![]() But once again 22-61K lacks a needed series R. Then after the two bits about the CAPS behavior at low and high frequencies, we jump to a full-on two-CAPS resonator in 22-61J, followed by an equivalent circuit in 22-61K that should be captioned "Equivalent circuit of J". And no formula is given for what the equivalent L value is.* In fact the inductance has an equivalent series R of about 1/2 the bootstrap R. But the next circuit 22-61G is incorrect as representing an inductor with no series resistance. 22-61F shows inductor synthesis with the follower-buffered CAPS network: "Bootstrap/feedback inductive synthesis using CAPS network". And that's where some of the more serious errors come into play. There are some problems there as well (for example paragraph 6 of 22.10.11, where in the penultimate sentence the word "not" should be removed).Īfter the discussion about the CAPS network, parts of Figure 22-61 are pretty much unsupported by the text. The various lettered subsections of the figure are discussed in the text. On page 756, Figure 22-61, "Inductive Reactance Synthesis", we are actually shown a step-by-step approach to the series L-C resonator needed for typical EQ boost-cut topologies. Moreover he may have been the victim of some hasty typesetting and editorial screwups (the overall book has plenty, like that bogus formula for attentuators that came up in here a while ago). I should quickly add that I love the overall piece and have great respect for Steve. I don't have time to work it out at the moment, but I got as far as to revisit some of the errors in the HSE** article. And the benefit of feedback integrators is small common-mode swing, which you lose with the CAPS configuration. In that case the current needed is only the magnitude of the input current to the integrator plus whatever the external load current is-it's not like the amplifier is driving a big C to ground and trying to produce a step function. You do however have the contribution of thermal noise from each pot.Īctually, feedback integrators don't scare me that much-I think some of Steve's objections are a bit exaggerated, particularly the peak current requirement one. You do have the advantage that the noise in the synthetic LCs nulls out at the midpoint of the boost-cut potentiometers. Whether it has any advantages or not compared to the state-variable general biquad remains to be seen.įorssell argues convincingly for the single sum-difference stage with multiple shunt L-C-R, rather than a long chain of stages. ![]() I finally got an allpass boost-cut arrangement that differs from the shunt synthetic L-C approach above. article on consoles, but not discussed to the point of showing a CAPS equivalent to a state-variable filter that actually works, I played around for a while. By the way, in the attempt to realize some of the supposed benefits of using CAPS (constant amplitude phase shift) networks deployed as filter elements, as touted by Dove in his massive HB for Sound Engineers 1st Ed.
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