Drawmer 1962 Digital Vacuum Tube Pre-Amplifier - Manual (Page 15)

1962 OPERATORS’ MANUAL 11
HIGH & LOW PASS
The high and low pass filters are included to allow the user
to attenuate undesirable sounds at the extremes of the audio
spectrum, such as rumble, hum or hiss. They may also be
used for creative applications, either on their own or in
combination with conventional EQ. In order to make these
filters effective in a variety of situations, they have been
designed with fixed slopes and variable frequencies. Closing
the two filters down so that any audio being converted to
digital passes through unaffected can improve the signal-to-noise ratio of the digital data.
High-Pass:
A continually variable, 12dB per octave shelving, high-pass filter which may
be adjusted over the range 15Hz to 400Hz. It may be used, for example, to
attenuate microphone stand noise, traffic rumble or excessive low
frequencies caused by a less than ideal choice of mic position. It may also be
used to reduce the amount of low frequency spill from an adjacent instrument
when the source being recorded is in a higher register than the source of
interference. The High-Pass filter is also helpful in reducing the level of the
fundamental frequency in mains hum, though it will not remove the harmonics
that cause mains buzz .
Low-Pass:
A continually variable 12dB per octave shelving, low - pass filter which may
be adjusted over the range 2kHz to 42kHz. It is useful in attenuating high
frequency hiss or noise, especially where the programme material only
contains low to medium harmonic frequencies - for example, electric guitar
or bass tracks.
In:
Switches both the Low- and High-Pass filters into, or out of, circuit. A red LED
indicates that the filters are in circuit. If only one filter is required, the other
should be set to the extreme of its frequency range so as not to affect the
signal being processed.
FINE TUNE EQ
The three controls in this section provide a subtle
degree of control over the audio and are
designed for audio sweetening rather than for
radical signal reshaping. This section should not
be confused with the type of equalisation that
might be offered on a mixing desk or parametric
type unit.
A rear panel insert jack is connected in series with the Fine EQ section, so the In/Out button
simultaneously bypasses any external processor connected via the channel insert point.