Dolby became necessary when everyone was using 8, 16 and then 24 tracks for rock, pop, some jazz and 
even some classical recording. I can see it being a huge benefit to keep hiss buildup at bay when 
you're combining all those tracks. However, it became an obsession in the 70's and 80's. Why was it 
necessary to be used again on a 2-track master? 15IPS 2-track on low-noise tape is very quiet, and 
the Dolby can and often does squashes the sound, making "presence" and "high end" tweaks necessary 
in LP and CD mastering. The Dolby tracking falls off as the tape self-erases, even if you set to 
Dolby tones at the beginning, as I understand self-erasure that doesn't mean that all components of 
all dynamics erased at the same rates/ratios, so the Dolby tracking should be adversely effected 
(further "deadening" the sound and "washing out" the top end).

There are examples out there from the early days of 16-track where the multitrack was running 
low-noise tape at 30IPS, no NR, and the 2-track master was recorded at 30IPS, no NR. They are not 
especially hissy. Dolby did allow economies of tape usage, no doubt there.

Sonically, it was a real mixed bag. As I understand it (having never used it), SR was a leap 
forward. I think the whole obsession with hiss was over-rated, but I agree that 16 or 24 hissy 
tracks mixed together is too noisy. If it were me producing, I would have gone with higher speeds 
and higher levels first, turning to NR only if nothing else worked. The advent and wide acceptance 
of Dolby also probably cut off some R&D in the tape world. What about thicker emulsions like 35mm 
mag-film? Also, what about 12 tracks per 2" instead of 16? That's the same track width as 3-track 
1/2" and should make for low-noise recording if low-noise tape was used at higher operating levels.

-- Tom Fine

----- Original Message ----- 
From: "Richard L. Hess" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 11, 2012 4:10 PM
Subject: Re: [ARSCLIST] Dolby Plugin

> Hi, Jamie,
> You caused me to go look at the CAT22 schematic again and I noticed some interesting things.
> (1) You're right that there are odd diode-ninja things in he drive to the FETs, but there are also 
> two FETs driven from the same line, producing, what would appear at first glance, a steeper 
> attenuation slope.
> (2) There is another nasty thing--fairly hard diode clipping (which isn't as hard as digital 
> clipping as you know) on the base of the compressor's audio output emitter follower. Joy!
> I'm glad I've got a bunch of CAT22 cards to carry me into the future.
> Fortunately, failure modes appear to be MOSTLY coupling caps.
> Cheers,
> Richard
> On 2012-01-11 3:12 PM, Jamie Howarth wrote:
>> They also do some weird attack and release ninja with diodes that is really hard to mock up. The 
>> while enchilada has strange xfer curves beyond just the compression ratio, bandpasses, and 
>> thresholds-  which is why they invert-added through the same screwball circuit - building two of 
>> these won't match.
>> Knowing what I know now about this self-nulling circuit and tape compression there's no way it 
>> can't be heard mistracking. Comparing a dolby a encode-immediate-decode through wire is audible 
>> if the dolby dot levels are even slightly mismatched. Off tape it's hilarious. Of course who 
>> likes hiss...
>> But that's why hot 15IPS or hot 30IPS was the preferred "evil" ... Dolby a changes stuff a lot.
> -- 
> Richard L. Hess                   email: [log in to unmask]
> Aurora, Ontario, Canada           (905) 713 6733     1-877-TAPE-FIX
> Quality tape transfers -- even from hard-to-play tapes.