From: Patent Tactics, George Brock-Nannestad


I think that I am in need of some instruction here because I am probably 
stuck in some old-fashioned thinking about the magnetic recording process.

Shai Drori wrote:

> I meant  that the recorded signal is so high that it is not present on 
> tape, I think that is the magic of it. It still biases the heads but 
> it's just too high for the tape itself.

----- now, to my old-fashioned thinking the heads are made of a soft magnetic 
material with a very narrow hysteresis curve and no remanence to speak of, 
and so they do not really need any bias to function. However, usually, the 
tape itself is a hard magnetic material with a high remanence and so benefits 
from bias, preferentially HF bias. You used to push the bias up in frequency 
so as not to get intermodulation distortion when you replayed your tape, and 
the limited bandwidth in the tape amplifier would ensure that you did not get 
any spill-out of the bias frequency, even if the head could catch it 

At present I can simply not understand how a noise-free (as far as it goes) 
recording can be obtained without biasing the magnetic particles on the tape. 
The only working case I know where you could say that the programme material 
might have an influence on the bias level is in the HX-Pro system, invented 
by Bang & Olufsen in Denmark and licensed to Dolby Laboratories. Another 
possibility is that ATR are making use of an old invention by Sangamo Weston, 
which uses a noise signal as bias. That cannot be detected upon replay and it 
cannot make intermodulation distortion as we fear it.

If someone really has come up with an improvement on bias I shall eagerly 
want to study it.

Kind regards,


Shai Drori continued:
 Don't forget that at 15ips 
> you're describing a theoretical 56kHz at 1 7/8 ips. It's just not there. 
> I love it. I like the way it sounds much better than the reocridngs I 
> made on otari or Studer, dare I mention tascam. I can see the benefits 
> of this system for film, but for nice audio tape in good condition, an 
> ATR recording will be hard to lock to. Did they transfer any command 
> recordings? I would love to hear the Borelo!!! What a recording (I know 
> I will now ge tons of emails about my taste in music. In my defense, my 
> wife would be on your side and add her thoghts about my clothes as well).
> Shai
> On 4/29/2010 1:52 PM, Andrew Hamilton wrote:
> > Dear Shai,
> >      As I wrote in your quoted response, below, there are other 
> > signals besides bias that the PP can lock to.   They mention "logic 
> > control" signals.   I suspect there are other ghosts they could bust.
> >      The ATR is only bias-free while reproducing.   But when 
> > recording, it should be present, at 432 kHz - almost as high as the 
> > Dave Hill Aria bias.  Even if you recorded at 30 ips and then, on 
> > playback, select 3.75 ips and then also  vari-speed the oscillator to 
> > 50% of that, the 432 kHz bias signal would still be at 27 kHz.  Did 
> > you remember to digitize at 2x F/s?  Otherwise, it would have been 
> > filtered out by the ADC.
> >
> > Please audition the samples on the PP website.  They made a believer 
> > out of me.   There's a Waves plugin to inject wow and flutter into a 
> > digital recording.   The PP would not be able to undo this since it is 
> > simulated and does not contain a veiled clock.
> >
> >
> >
> >
> > Andrew
> >
> >
> >
> >
> > On Apr 29, 2010, at 5:53 AM, Shai Drori wrote:
> >
> >> I can see that working with 160 or even 200 (you can hear it if you 
> >> slow down the tape enough), but the ATR is bias free, at least on 
> >> tapes I made so far. The system is interesting though. How does it 
> >> monitor to see that the original bias did not drift while recording? 
> >> This would make you track the wrong frequency..
> >> Shai
> >>
> >> On 4/29/2010 10:24 AM, Andrew Hamilton wrote:
> >>> There are other forensic time stamp signals besides bias which would 
> >>> allow for an ATR-100-recorded tape to be de-fluttered by the PP 
> >>> DSP.   However, even though a tape may be played back by the Airshow 
> >>> ATR-100, it's entirely possible that the tape was recorded elsewhere 
> >>> by a different machine (having a much lower bias f).  I believe that 
> >>> Airshow are offering this service with PP for already-existing 
> >>> analog tapes, rather than for creative layback transfers.
> >>>
> >>> David Glasser is chief engineer at Airshow and he has mastered a 
> >>> huge amount of audiophile CDs, DVDs, and SACDs.   Great ear; great 
> >>> rooms; great gear.
> >>>
> >>>  From the PP website:
> >>>
> >>> "software algorithm, developed with researchers at Cambridge 
> >>> University in England, which identifies a steady-state ultrasonic 
> >>> reference tone (such as tape bias or logic control) embedded within 
> >>> the original analog signal and then performs continuous 
> >>> high-resolution pitch correction in order to keep the reference tone 
> >>> at a fixed frequency..."
> >>>
> >>>
> >>>
> >>> Andrew
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> On Apr 29, 2010, at 4:15 AM, Shai Drori wrote:
> >>>
> >>>> My experience with the ATR is just the opposite. I have tested 
> >>>> various transport and some tapes were handled only by the ATR. Does 
> >>>> the system figure out bias frequency automatically. What does it do 
> >>>> with tapes recorded on the atr where the frequency is so high it 
> >>>> doesn't show up on playback (400kHz+)?
> >>>> Shai
> >>>>
> >>>> On 4/29/2010 8:54 AM, Paul G Turney wrote:
> >>>>> Well they only use ATR 102 machines which are notoriously rough 
> >>>>> tape handlers....
> >>>>>
> >>>>> They use software to track and maintain a bias frequency so that 
> >>>>> any speed anomolies are and wow and flutter are reduced by 
> >>>>> maintaining perfect pitch with this tone.
> >>>>> Not worked with Airshow mastering.
> >>>>>
> >>>>> It appears to be a monopoly on the software so Airshow would be 
> >>>>> subbing the work out to PP.
> >>>>>
> >>>>> PT
> >>>>>
> >>>>> -----Original Message-----
> >>>>> From: Chandra Lynn [mailto:[log in to unmask]]
> >>>>> Sent: Thursday, April 29, 2010 02:12 AM
> >>>>> To: [log in to unmask]
> >>>>> Subject: [ARSCLIST] Airshow Mastering&  Plangent Processes
> >>>>>
> >>>>> I noticed some earlier postings about Plangent Processes. It 
> >>>>> eliminates wow,flutter and speed aberrations from analog masters. 
> >>>>> They are now working withAirshow Mastering to offer optimized tape 
> >>>>> transfers. The announcement is onAirshow¹s site at 
> >>>>> any of you 
> >>>>> worked with Airshow or Plangent? If so, what has been
> yourexperience?
> >>>>>
> >>>>>
> >>>
> >