Yamaha PM4000 Owner's Manual (image) - Page 111
There is one further distinction between VCA groups
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trolled Amplifier) in the input module. The audio signal flowing through that VCA is, in turn, increased or decreased in level according to the control voltage applied to the VCA. One advantage of the VCA is that the control voltage applied to it can come from more than one point. In fact, when one or more of the input channel's VCA ASSIGN switches [22] is engaged, control voltage from the correspondingly numbered VCA Master Faders [47] is also applied to the channel VCA The circuitry is such that the VCA Master will cause the assigned input channel(s) post-fader output levels to ride up and down, scaled to the channel Fader setting. Of course, the channel(s) output signal must still be assigned somewhere. NOTE: It may not be obvious, but VCA master faders and VCA assign switches have nothing at all to do with where the audio signal goes. They only affect its level. The signal must be assigned via bus assign switches, and/or Aux Send controls. If the signal on several channels is assigned directly to the stereo bus using the channels' ST assign switch [3], then the VCA Master to which those channels are assigned will act like a Group-to-Stereo fader. If the channels' output is assigned to a Group bus using a Group assign switches [1], then the VCA Master [47] to which those channels are assigned will control the level applied to the Group Master [42], which is somewhat redundant but does serve some useful purposes. What cannot be done with a Group Master Fader [42] that can be done with a VCA Master [47] is controlling the post-fader AUX SEND levels from groups of input channels. While it's true that the Aux Send Master LEVEL controls [38] affect the overall bus output level on the eight aux busses, each of these busses can be considered a discrete output. Of the many input channel AUX SEND controls that may be feeding a given Aux Send Master LEVEL control, some can be controlled by one VCA Master, and others by another VCA Master. Thus, when "subgrouping" is accomplished with the VCA Master Faders, the output of affected input channels is controlled more completely. That is, the channels' Group, Stereo, and Post-Fader Aux Send outputs are all affected by the assigned VCA Master(s). What cannot be done with a VCA Master Fader [47] that can be done with a Group Master Fader [42] is the processing of a single, mixed signal. Consider, for example, that a given group of signals must be compressed... say the backup vocal mics. If the several input channels which accommodate backup vocals are all assigned to a single Group Master Fader, then one compressor/limiter can be inserted in the Group INSERT IN/OUT patch point [118], affecting the mixed signal on that group mixing bus. On the other hand, if those same input channels were instead controlled as a "group" by a VCA Master Fader, and the channel outputs were assigned to various group mixing busses, then it would be impossible to compress the backup vocal mix. Instead, multiple compressor/limiters would have to be inserted in the individual channel INSERT IN/OUT patch points [102]. The latter approach is more costly, and also applies the effect to all the channel's outputs, rather than just to a specific group. VCA Master Fader grouping is often useful for control of scenes, songs or sets, whereas conventional Group Master Faders are often useful for control of related groups of mics and instruments. For example, one VCA Master might be assigned to control all drum microphones. Another VCA Master might also be assigned to the same drum microphones, plus any percussion and guitar mics. One VCA Master would then affect drum levels, while the other would affect the entire rhythm section. In some cases, multiple channels that are assigned direct to the stereo bus can be controlled in groups by the VCA Masters, while other channels can be assigned to different Group Master Faders, and the Group Masters, in turn, can be assigned to stereo; using this approach, one has the equivalent of 16 groups mixed to stereo. There is one further distinction between VCA groups and conventional groups. If one were to use conventional groups to control scenes, sets or songs, a given input channel might well be assigned to several group mixing busses. The mix matrix would then be used to combine those busses, with the group master faders serving as scene controllers. If, in this instance, two Group Master Faders were raised to nominal position, and the same input channel was assigned to both of those groups, that channel's level would rise 3 dB in the combined matrix output, throwing it out of balance with other single-assigned channels. This is because that channel signal is being added together twice in the matrix. If instead of using conventional Group Master Faders, VCA Master Faders were used to control the scenes, and one input was assigned to two (or more) VCA Masters, the above level "build up" would not occur, and the correct balance would be retained. That's because when VCA Master Faders are set to nominal position, they output zero volts... which means they don't change the level coming from the input channel. Whether one, two or all eight VCA Master Faders are assigned to a given input channel, the channel's output level will not change so long as the VCA Masters are at nominal. Page 7-5