SH lighting is verylowfrequency. You can't have sharp lighting transitions with SH lights. They are also only affecting the diffuse lighting (too low frequency for specular highlights).
In audio, a verylowfrequency oscillation often resulting from a positive feedback path in an amplifier system.
在音响设备中出现的振荡频率极低的低频振荡，常因放大系统的正反馈回路引起。
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This paper deals with a digital speech communicator of verylowfrequency and low bit digital communication based on software ratio, which USES the technique of QPSK and FEC coding.