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Programme level refers to the signal level that an audio source is transmitted or recorded at, and is important in audio if listeners of Compact Discs (CDs), radio and television are to get the best experience, without excessive noise in quiet periods or distortion of loud sounds. Programme level is often measured using a peak programme meter or a VU meter. The level of an audio signal is among the most basic of measurements, and yet widespread misunderstanding and disagreement about programme levels has become arguably the greatest single obstacle to high quality sound reproduction. == How it works == Live sound covers an enormous range of levels, but this is not something that can be demonstrated with a conventional sound level meter. Sound level meters respond quite slowly, even on a "fast" setting: they use a root mean square (RMS) rectifier which by definition must take a slow running average of the square of the input voltage. Music is complex, and constantly varying, with brief peaks originating from many sources including the initial impact of sticks on cymbals and drums. A loud band might measure 100 dB SPL on a sound level meter, yet have peaks reaching 130 dB SPL or higher. A recording system must handle these peaks; they can be measured using a peak responding meter with an integration time of 0.5 ms or less (not a standard IEC type PPM which has a longer integration time). The sound level meter is useless for properly assessing noise levels, since the commonly used A-weighting is based on equal-loudness contours for pure tones, and is not valid for the random noise. The subjective loudness of noise is best measured using a noise-meter to the ITU-R 468 noise weighting standard. The chart below shows, on this basis, the real range of live music, and then the level capabilities of various stages in the audio chain, from microphone to loudspeaker. 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「Programme level」の詳細全文を読む スポンサード リンク
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