Page 7
3.0 Installation
The NEDSP1901 module is inserted into the path of the noisy audio. Adjusting the Input and Output
level controls allows the module to appear transparent to the audio signal level.
Figure5. General Audio signal flow with 1901 module installed
The NEDSP1901 requires a minimum signal level of 10mV rms or greater for optimum performance.
Signals lower than this may be used but the noise cancellation performance will be degraded as the
signal level drops. If the module is to be used with low level microphones, the signal will require
pre-amplification. The Output level control may be used to attenuate the signal back down to the
original signal level.
4.0 Functions
4.1 Noise Reduction Levels
8 Levels of noise reduction are available. Noise and tone reduction is shown in the table below:
Notes:
1.
When processing signals with high levels of noise using the higher levels of Noise reduction,
the processed signal may sound a little strange. This quite normal with this type of signal.
2.
Due to the adaptive nature of the noise cancellation algorithm, a small delay may be
experienced when the audio signal varies in the noise. For optimum performance the
module should be provided with a constant signal, for example if the module is installed into
a system employing a push to talk system, then the module should be inserted in the audio
path before any switching or muting. Thus, the signal will always be available for the
module to adapt to.
Level
Tone Reduction
White Noise
Reduction
1
4dB
8dB
2
5dB
12dB
3
6dB
16dB
4
8dB
20dB
5
16dB
25dB
6
21dB
30dB
7
25dB
35dB
8
65dB
40dB
