In this digital volume control circuit, the IC1 timer 555 is set up as an astable flip-flop to deliver low-frequency pulses to up/down clock input pins of pre-setable up/down counter 74LS193 (IC2) through push-to-on switches S1 and S2. To adjust the pulse width of pulses from IC1, you may possibly replace the timing resistor R1 by using a variable resistor.