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

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
>>>>>> any of you
>>>>>> worked with Airshow or Plangent? If so, what has been  
>>>>>> yourexperience?