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From: emrath@uiuccsb.UUCP
Newsgroups: net.audio
Subject: Re: Bias Adjustment in Cassette Decks - (nf)
Message-ID: <6350@uiucdcs.UUCP>
Date: Fri, 23-Mar-84 22:29:05 EST
Article-I.D.: uiucdcs.6350
Posted: Fri Mar 23 22:29:05 1984
Date-Received: Sun, 25-Mar-84 12:37:20 EST
Lines: 27

#R:umcp-cs:-606200:uiuccsb:5700030:000:1516
uiuccsb!emrath    Mar 23 14:52:00 1984

You should make the bias adjustment with Dolby off.
If everything else is just perfect, then it wouldn't make any difference.
If the response changes significantly when you switch Dolby in,
then it (usually) means the Dolby en/decoders are mistracking.
The absolute sound level is important for the decoder to properly decode
the signal. This is normally achieved by adjusting the gain of the recording
amplifier (rather than the playback preamp), and should be done when changing
from one brand of tape to another. Note that this adjustment is made *after*
encoding, while the overall recording level is set *before* encoding.
It makes a difference.  My deck has the appropriate test tones and record
amp adjustments, so setting record level and bias is fast, easy and accurate.
An error of 2-3dB in record level makes a noticable difference in the response
of low-level FM hiss (-15dB) when switching Dolby-B in/out (I just tried it).
Dolby C just makes the problem worse.  Since tapes can vary this much, even
within the same brand, this may be your problem.
Note: FM hiss is a very good way to adjust the record bias, for it is a very
demanding signal.  But just because you hear a change when you switch in the
dolby circuits, that doesn't mean the sound of typical signals (i.e. music)
will be seriously defected. If you can't live with it, you'll have to check
the Dolby record level and if this is your problem, come up with a way to
adjust it.

	Perry Emrath, UofIL
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