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Well, Goran, bully for your magic tapes! ;) All of mine (Maxell, TDK and others) lost level just 
sitting around in typical northeastern US home environment conditions, and then on playback (on the 
same deck on which they were recorded) Dolby C mistracks on the high-frequency band. I would say 
that it's more high frequency dropoff than overall loss of level. I've read on this list and 
elsewhere that this problem also occurs on the professional Betacam tapes made by news 
organizations, which apparently also used Dolby C.

As I understand comments on the Ampex list and elsewhere, tapes do self-erase over time. I don't 
think anyone has figured out exactly why, have they? With a Dolby B cassette, apparently 
self-erasure doesn't result in noticeable Dolby "pumping" or other mistracking problems as quickly 
as this happens with Dolby C tapes. At least not in my experience. What happens with Dolby B tapes 
is that they get to sounding "dull" and need a treble boost to sound "lively" again. By the way, 
I've run into the same thing with Dolby A reels, with azimuth aligned with a scope, the level-set 
tones are sometimes lower than expected and in those cases it's great to have Dolby tones to get the 
CAT22 to track well on decode. I've always ascribed this to self-erasure over time. It's not drastic 
on the reels I've encountered, maybe 2-3dB at most. It seems to be more drastic on cassettes, I 
figure it's because cassettes have a much denser data-per-square-inch pack, so any sort of physical 
phenomena will have more drastic results on the audio.

-- Tom Fine

----- Original Message ----- 
From: "Goran Finnberg" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, January 14, 2011 11:43 AM
Subject: [ARSCLIST] Association for Recorded Sound Discussion List <[log in to unmask]>


Tom Fine:

> as the cassette naturally
> loses its level over time.

Naturally?

Can you give me some hard facts here, Tom.

I have asked this question approx 10 year ago directly via email to Jay
McKnight an apart from oxide shedding, external magnetic fields, magnetized
heads there is no known source why the level or treble should decrease with
time according to him.

Also....

I am asking because during 15 years I was professionally involved in a
cassette duplicating plant using Gauss, Lyrec, Ampex, King, Heino-Ilsemann,
Apex, Studer equipment etc.

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
decks.

The ONLY thing Ive seen that changes level is if the replay head is not
correctly adjusted in height and frequency response above a few kHz is
directly linked to azimuth and gap loss together with using the relevant
first orfder gap eq to correct for gap loss above approx 15 kHz.

BTW, professionally duplicating equipment set up correctly, IS capable of
such good duplicating quality that it will fool 99.9% of all listeners in
direct A/B test compared to the original sound source.  with ease.

Needless to say the loop bin master must be changed regularly as it ages for
this to hold true.

So my own experience using magnetic media for some 50 years has not turned
up any such problem practically.

Even my BASF 15"/38.1 cm/s 35S CCIR/IEC testtape dated 1968 is within 0.1
dB of a few years old MRL G320 nWb/m testtape in its reference fluxivity and
the frequency response is still within a few 1/10 of a dB to 18 kHz when
replayed on a flux loop calibrated Studer A820 despite being used +400 times
according to my log.

BASF test tapes were always hot at the high end to the tune of a dB or so to
offset user losses caused by magnetized heads, guides etc and this can still
be seen.

BASF test tapes had four repeats of the 1 kHz to 18 kHz bands and playing
repeat 3 which has only been played two times compared to the normal
frequency run shows a difference of only 0.3 dB at 18 kHz.

This test tape was recorded on BASF LGR30P red oxide tape.


-- 
Best regards,

Goran Finnberg
The Mastering Room AB
Goteborg
Sweden

E-mail: [log in to unmask]

Learn from the mistakes of others, you can never live long enough to
make them all yourself.    -   John Luther