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At 11:26 AM 2010-04-29, Andrew Hamilton wrote:
>     The tape is what is biased, of course, through the heads.    It
>may be prohibitive to retrieve the signal, but if it never made it to
>the tape, then the tape wasn't biased.   The erase signal is much
>lower, at 144 kHz.  However, I see PP don't normally digitize higher
>than 192 kHz.    Even though the DSP operates at a very high F/s, far
>above that, doesn't the A/D converter performance force us to look at
>gremlins that are beneath 96 kHz?

When this discussion came up on another list, I started a list of 
bias frequencies:
http://richardhess.com/notes/2008/02/02/tape-recorder-bias-frequencies/

Despite the early work of the Austrians presented at JTS in 2007, I 
think most of us have come to believe (as George Brock-Nannestad 
stated) that the bias and audio pickup need to be coincident.

The place where this begs the question the most would be in 
stagger-track stereo recovery and I haven't thought that through. If 
you are doing this with an inline head and delay, you may wish to 
recover the bias and process the two tracks separately. I don't know 
what method would produce the greatest image stability. I wonder if 
Jamie has done this.

Maybe Cheryl can discuss this with us, or have Jamie or David tell us 
if they have ever done a stagger-head project. I'm mostly interested 
as an intellectual curiosity as I don't see many stagger-head, 
high-quality recordings, and I've seen none that have the potential 
of earning their keep and I suspect that few others have.

For many reasons, I think it is better to think of Plangent Processes 
(note it is plural) as dealing with a three-channel signal--or maybe 
even a four-channel signal--when processing a stereo master. I am not 
privy to the exact workings of PP, but it seems perfectly logical 
that bias be extracted right at the play head, filtered, shaped, and 
then possibly hetrodyned to a lower frequency for recording. Audio 
electronics are not conducive to good bias recovery and bias recovery 
electronics are not conducive to good audio recovery.

The sample minute that Jamie presented to me was amazing. There was 
no bias and he was still able to grab onto something and make the 
sound more stable. It was a tape that was recorded on a consumer 
machine (and I think I only had a cassette copy of it for the 
project)  Unfortunately, the client was not interested in funding the 
speed correction. As it was a large project, I had hoped the sample 
would convince him.

I think the Austrian's approach, conceptually, of capturing the bias 
upon ingestion is a prudent approach as then we have one more piece 
of metadata stored with the tape that will assist in superior 
reproduction should a future user of the archive wish to do so. This 
is in keeping of the bulk of the cost being borne by the future user 
and also assuming that the processes will only improve over time.

Cheers,

Richard


Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.