LED vumeter circuit using LM324

This LED vumeter is built using LM324 operational amplifiers and some classic electronic components.
Inverting input of each of AO receives a reference voltage provided by voltage divider R10 *R3 (values of these resistors were chosen to get up to 5 dB between two adjacent resistors). Resistors R1 and R12 are the reference voltage is greater than half the supply voltage.
Noninverting input of each AO receives input rectifier (D1 and D2) and superimposed mid-supply voltage.
When the voltage on the positive input of an inverting input exceeds the AO, AO pass out in "H" and its associated LED lights. The higher the input signal, the more it will turn more LEDs. If D3 and D4 are red, the circuit can be used as a simple leading indicator, indicating a level exceeded by the input signal.
Power can be between 10 V and 15 V, input current depends on the number of LEDs lit.