Dears,
Hi, I"m new to arduino.I wish to make a Silence Detector. A digital Audio signal is using as input.
when no audio signal for a defined period of time, turns on a buzzer alarm in that time.
Please guide
Thanks in advance
I do not think the forum can guide you with so little background information.
There are many formats of digital audio. Many of them will be beyond the capabilities of most Arduino to receive.
As mentioned above, the first thing you need to do is identify and decode the digital audio stream.
Only then can you look for characteristics i of the program (silence, phase, over level etc).
So the buzzer is going to be picked up by your microphone and then ruin the silence. So that turns off the buzzer and it becomes silent (what ever your definition of silence is). This is called a feedback loop.
Note there is no such thing as silence, only a noise under the threshold you define as silence.
Did you selected a Sound Sensor and developed a schematic? Show us your efforts
If only there was a way to solve a problem like this. Maybe having a microprocessor in the loop would help, IDK.
a7
Welcome. Use the internet to find your desired information. Gather your hardware. Create your program. If you have questions, post them here.
(hint: detecting sound is the opposite of detecting silence.)
Only with acoustic souncd 
Not if it's a digital (or other electronic) signal.
And you CAN have digital silence, which is a series of zero-value samples, or no signal at all. A WAV file full of zeros has a level of minus infinity dB. But that generally means no conversion from analog.
That is only
...meanwhile Op is keeping silence...