Audio level meter

Thread Starter


Joined Dec 9, 2007
I'm having some major trouble understanding how to do this task.

I have to design a peak level display system
input impedance 47kΩ
hold time 12dB/s
capable of displaying audio levels of -3dBu, 0dBu and +3dBu
accuracy of ±0.2dBu
display capable of bar and spot functions
(TTL logic devices required for spot display)

I have a block diagram

Please could someone show and explain the steps of how to do this?


Joined Apr 27, 2007
The diagram is straight forward. You have to use three comparators. To establish Vref, you can use a resistive network as a voltage divider (three resistors in series), connected to a constant voltage source (a zener will do). If you can't find the appropriate zener, use a fourth resistor in series with the other three ones. About the peak level holder I assume it is a device to hold the peak voltage for some time. Perhaps a small capacitor in parallel between the input signal and ground will do.

To determine decibels:
dB = 20 x log (Vm / Vref), being Vref the reference voltage for 0dB and Vm the measured voltage.

For the capacitor use the charge time relationship:
T = ln (1 / (1 - (V / Vt)))

I think that is pretty much it.