How to understand V2164 VCA control voltage per dB?
Am I right that -100dB can be considered "full attenuation"?


Yes, for audio purposes, -100 dB is typically sufficient for "silence".


  Do I understand right that in order to get -100 dB attenuation I need -3.3V control voltage level?


No, you've got things backwards. You are confusing attenuation and gain: you can't get -100 dB of attenuation because that is 100 dB of gain. By "-100 dB attenuation", you actually mean 100 dB of attenuation which is equivalent to -100 dB of gain. Higher gain means louder, higher attenuation means quieter.

If the slope of the VCA is –33 mV/dB and you want -100 dB of gain (100 dB of attenuation), then you need (-100 dB)*(-33 mV/dB) = 3.3 V. See the reference schematics, they show the control voltage port being fed by a positive voltage via a potentiometer.


  Why is there a minus sign in the "-33mV/dB"?


Because that's the way they designed the chip: if 0V = 0dB, a positive slope in mV/dB would be inconvenient.

One final note about the SSM2164 and clones: take a look at Fig. 21: Gain Constant vs. Temperature. If you're hoping for a stable gain over a wide temperature range, this may not be the best choice: the gain constant isn't very constant...