JOPLIN M
K
II
384
k
H
z
/32bit ANALOG-TO-DIGITAL CONVERTER
REVISION P
R
A – FEBRUARY 2015
Copyright © 2015, M2Tech Srl
64
M2Tech
www.m2tech.biz
9.3. Equalizing tapes: why and when
Recording and playback heads used in tape recorders have a frequency response
which is strongly non linear and heavily dependent on the magnetic flux in the tape.
Moreover, the tape hiss increases with frequency. For this reason, also tapes are
equalized. Two equalization standards exist: NAB, mainly used in USA and Japan,
and CCIR (later IEC), mainly used in Europe. To make things more complicated,
each standard has different curves for different tape speeds, as flux changes with
speed.
The main difference between records and tapes is that almost no turntable is
provided with a built-in phono amplifier/equalizer, while almost all reel-to-reel tape
recorders are. Thus, providing tape equalizations could seem to be useless.
Not always. Reel-to-reel recorders lovers know that most of the machines around,
built between ’60 and the beginning of ’80, have generally great transports and heads
but barely adequate, if not poor, electronics. For this reason, some recorders owners
ask technicians to jump the playback circuit of the recorder, taking the signal right out
of the playback head and feeding a dedicated external amp/equalizer.
Same thing can be done with the
JOPLIN MKII
, connecting the playback head of a tape
recorder to its analog inputs (eventually via an impedance adaptor), adjusting the
gain as required and selecting the appropriate equalization curve for the tape being
played back. The signal is acquired, equalized in digital domain and sent to a
computer for recording or to a DAC or digital amplifier for real-time listening. The
ample bandwidth of the
JOPLIN MKII
set to 96, 192 or 384kHz, and its high resolution
are more than adequate to accommodate the tape recorder performance.
The
JOPLIN MKII
is provided with 4 curves for tapes, 2 for NAB and 2 for CCIR/IEC.
