JOPLIN
384
k
H
z
/32bit ANALOG-TO-DIGITAL CONVERTER
REVISION P
R
A – SEPTEMBER 2012
Copyright © 2012, M2Tech Srl
36
M2Tech
www.m2tech.biz
on. Not only: her English branch, Columbia England, developed her own curve for 78rpm’s
cut in Great Britain.
9.2.17. Decca FFRR 78rpm (DEC)
This is the equalization curve for 78rpm used by Decca, from which the LP FFRR was later
developed.
9.2.18. MGM 78rpm (MGM7)
Before cutting LP’s, MGM produced 78rpm’s, which were cut using MGM proprietary curve
for 78rpm.
9.2.19. Victor 1938-47 and Victor 1947-52 (VIC3 and VIC4)
Victor is an old company, later purchased by RCA, who produced 78rpm since 1925. The
curve adopted between 1925 and 1938 is same as Columbia type 1925 (See 9.2.16), later
curves are offered with specific choices.
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
, 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
set to 96, 192
or 384kHz, and its high resolution are more than adequate to accommodate the tape
recorder performance.
