Audio level meter

Discussion in 'Homework Help' started by Lonners, Dec 9, 2007.

  1. Lonners

    Thread Starter New Member

    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?
  2. cumesoftware

    Senior Member

    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.