anti aliasing filter?

[ripple_fx1]

No, they vary by whatever the sample rate happens to be....set a bit less than half the frequency of sampling.

[rosevision]

So the converter automatically adjust the cutoff according to the sample rate you choose?

[ripple_fx1]

Yes - a quick wiki will prolly explain it a lot better than I can - oversampling and the use of both analog and digital filters on AD converters make this a more involved process than simply lopping off everything above the Nyquist frequency.

[dub3000]

Originally Posted by rosevision

What is the cutoff frequency on anti aliasing filter? Do they vary depending on the company who designs a/d converters?

depends on the design - usually sample rate dependent and will vary for different manufacturers. tight filters will introduce more phase distortion, loose filters will either allow more aliasing through or cut out more super-HF content, depending on where they start/stop. there are probably other differences as well, depending on the filter design (e.g. group delay).

[Audiop]

Originally Posted by dub3000

depends on the design - usually sample rate dependent and will vary for different manufacturers. tight filters will introduce more phase distortion

Typical digital filters for this are linear phase hence no in band phase distortion.

In the analog world high order filters introduce phase shift though, higher order/sharper roll off = more phase shift/phase distortion.

In the digital world filters can be chosen to mimic analog filters with phase shift or to be linear phase or anything between.


/Peter