Frequency filtering with sound card input

Question

I created a VI that filtered a particular input at the desired
frequencies (I have attached it incase you are interested, but its not
necessary to answer my question).  However, when I replaced my
testing signal (express vi) with the soundcard input, it no longer
filtered.  I think this is becuase my filters require dynamic data
type input and the soundcard doesnt output that, thus requiring me to
use a converter.  Could you please direct me to more information
about the "dynamic data" type?  As well as offer any solutions or
insight into filtering in the frequency domain with input from a
soundcard.  Thanks.
Attachments:
v2.vi ‏806 KB

Answer 1

Hi Elen,
The Dynamic Data type (DDT) can hold many different types of data. When
you use the "Convert to Dynamic Data" Express VI, you can configure
exactly how you want to interpret your data. In your case, you are
converting the array to a "1D array of scalars - single channel". This
basically means that you are still passing the data as an array in DDT
clothes.
The issue with your VI is that you only are passing the array of data
to the Filter Express VI. When this VI receives an array that doesn't
hold any timing information (t0 and dt) it expects that dt is 1 second.
In your case, dt is the reciprocal value of the sample rate, so you
will get wrong results if you don't specify this for the Filter Express
VI. What you have to do, is create a Waveform that includes the dt and
the array, and then pass this Waveform to the Filter VI. Here's the
easiest way to do it:
It is not necessary to specify t0 unless you need to take absolute time
into account. The above changes should be enough to make your example
work.
Have fun!Message Edited by Philip C. on 07-20-2005 09:53 PM
- Philip Courtois, Thinkbot Solutions
Attachments:
ArrayToWDT.PNG ‏7 KB