[LAD] Audio Trigger

OrazioPirataDelloSpazio (Lorenzo) ziducaixao at autistici.org
Sat Nov 8 16:19:09 UTC 2008

Hello Gene and thank you for your response.
Gene Heskett ha scritto:
> On Thursday 06 November 2008, OrazioPirataDelloSpazio (Lorenzo) wrote:
>> Hi all,
>> I need to use a microphone input as a trigger. In other words my idea is
>> to connect a switch to the microphone input. In this way, when the
>> switch is turned on it generates a spike in the captured track.
>> I would like to create a program that trigger an event every spike it
>> receives.
> 1st, the switch needs to switch a voltage, otherwise there is nothing to 
> record.  
I was thinking the same but even if the switch always open produces no 
signal, and the always closed produces no signal, when the switch is 
closing it does produce a signal!
Here you can find two wave files: 
trig.wav -> caputed when I trigger the switch
notrig.wav -> the switch is always open

As you can see there is some spikes in the first. If I open with 
audacity, I can see the volume level that raise when I closed the switch 
(about 5 or 6 times in the wav file).

So I cast every couple of bytes in a int16_t as you suggest, and make 
the program trigger after a given threshold is overwhelmed.

So I write a simple program that when the captured sample overwhelm a 
given threshold, it triggers. The code is here:

When I fix the treshold to 180, it does work properly, even if sometimes 
it exchange a "white noise" sample for my trigger.


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