线性相位非均匀带宽DFT调制滤波器组设计

Design of linear phase non-uniform bandwidth DFT modulated filter bank

提出了一种非均匀带宽DFT调制滤波器组设计方法,该方法在设计近似重构、过采样均匀DFT调制滤波器组的基础上,用全通滤波器代替其多相结构中的延迟单元,在不改变原滤波器组系数的条件下获得非均匀的频带划分;针对这种变换带来的信号重建相位失真问题,在滤波器组输出端构造一个相位补偿器,并采用最小二乘法设计,使得设计出来的FIR补偿滤波器在全频带范围内直接逼近理想补偿器的频率响应。与现有的补偿方法相比,该方法具有更小的幅度和相位近似误差,并且有效地降低了补偿滤波器的阶数。通过对全通变换参数的合理选择,可以使非均匀频带分布满足符合人耳听觉特性的Bark域,从而适用于语音信号处理。

This paper proposes the design method of non-uniform bandwidth DFT modulated filter bank. Based on de- signing the approximate reconstruction,oversampling uniform DFT filter bank, we replace the delay units with allpass filters in the polyphase structure, which maps the linear frequency to the warped frequency without changing the filter bank coefficients. Aiming at the signal reconstruction phase distortion problem caused by the allpass filter transfomm- tion, we propose a method that compensates the nonlinear phase response using a phase equalizer at the end of the fil- ter bank. Least square technique is adopted to design the FIR equalizer, which is aimed to approximate the ideal phase equalizer within the entire frequency band. Compared with existing compensation methods, the proposed ap- proach has lower amplitude and phase approximation errors, and reduces the filter order effectively. Reasonably selec- ting the allpass transformation parameters can make the non-uniform frequency band distribution coincide with the Bark scale of human auditory system, which is suitable for speech signal processing.