resampling & anti-alias filters

[MrLip]

I've moved up from 44.1KHz sampling to 48KHz. I did searches for these questions but didn't find anything.

First, when going back down to CD format (44.1), what is the preferred method of converting down to 44.1? Resampling is what I've been doing. Am I doing the right thing?

Second, when resampling, what is an 'anti-alias filter'? I have tried resampling with and without this and haven't really noticed much difference in the results. Should I be using it or not?

Thanks.

 

[sonusman]

Re-sampling is the ONLY way to covert back. So you are doing it right...

Anti aliasing would be important because the new 44.1 file would also have information that was higher then what is possible for the D/A converters to playback, so some kind of filtering is needed. As I recall, most hardware Re-sampling devices do this by default when sampling down. Yes, you should use it if it is an option.

Aliasing is hard to explain. It is a result of the sharp filters applied to digital audio to make sure there is no frequencies that are above half the sampling rate. Aliasing is the sort of "splashing" that results from the filters effect. Anti aliasing algorythms are designed to sort of smooth out this effect. Some are decent, some are not. But you should use it if you are sampling down.

Hope this helps.

Ed