It overcame the shortcoming of the hardthreshold function's discontinuousness and improves the constant error.
该阈值函数既克服了硬阈值函数不连续的缺点,又修正了软阈值函数存在的恒定偏差。
英语百科
Observational error
Observational error (or measurement error) is the difference between a measured value of quantity and its true value. In statistics, an error is not a "mistake". Variability is an inherent part of things being measured and of the measurement process.