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3.0 STANDARD FILTER CONFIGURATIONS
3.1 Selecting the Correct Filter Mode
The filters in the standard MicroDAC IV are optimized for noise cancellation to increase voice
intelligibility. Simple noises (e.g., tones, hum) are generally greatly attenuated. However, more
complex noises (e.g., ambient restaurant noise, bar noise) may not be as effectively attenuated, but
should be somewhat reduced.
The
MODE
switch setting determines the type of filtering based upon the configuration programmed
into the MicroDAC IV. When in the
BYPASS
mode, the MicroDAC IV simply transmits any audio
applied to the
ANALOG INPUT
connector directly through to the
ANALOG OUTPUT
connector,
bypassing the audio filters.
The three standard filter configurations correspond to the first three positions of the
MODE
switch;
the remaining positions are programmable by the Windows software. The standard filters are one-
channel mono (
1CH
), two-channel mono (
2CH
), amd one-channel stereo (
1CH
•
ST
).
The
1CH
filter does an excellent job of reducing simple time-correlated noises, such as tones, hums,
and buzzes from a monaural signal. It also does an excellent job of reducing echoes and
reverberations. Similarly, the
1CH
•
ST
filter removes tones, hums, buzzes, and echoes from a stereo
signal, except that the filters’ capability is spread across two signals, versus just one in the
1CH
case.
The
2CH
filter is used primarily for live radio/TV removal. If the incoming audio from a microphone is
corrupted by interfering audio from a radio or television, a second radio/TV tuned to the same
channel can be used as a cancellation reference for reducing the interfering audio and revealing the
desired conversation. Simply connect the audio output from the second radio/TV to the
RIGHT
(REF)
input, adjust the levels, and the cancellation will be performed automatically.
3.2 Hints For Effectively Using The MicroDAC IV’s Filtering Capabilities
First, it is vital that the microphone installation and/or source material be prepared as carefully
as possible. For example, if the source audio is from a tape recorder and the microphone was
placed beside a loud air conditioner and the target voices are 40 feet away, it is doubtful any
recoverable voice was recorded onto the tape, especially if the recorder used an automatic
level control mechanism (While this sounds like an unusual example, it does happen
frequently.) Also, make sure the heads are clean and properly aligned on the playback
machine, to allow maximum recorded signal to be available to the signal processor.
Second, keep the input levels in the green to yellow zone at all times. Increasing the input level
into the red zone could create distortion that will hinder the MicroDAC IV’s filtering capabilities.
Third, if the filtered output of the MicroDAC IV is to be recorded, make sure that the recording
machine’s heads are clean and that the mechanism is properly lubricated and in good working
order.
