10
3.2 Hints For Using The PicoDAC Adaptive Filter:
•
First, it is vital that the
source material is prepared as carefully as possible
.
No amount of filtering will enable the operator to hear a voice that is not there.
For example, if the source audio is from a tape recorder and the microphone is
beside a loud air conditioner and the target voices are 40 feet away, it is doubtful
any recoverable voice was recorded on the tape. (While this sounds like an
unusual example - it does happen occasionally.) Also, if a tape player is used,
make sure the heads are clean.
•
Next,
select the appropriate bandwidth
. The best results for adaptive filtering are
achieved by matching the bandwidth of the PicoDAC to the bandwidth of the
recorded voice.
Table 2, below, can help select the best bandwidth.
For example, if the input source is a telephone line that typically has a bandwidth of
3.4 kHz, use filters 0 and 1. Since the telephone line does not have any voice
energy above 3.4 kHz, setting the PicoDAC for a higher bandwidth
may
elevate hiss
noise above 3 kHz in the output audio. This added noise can make understanding
the voice more difficult.
Typical Equipment
Bandwidth (kHz)
FILTER
Settings
Telephone Line
3.4
0, 1
Microcassette Recorder, Body Transmitter
5.0
2, 3, 4, 5
Standard Cassette, Nagra Recorder
7.5
6, 7, 8, 9
Table 2: Filter Bandwidths
•
Lastly, listen to the unfiltered input and
select the appropriate filter size
. While
selecting too large a filter will reduce simple noises, the remaining voice can
become sterile or unnatural sounding. On the other hand, selecting too small a filter
size may have less effect on complex noises. Select the initial filter size by referring
to the table below, but feel free to experiment with the other filters and listen for the
best results.
