[mdlug] Converting tapes

[Aaron Kulkis]

Michael Rudas wrote:
> --- Carl T. Miller wrote:
> 
>> I have a friend that needs some audio tapes converted
>> to CDs.  Do you know of anyone locally who provides
>> this service?
> 
> It's EXTREMELY trivial to do this at home.  Why pay for the service?
> You can borrow a cassette player, or pick one up at a thrift
> shop--just make sure it's got Dolby.

Also a Type I/Type II selector switch at the very least
(and preferably Type III/Type IV as well).

To get nice, linear response (that is, that the strength
of the magnetic fields stored on the tape are linearly
proportional to the original signal), the tape is first
subjected to an AC signal, referred to as the "Bias Tone",
which makes the magnetic coercivity of the recording
material more linear by more or less eliminating the
magnetic hysteresis effect.

http://en.wikipedia.org/wiki/Hysteresis

The reason is that to record something on iron, it's easier
if you first subject the tape to an oscillating magnetic field,
and so whatever frequency is used for that oscillator is
called the "bias frequency".


http://en.wikipedia.org/wiki/Tape_bias


Type I is for the original formulation for tapes,
used Iron(II)oxide (Fe2O3) for  the actual media

Type II was the improvement using FeCr, typically
denoted as "Chrome", and uses a different bias
frequency than Type I.

Type IV is "metal" uses un-oxidized iron which uses
an evaporative sputtering process to deposit the
medium onto the tape substrate.  Uses the same
bias frequency as Type II, but at a different
field strength.

For playback, I BELIEVE that all you need is a two
position switch to choose between Type I and Type
II/III/IV switch (types II - IV all use the same
bias frequency), but I'm not totally sure about that.

Also, you might want to put the bias switch in
the "wrong" position... sometimes, playback with
the circuitry set for the "wrong" frequency results
in slightly better sound.

Lastly, some machines automatically detect which
type (I, II, III, or IV) by the size and position
of notches in the case.  While this is great for
recording, it's not so good for playback, as the
tape might not have been recorded at standard
bias frequency for that type -- so look for a
tape player with a selector switch.