Input Fader; High-Pass Filter - Sound Devices 664 User Manual And Technical Information

664 User Guide and Technical Information

Input Fader

The Input Fader is the primary control used while mixing and it affects
the level of the Input signal routed to all post-fade destinations. Use the
Input Fader to make fine gain adjustments. The fader can be attenuated
from off (full counter-clockwise position) to +15 dB above the set Trim
level (full clockwise position). To optimize gain structure for the best per-
formance, operate input faders at or near the 0 dB (unity gain) position.

High-Pass Filter

Each input channel has an adjustable high-pass filter controlled by the High-Pass Filter control. High-
pass (or low-cut/low roll-off) filters are useful for removing excess low
frequency energy from audio signals. Wind noise is a common unwanted
low frequency signal that can be reduced with the use of a high-pass filter.
For most audio applications, engaging the high-pass filter is beneficial, be-
cause audio information below 100 Hz is rarely used, especially for speech
reproduction.
The 664's high-pass filter circuit features an adjustable corner (-3 dB) fre-
quency over a range from 80 to 240 Hz. Below 80 Hz, the filter's slope is 12
dB/octave. At higher corner frequency settings, the slope is 6 dB/octave. The
purpose for this compound slope is to give additional roll-off at the 80 Hz
setting to reduce wind noise and low frequency rumble. The higher settings
can be used to counteract the proximity effect of directional microphones where a more gentle slope is
desired.
The 664's high-pass filter circuit is unique because of its placement before any electronic amplification.
Most mixers' high-pass filter circuits are placed after the microphone preamplifier, such that all of the
low-frequency signals get amplified. By virtue of the 664's circuit cutting the low-frequency signals
before amplification, higher headroom is achieved in the presence of signals with significant low-
frequency energy.
When possible, attempt to equalize at the sound source with microphone selection, placement, wind-
screens, and onboard microphone filtering. Many microphones have on-board high pass filters. Use
the high-pass filters on the 664 in conjunction with the microphone's filter to increase the filter's slope.
The filter can be removed from the circuit completely by rotating the high-pass filter control to the full
counter-clockwise (detented) position. The high-pass filter potentiometer can be adjusted easily and
then recessed to hide it from the mixing surface.
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