Allen&Heath 21 Series - Manual (Page 16)

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inputs for tape signals are preset to a standard signal level
(0VU = +4dBm). There are however three standard signal levels
that different tape decks may produce:
0VU = +4dBm (1.23V RMS)
0VU = 0dBm (0.775V RMS)
0VU = -10dBV (0.3lV RMS).
Consult the page of this book "Tape deck interface" for
guidance on obtaining the best from the tapedeck - console
system. Your Allen and Heath console is engineered to work
perfectly with all three standard level systems.
The important point is that the signal level between console
and tape deck that corresponds to 0VU is the operating level
of your studio system and when console and tape machine are
in agreement you have a fair chance of making good recordings.
Once again your ears are the final judge of the off-tape
quality and may lead you to overrule record level meters.
Use the console monitor section "tape" switch to check the
off-tape quality. You will usually hear added noise but more
importantly listen for added distortion. Tape is operated
much nearer its overload point than console system amplifiers.
Your console amplifiers deliver rated performance (below
audibility) at all signal levels right up to the onset of
clipping 18dB above 0VU. The audio amplifiers in most
modern tape decks are similarly blameless. Tape however
typically generates 3% third harmonic distortion only 8
to 10dB over 0VU recording level and more bad sounding
tapes are made as a result of recording too hot than through
.
clipping console amplifiers. Not only that but tape overloads
sooner at high and low frequencies than at mid-band frequencies
(the 1kHz reference point) so imagine the distortion figures
at 100Hz and 10kHz where bass and strings come.
The point of this is - do not expect the hardware to perform
the impossible, it is already performing a miracle by
comparison with full blown record house equipment of the
early days of sound recording, get the console-tape deck
interface right and learn the capabilities of the audio
amplifiers and tape you use.