| 摘要 |
A system and method for reducing switching noise generated when an audio signal envelope is abruptly changed provides for gradual change of the audio signal envelope from one level to another. This gradual change over time in the audio signal envelope can be either near-linear or logarithmic. The system has a volume control register for storing a digital value representative of the envelope magnitude, an up/down counter initialized to a predetermined value, a comparator for comparing the contents of the volume control register and the up/down counter, and a digital-to-analog converter (D/A) which produces the audio signal envelope. The up/down counter output forms the input to the D/A. If the value of the volume control register is larger than the value of the up/down counter then the counter counts up until the values are equal. If the value of the volume control register is smaller than the value of the up/down counter then the counter counts down until the values are equal. If the value of the volume control register is equal to the value of the up/down counter then the counter maintains its state. The clock signal input to the counter is varied so that the user may select between a near-linear change in the D/A output envelope or a logarithmic change.
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