Sound file and voltage on audio line.

Discussion in 'Room Set Up, Audio Theory, and Measurements' started by roineust, Apr 18, 2015.

  1. Hello there audio pro and mavin people!

    I have this primitive hobby project, where an Arduino micro-controller board communicates with a Smartphone, via the phone audio jack. The phone plays these Audio files and the Arduino samples the voltage on the audio line, in order to discern between high voltage, low voltage and no voltage. It's a simple project and it already works OK without any amplification and that is how i want it to stay, for this project (without amplification).

    But i have a suspicion that it could work even better, if i had a bit more knowledge about the types of sounds, that produce various levels of voltage on an audio line. What i am using now is a sound of a siren, that i recorded with such a gain, that it is full of distortion. i think distortion is good for my case, since it seems to be decoded by the Arduino, as a high voltage signal most of the time. But when i installed a primitive sound editor software on my computer and set the graphic view of the sound file in a certain way, i saw that actually only small portions of that sound file, raises the sound magnitude to the maximum possible gain. My conclusion was that it must be surly possible to create a sound file, that produces even a higher constant voltage on the audio line. The sound file runs for 5-10 seconds.

    So my question is what kind of sound sample would produce the highest voltage on an audio line?

  2. I'm not some kind of expert, but I think we need more detail. The peak voltage out of the headphone jack is set by the controller in the phone or the hardware itself (I don't know those details and they will vary from device to device slightly - unless you are hacking the phone this is fixed). The question is how to engineer a signal which meets your needs. A digital signal out of a tone generator (I'm sure you can find free PC software for this) could probably be specified however you want. Regardless of the acoustical sound of the signal, you could specify the maximum signal level you want and have the phone play it back and get the peak voltage the hardware/software can deliver.

    But that's PEAK. I have a hunch that what you are looking to maximize is RMS or some other type of average voltage. For that, pure tone sine waves will produce the highest RMS voltage for any given peak voltage. You should see an RMS value that is -3dB from the peak voltage in that case.

    Maybe that helps?


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