[Vintage-Audio] Re FM Multiplex

[Salmons, Michael]

Hi Duane,

Sounds like the equalization you speak of may have given the user some
room to tweak a dolby B-encoded FM broadcast. Dolby FM worked well at
its conception, reducing perceivable hiss at the high end by as much as
9db. As the high end of FM transmissions increased, it became harder to
control signal noise. Thus the ability to adjust the rolloff frequency
that unit probably has. I doubt it's of any use nowadays, unless you can
use it to tweak your own Dolby-B recordings in playback?

Here's a web page dedicated to a description of the Dolby FM phenomenon.

http://www.vintagebroadcasting.org.uk/dolbyfm.htm

Cheers,
Michael 

> -----Original Message-----
> From: vintage-audio-bounces at mailman.qth.net 
> [mailto:vintage-audio-bounces at mailman.qth.net] On Behalf Of 
> Duane B. Fischer, W8DBF
> Sent: Thursday, January 20, 2005 10:58 PM
> To: vintage-audio at mailman.qth.net
> Subject: [Vintage-Audio] Re FM Multiplex
> 
> 
> 	
> Hi All, 	
> 	
> I have here this beautiful contraption called a Teac AN-180. 
> Impressive front panel! Way cool! Sold for $350 about 1974. I 
> even have the rare calibration
> cassette tape too! Yes, even a manual. Seriously cool dudes!	
> 			
> 	
> Now this beauty will allow the owner of equipment not having 
> Dolby to both record and playback in full Dolby. Especially 
> nice if you own a high end Revox
> B77 which lacks Dolby! It also appears to allow the owner to 
> use Dolby with FM? 
> 
> 	
> The front panel looks like something from a Space Shuttle 
> console. All sorts of switches, knobs, meters, lights and so 
> forth. As I said, way cool! But what is all of this about 
> 'equalization'? No, not the EQ with +/- for different 
> frequencies. This is a kind of sound equalization, sort of 
> like the bias
> adjustment. (a poor comparison)	
> 	
> What does this equalization do here anyhow? There seems to be 
> a relationship to
> FM as well as some other devices that can be fed through it.	
> 	
> Wasn't FM broadcast at one time with Dolby? Or am I having a 
> vintage daydream here? It did not last long, nobody cared and 
> it was quickly gone. So fast, many
> never even knew it ever existed.	
> 	
> Hopefully one of you wizards of audio can explain to me what 
> the AN-180 does
> besides the Dolby. Thank you.	
> 	
> Duane W8DBF	
> 
> 	
> 
> 	
> 
> 	
> 
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