[BC] Achieving good S/N

[Robert Orban]

At 01:01 PM 12/26/2005, you wrote:
>From: "Steve" <shnewman at alaweb.com>
>Subject: Re: [BC] Achieving good S/N
>To: "Broadcast Radio Mailing List" <broadcast at radiolists.net>
>Message-ID: <001501c60a5d$9bf81180$7402a8c0 at wildblue.com>
>Content-Type: text/plain;       charset="iso-8859-1"
>
>
>Dave...to be honest with you it's a figure I was given by the transmitter
>maint. guy. I think it was Stereo but could have been mono. I really can't
>remember how he did his testing. However, being that we had an audio guy
>(freelancer from Ampex) and a transmitter guy (think he was with Lockheed)
>I'll bet this was measured at the transmitter. Oh, you asked if our studio
>was at the transmitter or hooked via phone lines. We were in downtown San
>Francisco using 15Kc loops to Mt. San Bruno. (where most all the TV's and
>FM's were at the time) We used Langevin line amps to drive the phone lines.
>Now, I distinclty remember turning the transmitter on Saturday and Sunday
>mornings (hey I was 17 y.o. and a part-timer board monkey) and that carrier
>was dead quiet on the Tannoy's. We were quiet alright. Real quiet. Guess
>that's one of the reasons we were 1 out of  7 stations in America to win the
>Hi-Fi Stereo Review award for best audio. The owner gave the word perfection
>a whole new meaning.  I think I want to go back to the days of the Conax
>FM processors.  Well, for Classical music formats, anyway. (that was the
>format at KSFR) You may have seen my post where I said you couldn't tell the
>difference between listening off the turntable or the on-air monitor. It was
>really amazing. Bob Orban remembers the station and will attest to what I'm
>saying.

Yep...it had first rate audio.

The Conax was a clever device for its time (it was essentially a dual-band 
processor with a clipper in the HF band only),  but current processor 
technology could do far better in terms of HF clarity while still retaining 
as much dynamic range as the broadcaster desired. I'm quite familiar with 
the Conax; we had one on WPRB when I was active there while in college. It 
replaced a Gates pre-emphasized clipper (I forget what its actual marketing 
name was) that splattered on every "ess." The Gates only lasted a week 
on-air before I sent it back.

Originally, we used no audio processing at all on that station. The mod 
monitor's peak flasher was extended into the control room, and the operator 
was expected to ride gain appropriately. The flasher was relay-driven, and 
the give-away was hearing live mic in the control room with the relay 
clacking away in the background! Eventually, I designed and built a simple 
audio processor using optical attenuators (like the LA-2). The Conax was 
used for pre-emphasis control.

However, the Conax would have a lot of problems with the HF content on 
today's CDs. As program material gets brighter, one can no longer rely on 
clipping alone to control HF energy. When I was designing the 8100, I was 
originally hoping to be able to use distortion-canceled clipping with no 
program-adaptive-filter-type HF limiting in the 8100 design, but I found 
enough material even back then that made the "clipping-only" solution sound 
too distorted.

Bob Orban