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The question about the bias signal was batted around on the Ampex List when Jamie Howarth first 
introduced his process.The conclusion was, it was more likely than not that bias was steady enough 
to be pretty immune to wow and I think also flutter on almost any given tape. However, bias 
frequency is often not exactly what was specified, especially on older machines. But in the real 
world, I'm not sure if this has proven true, perhaps Jamie or David Glasser will comment -- is the 
actual bias frequency usually or often about or exactly what the manufacturer specified? Even in 
older tapes? What about old mag-films? As I recall the Ampex List discussion, this was likely less 
of an issue when you get to the second-generation solid-state machines due to better power supply 
regulation and generally improved power transmission in major cities by the late 60's. One of the 
big issues with tapes made early on was that the AC capstan was dependent on AC power line 
frequency. Apparently, in some parts of the country, this was not always 60hz. So having a known 
bias frequency would seem to matter in all of his, but perhaps the final product is ear-tuned to the 
music pitch?

Jamie had very good results not only sync'ing to but also removing Fairchild Pic-Sync tone in some 
samples I gave him. The results were audibly superior to a dub played back thru a Pic-Sync 
demodulator back in the day.

-- Tom Fine

----- Original Message ----- 
From: "Mike Gray" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, April 29, 2010 12:46 PM
Subject: Re: [ARSCLIST] Airshow Mastering & Plangent Processes


> What a simple and elegant idea - use the bias signal as a clock; wow+flutter=jitter; heterodyne - 
> same as recovering audio modulation from an RF signal.  Congratulations to all involved.
>
> One criticism I heard when I mentioned this technique to someone in the restoration community - is 
> the bias signal sufficiently stable to ensure that the derived signal is accurate?
>
> Just my 2 cents,
>
> Mike Gray
>
>
>
> David Glasser wrote:
>> I can answer some of the questions raised about Plangent, the need for specialized replay 
>> electronics and heads, and the machine at my company, Airshow:
>>
>> 1) The bias signal was never intended to be recoverable. That this is possible is a happy 
>> accident, but stock replay electronics and heads - by design - will not reproduce the bias 
>> signal.
>>
>> 2) The Plangent replay electronics and playback head have several features designed to make bias 
>> signal recovery possible - the head itself is a wide-bandwidth design and the first amplification 
>> stage is built into the headblock itself. The Plangent electronics are designed for 
>> wide-bandwidth, low noise reproduction, and they do not have a bias trap filter. The bias signal 
>> of most tape recorders is too high in frequency to be captured at 192kHz, but the Plangent 
>> electronics contain a very clever heterodyne mixer that will downconvert the bias signal, after 
>> its nominal frequency has been identified, to 24 or 48kHz which is easily captured by 96k or 192k 
>> conversion (and recorded to a separate digital track). A dedicated bias output feeds a PC-based 
>> spectrum analyzer used to identify the bias signal. An earlier incarnation of Plangent used a 
>> separate head to recover the bias. A separate head is no longer used. The electronics were 
>> designed by the late David Smith, and refined and hand-built by John Chester. We will post photos 
>> of the electronics, etc on the Airshow website soon.
>>
>> 3) Bias from a tape recorded on an ATR-100 is indeed not recoverable. ATR-100 tapes, however have 
>> other tell-tale signals that can be used as a reference. The ATR's logic circuits emit rf noise 
>> at several frequencies and tend to bleed into the record circuitry. For example, simply turning 
>> off the ATR's LED time display eliminates several noise spikes observable on our spectrum 
>> analyzer. (Consequently, we have installed an on/off switch on the display.)
>>
>> 4) While the transport of an ATR is not as gentle as a Studer A820, it can be safely used for all 
>> but the most fragile tapes. If we see enough of a demand for this service, we will add Plangent 
>> heads to our A820.
>>
>> 5) The Plangent processing is done at Jamie Howarth's lab in Massachusetts. We are only offering 
>> optimized transfers, and a conduit to Plangent's services.
>>
>> 6) As tape speed drifts, so to will the frequency of the recovered bias. For this reason, 
>> Plangent recommends that a reel be transferred song-by-song, and the bias frequency identified 
>> for each song. This obviously can increase the time and cost of the transfer.
>>
>> 7) All of this would be besides the point if it didn't sound good. The Plangent replay 
>> electronics are on a par with other high-end tape replay electronics like the Aria. I am 
>> naturally skeptical of digital signal processing, especially processing on the scale of the 
>> Plangent Process, but after hearing some of Jeffrey Norman's Plangent-processed Grateful Dead 
>> masters, I am convinced that this is a major breakthrough in audio restoration technology.
>>
>> I've been involved in audio restoration for many years, but am new to the ARSCLIST, so I 
>> apologize if this post is inappropriate. We are very excited to be associated with Plangent, and 
>> I invite anyone who is interested in this technology to contact me directly, or contact Jamie at 
>> Plangent.
>>
>> David Glasser
>> Airshow Mastering
>> Boulder, CO
>>
>> www.airshowmastering.com
>> 303-247-9035
>>
>> On Apr 29, 2010, at 7:31 AM, Shai Drori wrote:
>>
>>> Hi Andrew
>>> 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. 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
>>>>>>>> http://www.airshowmastering.com/plangent.htmlHave any of you
>>>>>>>> worked with Airshow or Plangent? If so, what has been yourexperience?
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>