Do you have a real feel of dB?

When working with digital signal processing, sooner or later you must deal with filters. Design a digital filter is an easy matter. Just install a filter designer, entry your design parameters and... voilà! you have your filter designed... or not.

If your specifications are kind, probably you can obtain the filter, but if your specifications are tight (or even crazy) probably is almost impossible or at least very difficult to implement.

Well... now you are facing a typical engineering problem: A compromise. A example: Designing a simple FIR digital filter, we can choose between a sharp roll-off on transition band or a strong attenuation on the stop-band for the same pass-band characteristics and number of taps. Are enough 35dB of attenuation? Should I sacrifice roll-off to get 10 extra dB?

We don't have the answer for this questionbut this experiment can help. This experiment compares one signal with an attenuated version of itself. Two type of signals can be compared: An internally generated tone and an external signal introduced through LINE-IN.

The result can be listened from LINE-OUT or HP-OUT on the same kit. Experiment shows attenuations of 3, 6, 10, 20, 30, 40, 50, 60 and 70 dB.

Runs on EVKIT for OMAPL137 under CCSv4 and the whole code with extra explanations can be obtained from: http://sites.google.com/site/dspradiol137/downloads/100101a.zip