[asterisk-users] Silk for Free

[Michael Graves]

On Fri, 06 Mar 2009 02:15:12 +0800, Steve Underwood wrote:

>Steve Underwood wrote:
>> They might be doing some kind of fake bandwidth expansion. You can't 
>> create something out of nothing, and make the narrowband voice more 
>> intelligible, but you can make it sound pretty nice. Jean-Marc Valin (he 
>> of speex fame) has a very impressive expander he is working on at the 
>> moment.
>>   
>Someone tells me Polycom definitely do some form of bandwidth expansion, 
>though its a lot less realistic than Jean-Marc technique.

What do you mean by "bandwidth expansion?" 

The term expansion in audio is most commonly used in reference to
dynamic range. Expanders (and their inverse, compressors) vary the
level of a signal dynamically to effect changed signal.noise ratio.

How does one effect frequency domain extension? That seems
counterintuitive to me. Frequency response (pass-band) is a function of
sampling rate (see Nyquist) and anti-aliasing filtering.

Michael
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