A friend of mine (who would rather not be dragged into more
conversations about this) who worked in the Ampex Standard Tape Lab, and
who is not part of this list, reported to me that no one could explain
why, but some cassettes that were recorded would lose high frequencies
if stored for about a year. The loss was substantial. While Don no
longer has any notes on this, I have generally found his memory and
knowledge to be reliable. His recollection is that the 15 kHz loss was
in the neighbourhood of 10 dB in the worst examples.
I have grilled him on this, and he is convinced that it happened and it
was not due to external magnetic fields.
One theory that was proposed at the time was magnetostriction due to the
relatively small radii of the guides in the cassettes.
He used Dragons and other top-end cassette machines in the lab. He was
responsible for a while for manufacturing Ampex standard "test"
[calibration] tapes for audio and video.
On 2011-01-14 11:43 AM, Goran Finnberg wrote:
> None of the high speed duplicated cassettes I still have, several 100, and
> none of my approx 60 BASF, Nakamichi and RCA test cassette tapes show any
> change in level or frequency response either objectively or subjectively IF
> the azimuth is very carefully adjusted on my Dragon, 582 or 682 Nakamichi
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Quality tape transfers -- even from hard-to-play tapes.