Abbreviation for Time Variant Amplifier, which is essentially what it sounds like: a gain stage that can change its level over time based on some control input. TVA’s commonly have several stages or points relating to a passage of time where the level can be set. For example, one stage could be set up to lower the sound level by 10 dB and allow 10 seconds to pass before moving on to the next stage, which would have its own level adjustment and timing set. This allows the user to have precise control over how a sound’s level rises and falls (otherwise known as its envelope) each time a key is played. The term TVA is often used by Roland in their synthesizers, where it replaces what is commonly known as the ADSR or envelope generator in other brands (the main functional difference is that an envelope generator can be applied to things besides amp gain). An envelope generator controlling something like a VCA is essentially what a TVA is.