On 11/23/15 7:27 AM, Tom Fine wrote:
> There is an argument to be made that analog media playback can't
> possibly offer that many data points to be collected. To wit ...
>
> 1. when you play a tape, you are fighting the laws of physics. For one
> thing, no transport provides a perfect ride across the heads.
> Resolution is damaged by wow and flutter (time-smear), plus imperfect
> tape-to-head contact cause by anything from uneven head wear to
> imperfections in the tape surface to simple dust and other particles
> in the air. There's also static electricity and other results of
> friction. Then there's the fact that some tapes are slit perfectly
> enough to ride through the transport with relatively even
> track-tracking (i.e. relatively perfect azimuth throughout the tape).
> Tape electronics, especially old ones, are prone to what are now
> considered high levels of distortion and noise, and unless they have
> been thoroughly overhauled, aging components compound these problems.
My objective, when transferring analog tape to digital, is to perfectly
capture all of the imperfections of the tape recording, without adding
any subjectively obvious errors caused by the digital recording
process. To achieve this, errors in the digital recording process must
be very much smaller than the errors in the analog recording. I assume
that digital tools to correct analog imperfections will continue to
improve, and I should therefore do a transfer which is good enough to
allow use of these improved tools in the future.
If I am only interested in capturing the audio content of a tape, I find
that using a good converter running at 96/24 is the minimum
requirement. Listening to transfers of a high quality tape recording, I
do find that I can hear a difference between 96/24 and transfers done at
lower sample rates or bit depths.
When I'm doing a Plangent transfer, I also need to capture bias. If
bias frequency is below 90 kHz, it can be captured directly at 192/24.
For bias frequencies above that, we currently use special hardware to
convert the bias to a lower frequency. To directly capture all of the
information we can currently recover from analog tape we'd need to use
768/24, which is not yet available as off-the-shelf hardware.
I don't find it very useful to ask what what level of digital
imperfections would be comparable to the imperfections in a high quality
analog tape recording.
-- John Chester
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