[BC] IBOC AM Quality

[Dana Puopolo]

Most codecs don't particularly like many band dynamics processing either, as
it screws up the perceptual coding. An example...

Perceptual coding works because it models how humans hear (dogs might hear
MP3's as buzz for all we know). One of the big things is that humans can not
hear two closely spaced tones if one is a certain level above the other. We
only hear the louder tone; therefore the codec says: 
"I can remove the second tione because it's redundant". Problem is, if you
have a many band processor (or a lot of IM as Frank says), the second tone's
level is affreced and it screws up the codec.
Frank and the other processor manufacturers realize this and so they limit
multiband processing for codecs to four or five bands total.
One other thing-processing needs to be changed when bit rates change.

-D


------ Original Message ------
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From: "Powell E. Way III W4OPW" <w4opw at yahoo.com>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Subject: Re: [BC] IBOC AM Quality


--- padrino <padrino at telos-systems.com> wrote:

> No amounts of 'whacky-tobacky' needed. :)


For US that is. 

 
> Processing for lower bitrates requires that the
> audio processing is NOT
> what we've come to know. Research has shown that low
> bitrate codecs DO NOT
> like clipping...NOR...limiting that contains high
> levels of
> intermodulation distortion (IMD). Most dynamic peak
> limiters exhibit high
> IMD and this causes added 'artifacting' in the
> coder. Just spent a good
> year working on this, and the proof is in the
> processing algorithms.

> -Frank Foti


But getting the GM or PD to understand this may be
  E X  C E P T I O N A L L Y       hard to accomplish.



Powell



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