[BC] Re: It s Eureka over IBOC down under

[Robert Orban]

At 11:56 AM 10/21/2005, you wrote:
>From: Robert Meuser <Robertm at broadcast.net>
>Subject: Re: [BC] Re: It s Eureka over IBOC down under
>To: Broadcast Radio Mailing List <broadcast at radiolists.net>
>Message-ID: <43593D48.4040107 at broadcast.net>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>Robert Orban wrote:
>
> >
> > The FM pre-emphasis curve was more-or-less complementary to the HF
> > power handling of vinyl records using RIAA equalization. So everything
> > was pretty good back in the days of vinyl. However, the availability
> > of CD (which has flat power-handling vs frequency) eventually moved
> > the record industry to brighter mixes that pre-emphasized FM could not
> > accommodate without either reducing average modulation dramatically or
> > applying very audible HF limiting. Some would argue that today's CD
> > are mastered way too bright, but the fact remains that pre-emphasized
> > FM analog is incapable of handling this material in an audibly
> > transparent way without reducing average modulation by something in
> > the order of 10 dB compared to today's standard practices.
> >
> > Bob Orban
>
>
>While obviously you are correct, the operative word is transparent.  CDs
>need a lot of work before they can be properly (not tranparently)
>broadcast.  Some vinyl had the same problem. If the audio is made to
>conform to the 'correct' power distribution and in the case of CDs they
>are unclipped, FM transmission is improved. Digital receivers cure all
>but the pre-emaphasis issue.

I agree that "properly broadcast" is crucial, which is why one of the main 
design criteria for Orban processing is source-to-source consistency.

Regarding digital receivers, these are ultimately subject to the laws of 
physics and can't do anything about the 23 dB noise penalty in stereo 
except to blend to mono or to try some single-ended noise reduction tricks, 
which are seldom successful with all program material. Of course they can, 
in theory, use adaptive "blind deconvolution" echo cancelation before the 
detector to remove multipath. (Interestingly, this technology is crucial to 
receiving 8VSB digital television successfully, although the receiver has a 
bit more help from the TX side to guide it in setting the echo 
cancelation.) What I don't know is if any of the currently available 
digital FM receivers actually use echo cancelation technology.

Do you have any references you could point me to that provide engineering 
details for the technology that these receivers use?

Bob Orban