constantly record and analyze microphone input

[chip007]

Is it possible to analyze microphone input data while it is being recorded? My program needs to measure the input voltage and the program needs to procede when the voltage is equal to 5V.

Thank  you.

[Conseils]

Absolutely, go and search through the examples using the keyword SOUND
 (I am sort of assuming that you are using a sound card here) all the principles apply though even if its an analogue input on a DAQ card.

[chip007]

I think I found a sound example that analyzes the sound while it is acquired ("Sound Card AutoPower Spectrum"). What units is the sound data acquired in and how can I change it just to simple volts?

[chip007]

and yes, i am trying to use the sound card to get the data

[Conseils]

The sound card can be a bit problematic in this sense especially if you change the input gain for the mic and watch out for any bass boost function being on used as this will affect the scale as well.

As for the scaling on a standard sound card, there is none as such (see article 3 below). The input is represented as ±32767 on a standard 16 bit card and obviously larger for the newer 24bit cards.

The easiest option would be to generate a signal, measure it and then play into the mic input. I would suggest that the mic input (or possibly better the line input) would be in the order of a couple of hundred milli volts so if youre sure that you have a five volt signal then you will need to scale the input with a resistor (say a 5K ohm variable resistor set up as a potential divider).

You may find that the following articles will help not only with the principles but with the practice as well: -
http://www.virtins.com/Virtins_Sound_Card_Oscilloscope_Probe_Manual.pdf
http://www.techmind.org/audio/

This link is quite good as well:-
http://www.audioprecision.com/index.php?page=support&id=1100001014

If its a mac the following may apply (I don;t use them a great deal, sorry): -
http://www.channld.com/distspec.html

[Justin D]

chip007,

I don't believe that there's any way to convert what's being read from the soundcard into a voltage directly.  The soundcard doesn't really care what the absolute voltage of a signal is, just the relative changes in voltage.  A better way to do what you're trying to do would be to watch the output of the sound card and see what level it gets to when you want your program to procede.  Then you can just watch for this level.  Also, in all of the microphones that I've dealt with I've never heard of one that could get up to 5V amplitude.  Usually microphones generate a very small voltage.  5V might be a little high of a threshold to look for.

Hope this helps,
Justin D.
Applications Engineer
National Instruments