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?
>>>>>>>
>>>>>>>
>>>>>
>>>
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