[Speex-dev] Notch Filter in AEC

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Wed Mar 3 03:39:08 PST 2010

The notch filter is specifically designed to cut below 200 Hz when 
working in narrowband. In wideband, the cutoff is more around 50 Hz. The 
reason is that in narrowband operation (irrespective of the codec), 
you're not really supposed to have anything below ~200 Hz, but a lot of 
people forget that.


On 2010-03-03 02:40, brant wrote:
> Hi,
>     The notch filter in AEC is only used to remove DC signal, and the time of convergence is not important, right?
> If so, I think preset value of notch_radius is too small, and it causes noticeable distortion(freq<  200hz cut).
> There is a picture in attachment to show signals under different radius in time-domain.
>    By setting notch_radius to 0.999 for all sampling rates, I found better voice effect(distortion), while AEC still
> working fine.
>         QinBin
>         cola_tin at 163.com
>           2010-03-03
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