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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Crest factor ： ウィキペディア英語版 Crest factor Crest factor is a measure of a waveform, such as alternating current or sound, showing the ratio of peak values to the effective value. In other words, crest factor indicates how extreme the peaks are in a waveform. Crest factor 1 indicates no peaks, such as direct current. Higher crest factors indicate peaks, for example sound waves tend to have high crest factors. Crest factor is the peak amplitude of the waveform divided by the RMS value of the waveform: :$$ C = }. The peak-to-average power ratio (PAPR) is the peak amplitude squared (giving the peak ''power'') divided by the RMS value squared (giving the average ''power''). It is the square of the crest factor: :$$ \mathit = ^2 \over = C^2. :$$ \mathit_ = 10 \log_^2 \over = C^2_. When expressed in decibels, crest factor and PAPR are equivalent, due to the way decibels are calculated for power ratios vs amplitude ratios. Crest factor and PAPR are therefore dimensionless quantities. While the crest factor is defined as a positive real number, in commercial products it is also commonly stated as the ratio of two whole numbers, e.g., 2:1. The PAPR is most used in signal processing applications. As it is a power ratio, it is normally expressed in decibels (dB). The crest factor of the test signal is a fairly important issue in loudspeaker testing standards; in this context it is usually expressed in dB.〔(JBL Speaker Power Requirements ), which is applying the IEC standard 268-5, itself more recently renamed to 60268-5〕〔AES2-2012 standard, Annex B (Informative) Crest Factor, pp. 17-20 in the 2013-02-11 printing〕〔"Dr. Pro-Audio", (Power handling ), summarizes the various speaker standards〕 The minimum possible crest factor is 1, 1:1 or 0 dB. == Examples == This table provides values for some normalized waveforms. All peak magnitudes have been normalized to 1. \approx 1.414 || 3.01 dB |- | N superimposed sine waves (same amplitudes, different frequencies) || || $\backslash sqrt\}$ || $\backslash sqrt$ || $10\backslash log\; 2N$ dB |- | Full-wave rectified sine || || $\backslash approx\; 1.414$ || 3.01 dB |- | Half-wave rectified sine || || $\backslash approx\; 0.5$〔 || $2\; \backslash ,$ || 6.02 dB |- | Triangle wave || || $\backslash approx\; 1.732$ || 4.77 dB |- | Square wave || || 1 || 1 || 0 dB |- | PWM-Signal V(t) $\backslash ge$ 0.0 V|| || $\backslash sqrt$〔 || $\backslash sqrt$ dB |- | QPSK || || 1 || 1 || 0 dB |- | 8PSK || || || || 3.3 dB〔http://www.readbag.com/ece-ucsb-yuegroup-teaching-ece594bb-lectures-steer-rf-chapter1〕 |- | π/4DQPSK || || || || 3.0 dB〔 |- | OQPSK || || || || 3.3 dB〔 |- | 8VSB || || || || 6.5–8.1 dB〔http://broadcastengineering.com/mag/broadcasting_transitioning_transmitters_cofdm/〕 |- | 64QAM || || $\backslash sqrt\; \}$ || $\backslash sqrt\; \}\; \backslash approx\; 1.542$ || 3.7 dB〔 |- | $\backslash infty$-QAM || || $\backslash approx\; 1.732$ || 4.8 dB〔 |- | WCDMA downlink carrier || || || || 10.6 dB |- | OFDM || || || || ~12 dB |- | GMSK || || 1 || 1 || 0 dB |- | Gaussian noise || || $\backslash sigma$〔(Op Amp Noise Theory and Applications ) - 10.2.1 rms versus P-P Noise〕〔(Chapter 1 First-Order Low-Pass Filtered Noise ) - "The standard deviation of a Gaussian noise voltage is the root-mean-square or rms value of the voltage."〕 || $\backslash infty$〔(Noise: Frequently Asked Questions ) - "Noise theoretically has an unbounded distribution so that it should have an infinite crest factor"〕〔Telecommunications Measurements, Analysis, and Instrumentation, Kamilo Feher, section 7.2.3 Finite Crest Factor Noise〕 || $\backslash infty$ dB |} Notes: 1. crest factors specified for QPSK, QAM, WCDMA are typical factors needed for reliable communication, not the theoretical crest factors which can be larger. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crest factor」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.