Silence Detection (Michael's way)

[Albert H]

One of our number (Michael) came up with a slightly different way of doing silence detection. It's based around a 4060 CMOS Oscillator and counter IC. Incoming audio is rectified, and used to switch a transistor to toggle the reset pin on the 4060 when audio is present, so that the counter can't count up to its trigger number. If there's a long enough period of silence, the 4060 counts up until the Q13 pin goes high. This triggers a monostable that switches a relay. The relay contacts can be used to light an alarm lamp, sound a bell or buzzer, or even trigger a reset of a computer.

The audio inputs of the circuit are balanced, and it's equipped with paralleled audio sockets to allow easy connection to the output of a mixer or any other convenient point in the audio chain.

There are three LEDs on the prototype - an orange LED for "audio present" that blinks with audio, a green LED for "OK" and a red LED for "Alarming". The LEDs allow silent testing before putting the unit into service.

The silence period detected is adjustable by varying the frequency of the 4060's internal oscillator. The alarm period is adjustable too, so that the bell can ring for long enough to wake up a sleepy DJ! The audio sensitivity is aimed at ordinary line levels, but changing the values of the feedback resistors around the input op-amps can be used to adjust to suit your studio levels. There are two jumpers at the outputs of the audio rectifiers on our prototype for testing purposes (to allow testing with live programmes going out!).

It's simple enough, and has been successfully used for a while at a friend's station.

Silence Alarm V3.png

[radium98]

thank you , merry christmas everyone