Re: [codec] draft test and processing plan for the IETF Codec

[Koen Vos <[e-mail]>]

Paul Coverdale wrote:
> You mean that VoIP applications have no filtering at all, not even
> anti-aliassing?

The bandpass filter in the test plan runs on the downsampled signal, 
so it's not an anti-aliasing filter.  

Also, the plan's bandpass for narrowband goes all the way up to Nyquist 
(4000 Hz), whereas for wideband it goes only to 7000 Hz.  So if the 
bandpass filters were to somehow deal with aliasing, they are not being 
used consistently.

I presume the resamplers in the plan use proper anti-aliasing filters 
representative of those in VoIP applications (and described in 
Jean-Marc's post).

best,
koen.


----- Original Message -----
From: "Paul Coverdale" <[e-mail]>
To: "Koen Vos" <[e-mail]>, "Anisse Taleb" <[e-mail]>
Cc: [e-mail]
Sent: Saturday, April 16, 2011 4:42:06 AM
Subject: RE: [codec] draft test and processing plan for the IETF Codec

Hi Koen,

You mean that VoIP applications have no filtering at all, not even
anti-aliassing?

...Paul

>-----Original Message-----
>From: [e-mail] [mailto:[e-mail]] On Behalf
>Of Koen Vos
>Sent: Saturday, April 16, 2011 1:04 AM
>To: Anisse Taleb
>Cc: [e-mail]
>Subject: Re: [codec] draft test and processing plan for the IETF Codec
>
>Hi Anisse,
>
>I noticed your plan tests with band-limited signals: Narrowband signals
>are
>filtered from 300-4000 Hz, Wideband from 50-7000 Hz, Superwideband from
>50-14000 Hz.
>
>However, VoIP applications have no such band-pass filters (which degrade
>quality and add complexity).  So results will be more informative to the
>WG
>and potential adopters of the codec if the testing avoids band-pass
>filtering as well.  We want test conditions to mimic the real world as
>closely as possible.
>
>Instead of band-pass filtering, tests on speech could use a simple high-
>pass
>filter with a cutoff around 50 Hz, as many VoIP applications do indeed
>have
>such a filter.
>
>best,
>koen.
>
>