On Sat, Dec 11, 2010 at 1:15 PM, TheSeeker <[email protected]> wrote:
> I have been thinking if when i use the funcion AudioRecord at 8KHz by > sample I have aliasing? To avoid the effect of aliasing normally i > should put a low pass filter to eliminate frecuencies above 4KHz > So i have this filter for default? > > You can't remove aliasing after it's occurred, so if there isn't an analog anti-aliasing filter prior to sampling, you cannot remove it in the digital domain. I would expect the A/D to operate as a sample-and-hold, which would alias frequencies higher than f_s/2. The other option that could be implemented is to integrate the signal during the sample period, which has some low-pass filtering effect (boxcar filter), but it's not a very good filter. I'm not aware how the electronics work in the devices. What device(s) are you using? Maybe the 8kHz sampling is actually sampled at 44.1 kHz, and there is digital filtering/down-sampling to 8kHz. Or perhaps there are electronics that change the anti-aliasing filter as the sample rate changes. The other question is why are you sampling at 8kHz? Will you likely have frequencies above 4kHz? Patrick -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
