ejektor, electronically variable resistance

For control of signal levels, particularly in low-frequency circuits, some kind of elec-tronically variable resistance is often required. In the past, LDRs have been used in conjunction with LEDs or filament lamps; FETs or even bipolar transistors have been tried with varying success; one might even consider using a thermistor with some form of heating element. What these and similar approaches lack in sophistication they make up for in associated problems: distortion, noise, non-linearity, etc. Notto mention the difficulties involved in ensuring reasonable tracking between several units. However, the alternative proposed here seems quite promising.