# Audio level meter

#### Lonners

Joined Dec 9, 2007
3
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 http://img212.imageshack.us/img212/5640/audiolevelmeteryv8.png

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

#### bloguetronica

Joined Apr 27, 2007
1,453
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.