived.

f′F=214−nF\frac{f'}{F} = 2^{\frac{1}{4}} - \frac{n}{F}Ff′​=241​−Fn​

When the two terms on the right-hand side are simplified into a single fraction using the common denominator FFF, the numerator takes the form a×214−ba \times 2^{\frac{1}{4}} - ba×241​−b (where aaa and bbb are natural numbers). Determine the values of the coefficients aaa and bbb, and find the natural numbers that satisfy the following input format.

Constraints

  • Frequency of the reference tone: F=440 HzF = 440\text{ }\mathrm{Hz}F=440 Hz
  • Number of beats per second: n=3 s−1n = 3\text{ }\mathrm{s^{-1}}n=3 s−1

Input Format

Enter the product of the two coefficients, a×ba \times ba×b, as a natural number.

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