A hearing assistive device including an audio processing circuit comprising: - a delta sigma analog-to-digital converter having ∘ an analog input being an audio signal; ∘ an integrator connected to integrate a voltage present in a summation point that is coupled with the input signal; ∘ a comparator connected to compare a voltage output from the integrator with a reference voltage (V ref) and outputting a logic level in accordance with the comparison; ∘ a flip-flop connected to latch the comparator output; ∘ a feedback loop coupling a feedback signal back to the summation point; and the feedback loop comprises a DA-Converter using the latched comparator output to generate the a feedback signal; and - a power supply voltage (V battery) provided by a battery showing a decay during discharging; - wherein a reference voltage generation circuit is adapted to provide the reference voltage (V ref) at a voltage level lower than that of the power supply voltage (Vbattery) and to follow the decay of the power supply voltage (Vbattery) with a predefined margin; wherein the reference voltage generation circuit comprises: - a low-pass filter circuit comprising a diode and a capacitor arranged to remove noise originating from the power supply, the capacitor connected between the diode's cathode and ground; - a first voltage divider (R1, R2), connected between the power supply voltage (Vbattery) and ground, wherein the output from the first voltage divider (R1, R2) is connected to the diode's anode; - an electronic voltage amplifier (op-amp) to output the reference voltage (Vref) and with a first input connected to the diode's cathode; and - a second voltage divider (R3, R4) connected between the reference voltage (Vref) and ground, wherein the output from the second voltage divider (R3, R4) is connected to a second input terminal of the electronic voltage amplifier (op-amp). - a delta sigma analog-to-digital converter having ∘ an analog input being an audio signal; ∘ an integrator connected to integrate a voltage present in a summation point that is coupled with the input signal; ∘ a comparator connected to compare a voltage output from the integrator with a reference voltage (V ref) and outputting a logic level in accordance with the comparison; ∘ a flip-flop connected to latch the comparator output; ∘ a feedback loop coupling a feedback signal back to the summation point; and the feedback loop comprises a DA-Converter using the latched comparator output to generate the a feedback signal; and ∘ an analog input being an audio signal; ∘ an integrator connected to integrate a voltage present in a summation point that is coupled with the input signal; ∘ a comparator connected to compare a voltage output from the integrator with a reference voltage (V ref) and outputting a logic level in accordance with the comparison; ∘ a flip-flop connected to latch the comparator output; ∘ a feedback loop coupling a feedback signal back to the summation point; and the feedback loop comprises a DA-Converter using the latched comparator output to generate the a feedback signal; and - a power supply voltage (V battery) provided by a battery showing a decay during discharging; - wherein a reference voltage generation circuit is adapted to provide the reference voltage (V ref) at a voltage level lower than that of the power supply voltage (Vbattery) and to follow the decay of the power supply voltage (Vbattery) with a predefined margin; - a low-pass filter circuit comprising a diode and a capacitor arranged to remove noise originating from the power supply, the capacitor connected between the diode's cathode and ground; - a first voltage divider (R1, R2), connected between the power supply voltage (Vbattery) and ground, wherein the output from the first voltage divider (R1, R2) is connected to the diode's anode; - an electronic voltage amplifier (op-amp) to output the reference voltage (Vref) and with a first input connected to the diode's cathode; and - a second voltage divider (R3, R4) connected between the reference voltage (Vref) and ground, wherein the output from the second voltage divider (R3, R4) is connected to a second input terminal of the electronic voltage amplifier (op-amp).