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LOW_PASS_FILTER_PHASE_CORRECTOR

2017-02-26 18:58  
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LOW_PASS_FILTER_PHASE_CORRECTOR
In some applications, it might be desired, or even be essential, that the bandwidth of the audio signal be limited, but that the phase relationship with the original signal be retained. A surroundsound encoder is a good example of this. The requirement can be met by combining the low-pass filter with an all-pass section and having the filtered signal compared with the signal corrected by the all-pass network. As it happens, the phase transfer of a first-order all-pass filter is exactly the same as that of a second-order critically damped network. The design of such a combination is shown in Figure 1. In this, the all-pass network is based on IC1a and the low-pass section on IC1b. The -6-dB cutoff point is at exactly 1 kHz, and the -3-dB rolloff is at 642 Hz.