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.