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1.4
DSP Noise cancellation.
The bhi DSP processes the incoming signal and then
differentiates the speech from the noise. The unwanted
noise and interference is then attenuated to leave only
the speech.
The following diagrams are taken from actual audio
signals and illustrate how the signal is being processed.
Figure 1. Noise cancellation.
Original signal.
Speech with a lot of
background noise
Processed speech.
Speech with reduced
noise
Speech Noise
Reduced noise
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NEDSP 1061
Audio out
10
0V
7
-
+
+V
R1
10K
R2
10K
Buffered
Audio out
Bias to 1/2
off supply voltage
or use dual polarity
power supply
Figure 12. Buffered output stage.
5.3
Driving a low impedance load.
If the target system loads the output of the DSP module
it may necessary to buffer the output. This can be
achieved with a single op amp.
10
7
9
NEDSP 1061
Audio out
Audio In
0V
+V
5
Audio out
Audio in
Relay
Contacts
Power
off/bypass
switch
Vin
Relay
Coil
Protection
Diode
Figure 13. Audio bypass.
5.4
Audio Bypass.
In safety critical applications a bypass should be included
to maintain communications in the unlikely event of the
NEDSP1061 or the power failing. The following circuit
uses a relay to route the audio signal. In the even of
power failure to the module the relay will de-energise
and connect the input to output. Also shown is a switch
to bypass the module manually.
