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I think that Doug's approach, using multi-channel A-D conversion is preferable to sequential passes. An item not discussed (as far as I've seen) in this thread is the sample-clock-to-audio phase lock. If you look at sampling theory, there can be a very large difference in individual numbers while still maintaining the same information. I ran into this doing a second pass on a tape and while zoomed out the waveforms looked the same (I was looking to cut into and out of a damaged section I had been able to get a better transfer of), once I zoomed in to the sample level, the individual samples were very difficult to match and it was hard to line up sample-accurate cut points. The way to do it is to look for relative energy under the curve as you are aligning. All this suggests that a method of starting and maintaining the timing accuracy among the multiple copies AND the A-D sample clock (to the tolerance discussed below) seems to be a good idea. The auto image alignment that is being done can be more or less successful, depending on the raw input. I'm impressed my hand-held cell phone camera can do as good HDR images as it does, but they are by no means as good as a tripod-based PhotoShop version. I'm certain that software will progress to do this. Michael Gerzon alluded to some possibilities of track-splitting on tape to help improve capture in his 1976 article posted here: http://cec.sonus.ca/education/archive/10_x/gerzon_archive.html As we discuss the new economy, I wonder how this work will be funded. Cheers, Richard On 2012-06-22 10:30 AM, Doug Pomeroy wrote: >> >>> Date: Wed, 20 Jun 2012 10:44:42 +0100 >>> From: Ted Kendall <[log in to unmask]> >>> Subject: Re: audio from pictures >>> >>> <<SNIP>> >>> >>> Chris Hicks of Cedar did his doctorate on just this question of >>> multiple >>> copies. When the algorithm could be persuaded to work, the results were >>> much as you would expect - enhancement of the correlated wanted signal >>> and reduction of the random noise. Unfortunately, pulling the >>> recordings >>> into good enough sync for artifacts to be negligible was a frustrating >>> and difficult business, even with recordings made one after the other >>> (by me, as it happens) on the same kit on the same settings on the same >>> afternoon, with meticulous centring. <snip> > I gave a talk on this subject at the ARSC conference in Nashville in > 1997. > Two perfectly synchronized copies would provide a theoretical > signal-to-noise > improvement of 3 dB, four copies an improvement of 6 dB and eight > copies an > improvement of 9 dB. The first problem is finding so many copies in E > condition. > > But the bigger problem is how to achieve perfect synchronization. > John S Allen of the Boston Audio Society discusses this matter in an > article he > wrote for the Spring 1990 issue of the ARSC Journal. He says the > accuracy of > sync must be "about ten microseconds (72 degrees of phase shift at 20 > kHz)". > No real-world turntable is stable enough to achieve this result on > successive > plays, and I proposed a stack of tables all powered by a single motor for > playing the discs simultaneously, with use of digital delay lines to > align > the audio from them after transferring. > -- Richard L. Hess email: [log in to unmask] Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX http://www.richardhess.com/tape/contact.htm Quality tape transfers -- even from hard-to-play tapes.