I tried modeling the VP-330 in Pure Data. I analyzed the circuits to determine the filter frequencies. Each of the 7 bands consists of a pair of 2-pole bandpass filters in series. Each of the vocal sounds is a weighted sum of 4 different filters.
Filter1: f1 = 175 Hz, q1 = 6.79; f2 = 216 Hz, q2= 6.83
Filter2: f1 = 209 Hz, q1 = 6.79; f2 = 257 Hz, q2 = 6.83
Filter3: f1 = 559 Hz, q1 = 6.96; f2 = 671 Hz, q2 = 6.83
Filter4: f1 = 845 Hz, q1 = 7; f2 = 1007 Hz, q2 = 6.83
Filter5: f1 = 1202 Hz, q1 = 6.81; f2 = 1473 Hz, q2 = 6.83
Filter6: f1 = 2532 Hz, q1 = 6.83; f2 = 3098 Hz, q2 = 6.83
Filter7: f1 = 2974 Hz, q = 6.78; f2 = 3660 Hz, q2 = 6.83
Upper Male 8': 0.1875*Filter2 + Filter3 + Filter4 + 0.3125*Filter6
Upper Female 4': 0.1875*Filter3 + Filter4 + 0.6875*Filter5 + 0.1875*Filter7
Lower Male 8': 0.3125*Filter1 + Filter3 + Filter4 +0.3125*Filter6
Lower Male 4': 0.125*Filter2 + Filter3 + Filter4 + 0.3125*Filter6
The individual sounds are summed, so combining sounds will change the mix of the different filters.
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