/** * * @param type $compre * @return type */ public static function heavyCompression($compre) { // The first four bits indicate gain changes in 6.02dB increments which can be // implemented with an arithmetic shift operation. The following four bits // indicate linear gain changes, and require a 5-bit multiply. // We will represent the two 4-bit fields of compr as follows: // X0 X1 X2 X3 . Y4 Y5 Y6 Y7 // The meaning of the X values is most simply described by considering X to represent a 4-bit // signed integer with values from –8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The // following table shows this in detail. // Meaning of 4 msb of compr // 7 +48.16 dB // 6 +42.14 dB // 5 +36.12 dB // 4 +30.10 dB // 3 +24.08 dB // 2 +18.06 dB // 1 +12.04 dB // 0 +6.02 dB // -1 0 dB // -2 –6.02 dB // -3 –12.04 dB // -4 –18.06 dB // -5 –24.08 dB // -6 –30.10 dB // -7 –36.12 dB // -8 –42.14 dB $fourbit = str_pad(decbin(($compre & 0xf0) >> 4), 4, '0', STR_PAD_LEFT); if ($fourbit[0] == '1') { $log_gain = -8 + bindec(substr($fourbit, 1)); } else { $log_gain = bindec(substr($fourbit, 1)); } $log_gain = ($log_gain + 1) * GetId3_Lib_Helper::RGADamplitude2dB(2); // The value of Y is a linear representation of a gain change of up to –6 dB. Y is considered to // be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can // represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain // changes from –0.28 dB to –6.02 dB. $lin_gain = (16 + ($compre & 0xf)) / 32; // The combination of X and Y values allows compr to indicate gain changes from // 48.16 – 0.28 = +47.89 dB, to // –42.14 – 6.02 = –48.16 dB. return $log_gain - $lin_gain; }
/** * * @return boolean */ public function CalculateReplayGain() { if (isset($this->info['replay_gain'])) { if (!isset($this->info['replay_gain']['reference_volume'])) { $this->info['replay_gain']['reference_volume'] = (double) 89.0; } if (isset($this->info['replay_gain']['track']['adjustment'])) { $this->info['replay_gain']['track']['volume'] = $this->info['replay_gain']['reference_volume'] - $this->info['replay_gain']['track']['adjustment']; } if (isset($this->info['replay_gain']['album']['adjustment'])) { $this->info['replay_gain']['album']['volume'] = $this->info['replay_gain']['reference_volume'] - $this->info['replay_gain']['album']['adjustment']; } if (isset($this->info['replay_gain']['track']['peak'])) { $this->info['replay_gain']['track']['max_noclip_gain'] = 0 - GetId3_Lib_Helper::RGADamplitude2dB($this->info['replay_gain']['track']['peak']); } if (isset($this->info['replay_gain']['album']['peak'])) { $this->info['replay_gain']['album']['max_noclip_gain'] = 0 - GetId3_Lib_Helper::RGADamplitude2dB($this->info['replay_gain']['album']['peak']); } } return true; }