[Speex-dev] Notch Filter in AEC

[QianBin]

Steve Underwood,


>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.
Yep, just uncompressed :)
>
>Steve
>
>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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　　　　　　　　QianBin
　　　　　　　　cola_tin at 163.com
　　　　　　　　　　2010-03-03