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<?php |
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declare(strict_types = 1); |
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namespace ExtendedStrings\Strings; |
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class VibratingString |
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{ |
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private $frequency; |
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/** |
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* VibratingString constructor. |
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* |
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* @param float $frequency The open string frequency (in Hz). |
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*/ |
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public function __construct(float $frequency) |
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{ |
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$this->frequency = $frequency; |
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} |
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/** |
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* Calculate the frequency for a stop. |
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* |
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* @param float $stringLength The length of the vibrating part of the |
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* string, as a fraction of the whole string. |
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* |
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* @return float A frequency (in Hz). |
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*/ |
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public function getStoppedFrequency(float $stringLength = 1.0): float |
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{ |
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self::validateStringLength($stringLength); |
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$centsOverString = Cent::frequenciesToCents($stringLength, 1); |
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return Cent::centsToFrequency($centsOverString, $this->frequency); |
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} |
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/** |
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* Find the sounding frequency of a harmonic-pressure stop on this string. |
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* |
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* @param float $stringLength The string length, as a fraction, between the |
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* open string and the stop (either side: both |
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* .2 and .8 would produce the same result). |
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* |
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* @return float The sounding frequency of a harmonic-pressure stop at the |
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* given string length. |
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*/ |
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public function getHarmonicSoundingFrequency(float $stringLength = 1.0): float |
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{ |
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self::validateStringLength($stringLength); |
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return $this->frequency * self::getHarmonicNumber($stringLength); |
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} |
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/** |
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* Calculate the length of this string needed to produce a given frequency. |
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* |
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* @param float $frequency The frequency for which to calculate the string |
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* length. |
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* |
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* @return float |
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* The length of the vibrating part of the string, as a fraction of the |
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* whole string's length. |
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*/ |
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public function getStringLength(float $frequency): float |
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{ |
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if (Math::isZero($frequency)) { |
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return 0; |
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} |
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$centsOverString = Cent::frequenciesToCents($this->frequency, $frequency); |
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return $this->centsToStringLength($centsOverString); |
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} |
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/** |
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* Convert a string length to a harmonic number. |
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* |
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* @param float $stringLength The string length between the open string and |
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* the harmonic-pressure stop (either side), as a |
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* fraction. |
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* |
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* @throws \InvalidArgumentException If the stop is not a sounding natural |
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* harmonic. |
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* |
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* @return int The harmonic number. |
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*/ |
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public static function getHarmonicNumber(float $stringLength): int |
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{ |
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self::validateStringLength($stringLength); |
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$number = intval(1 / Math::gcd(1, $stringLength)); |
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if ($number > 100) { |
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throw new \InvalidArgumentException(sprintf('Invalid string length for a harmonic: %f', $stringLength)); |
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} |
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return $number; |
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} |
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/** |
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* Validate a string length. |
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* |
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* @param float $length |
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* |
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* @throws \InvalidArgumentException If the string length is invalid. |
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*/ |
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public static function validateStringLength(float $length): void |
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{ |
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if ($length < 0 || Math::isZero($length) || $length > 1) { |
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throw new \InvalidArgumentException(sprintf('Invalid string length: %f', $length)); |
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} |
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// @todo validate against string width |
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} |
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/** |
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* Convert a number of cents to a string length. |
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* |
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* @param float $cents The number of cents between the open string and the |
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* stopped pitch. |
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* |
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* @return float The length of the vibrating string, as a fraction of the |
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* whole string's length. |
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*/ |
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private function centsToStringLength(float $cents): float |
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{ |
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return 1 / pow(2, $cents / 1200); |
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} |
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} |
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extended-strings /
strings
