Lets see....a sample time of 50ms is a rate of 20 samples/sec
which gives a nyquist frequency of 10Hz (assuming I can still
do simple arithmetic in my head, not always a good assumption).
So, your PCM data should look like garbage because the mic probably
has a freq-resp of about 0 there, but you will see a whole bunch
of aliased higher frequency samples...
Kicking the timer up to 1ms will give you about 500Hz, but trying
to get intelligible audio would require at least a order of magnitude
higher freq response, circa 5KHz, or .1ms/sample. To do that rate you
need to look at the microsecond timers or free run the ADC with the
right pre-scaler. And there may still be problems with HF aliasing
because there is no low-pass filter on the mic.
Then, err, what do you do with the data? Micaz's can send around 3Kb/s
with GenericComm wide open...
Anyway, people keep trying to do this and I keep sending them to
the HighFrequencySampling demo app. Then I hear that it doesn't work
very well. Unfortunately this is just about all I know on the subject.
Perhaps a little help-list search will turn up investigators who have
gotten this to work.
MS
antonio gonga wrote:
Hello,
I'm using MicC component to acquire audio from Microphone in MicaZ Motes,
Anyone knows what´s the correct Timer rate may I use(sample period)? At
this time I'm using 50ms.
Timer.start(TIMER_REPEAT,50);
event result_t Timer.fired(){
call ADC.getdata()
}
|Auido Sensor| -------Via Rfm to ----->Bas Mote(connected to PC) and I
use a java application to read data from Serial port and record it to a
File, but the file that I have obtained it's not seemed to PCM.
if anyone can >Help me , please feel free to answer back to me
regards
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