[Speex-dev] Notch Filter in AEC

Steve Underwood steveu at coppice.org
Wed Mar 3 05:17:14 PST 2010

Hi Jean-Marc,

You make that sound like its just a matter of meeting some arbitrary 
spec. Let's be more specific.....

If you use narrow band voice down to deep bass frequencies:

     - 16 bit linear audio sounds good
     - alaw or ulaw sounds muddy
     - low bit rate codecs, like speex or G.729, sound awful.

I assume QinBin only listened to some uncompressed audio in his evaluation.


On 03/03/2010 07:39 PM, Jean-Marc Valin wrote:
> 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.
> 	Jean-Marc
> 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.

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