Keyboard Scaling

If the keyboard pitch voltage is connected to the cut-off frequency CV (Control Voltage) input of a VCF (Voltage-Controlled Filter), then the cut-off frequency can be made to track the pitch being played on the keyboard. This means that any note played on the keyboard is subjected to the same relative filtering, since the cut-off frequency will follow the pitch being played. Also known as pitch tracking.

Source: Text (Sound Synthesis And Sampling)