Sound Devices 633 - Manual (Page 23)

AES digital signal carries two channels of audio. When the source of Input 1 is set to AES42 or AES3,
the first channel of the AES signal is present on Input 1 and the second channel of the AES signal is
available on Input 2. Selecting AES42 or AES3 source for Input 2 will connect to the second channel
of the AES signal (plugged into Input 1) and disable input 2’s XLR-3F connection.
The 633’s digital inputs are sample rate converted to the internal recorder’s sample rate.
High-pass Filter
Each input channel has an adjustable High-pass Filter controlled by pressing the Select Encoder from
the input’s Input Settings Screen, rotating the Select Encoder to adjust the frequency, then pressing
the Select Encoder again. To disable an input’s High-pass Filter, rotate counter-clockwise until the
value HPF Off is shown.
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,
because audio information below 100 Hz is rarely used, especially for speech reproduction.
The 633’s High-pass Filter circuit features an adjustable corner (-3 dB) frequency 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 counter-
act the proximity effect of directional microphones where a more gentle slope is desired.
The 633’s High-pass Filter circuit is unique because of its placement before any electronic amplifica-
tion. 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 633’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 633 in conjunction with the microphone’s filter to increase the filter’s
slope.
When Setup Menu option RECORDER > Sample Rate is set to 192k, the High-pass Filter is not ad-
justable. The available options in this mode are Off and 50Hz.
Polarity
Change the polarity of Input 2 from the Input Settings Screen ( See “Input Settings Screen”, page 11 ).
In
puts
633 User Guide and Technical Information
17