illustrated directionality

[afl...@gmail.com]

hello,

side question: what microphones/sound cards do people use with baudline?

i had an idea to try mounting two identical microphones at right
angle, then subtracting left from right with channel mapping in order
to get a nice, colorful illustration of direction. my microphone input
is monaural. an immediate idea was to try two same-model sound cards,
but i am worried that production specifications might leave them out
of phase, and likely several hertz off. would that be correctable with
calibratesr? i thought of feeding left and right television audio into
both, and using deep zoom into 15734 to get both aligned in relative
frequency (at the current temperature, at least.)

i wanted to know if this was plausible before anything was bought.

[blip]

Here is a list of the sound cards I use with baudline:

http://www.baudline.com/solutions/full_duplex/


My advice is to use the "line" input channel of a single sound card with two identical microphones.  The mics will have to be self powered or you will need an external preamp.  Recording from two sound cards will create synchronization problems.  The two sound cards will either have different time zero (first buffer) offsets and/or the sampling rates will be slightly different. Unequal sample rates will cause signal drift over time.  You can measure the sample rates of two sound cards by recording two /dev/audio's and watch the rate estimates in baudline's Input Devices window.  You can even use the -debugrate option and plot the sample rate estimates.  For more sample rate information see:

http://www.baudline.com/solutions/sample_rate

The -calibratesr command line option is like the calibrate button in the Input Devices window.  Unfortunately the concept of sample rate calibration only makes sense for a single /dev/audio device.  Multiple /dev/audio sample rate calibration is a very different and complicated problem.  Maybe in the future.

Since you want to track directional information you might want to try the dual channel CrossCorrelation transform.  It will generate a spike at the time lag difference between two channels.  For information on the Crosscorrelation transform see:

http://www.baudline.com/manual/channel_mapping.html#transform

you can also make CrossCorrelation the default transform by using the following command line option:

baudline -transform crosscorrelation