Dolby Noise Reduction

Dolby 噪声降低

The Dolby systems for noise reduction employ circuitry which pre-emphasizes high frequencies before they are recorded onto tape in order to make them larger than the tape hiss noise with which they compete.

Dolby系统的降噪电路在信号被录制到磁带之前会预先增强高频成分，以便使这些高频成分的幅度大于磁带的噪声。

The circuitry is amplitude-sensitive: only soft high-frequency sounds are emphasized. If loud high-frequency sounds were emphasized, it might drive the tape into its distortion levels. Upon playback, a matched de-emphasis circuit is employed to restore the high frequencies to their proper balance with the other part of the recorded signal.

电路对幅度敏感：只有柔和的高频声音会被强调。如果强调了响亮的高频声音，可能会导致磁带进入失真范围。在播放时，会使用匹配的去强调电路来恢复高频声音在录音信号其他部分中的适当平衡。

Dolby-B encoding curves

Dolby-B 编码曲线

Index

Sound reproduction concepts

Tape recording concepts

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Dolby Systems

Dolby Systems（专名或术语）

The Dolby systems for noise reduction employ circuitry which pre-emphasizes high frequencies before they are recorded onto tape in order to make them larger than the "tape hiss" noise with which they compete.

杜比噪声抑制系统采用电路在信号被录制到磁带之前对高频进行预强调，使它们的幅度大于它们所竞争的“磁带嘶嘶声”噪声。

Dolby A Dolby A（专名或术语）	The professional level version of the Dolby process. Used in high speed multi-track machines. 专业电平版本的Dolby过程。用于高速多轨机器。
Dolby B Dolby B（专名或术语）	The most widespread version of the Dolby process, used in most popular stereo tape decks. 最普遍的Dolby过程版本，用于大多数流行立体声磁带录音机。
Dolby C Dolby C（专名或术语）	A more recent version of the Dolby process involving double compression. The resulting tapes produce more satisfactory results if played on non-Dolby units than the A and B versions. 一种更近期的Dolby过程，涉及双压缩。如果在非Dolby设备上播放，这种结果的磁带比A和B版本更令人满意。

Dolby-B encoding curves

Dolby-B 编码曲线

Dolby-B encode/decode balance

杜比-B 编码/解码平衡

Index

Sound reproduction concepts

Tape recording concepts

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Dolby Recording and Playback

Dolby录音与播放

If a tape is recorded using a Dolby noise reduction system, then it should by played back with the same system. If the recording and playback systems do not match, several types of problems arise, as summarized in the table.

如果使用Dolby降噪系统录制磁带，那么在回放时应使用相同的系统。如果录制和回放系统不匹配，就会出现多种问题，如表中所总结的。

RECORD 记录	PLAYBACK 回放	RESULT 结果
Without Dolby 无杜比	Without Dolby 无杜比	Properly balanced music, but fidelity limited by tape hiss. 平衡的音乐，但保真度受磁带噪声限制。
With Dolby With Dolby（专名或术语）	Without Dolby 无杜比	High-frequencies over-emphasized upon playback 高频在播放时被过度强调
Without Dolby 无杜比	With Dolby With Dolby（专名或术语）	Dull sound from de-emphasized highs, boomy bass 暗淡的音色，低音突出
With Dolby With Dolby（专名或术语）	With Dolby With Dolby（专名或术语）	Optimum balance and fidelity. 最佳平衡与保真度

The problems discussed here are most severe in common practice with Dolby-B, which is the most common for non-professional use. The more recent Dolby-C does not produce as severe a problem when played back on non-Dolby equipment.

此处讨论的问题在使用Dolby-B时最为严重，而Dolby-B是非专业用途中最常见的。较新的Dolby-C在回放于非Dolby设备时，并不会产生同样严重的问题。

Dolby-B encode/decode symmetry

Dolby-B 编码/解码对称性

Index

Sound reproduction concepts

Tape recording concepts

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Dolby B-system Encoding

Dolby B-system Encoding（专名或术语）

In the Dolby-B system of noise reduction, low-level, high frequency signals are pre- emphasized upon recording as shown by these encoding curves. They are de- emphasized upon playback to discriminate against tape hiss.

在Dolby-B噪声削减系统中，低电平的高频信号在录音时会被预先增强，如这些编码曲线所示。在播放时，这些信号会被减弱以抑制磁带噪声。

Dolby-B encode/decode symmetry

Dolby-B 编码/解码对称性

Index

Sound reproduction concepts

Tape recording concepts

索引声学再现概念磁带录音概念

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