BHI NEDSP1901-PCB User manual

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Copyright: This publication, including all photographs and illustrations is protected under international
copyright laws, with all rights reserved. Neither this manual, nor any of the material within, may be
copied or reproduced without the written consent of bhi Ltd.
Disclaimer: The information in this document is subject to change without notice. bhi Ltd. makes no
representations or warranties with respect to the contents hereof and specifically disclaims any implied
warranties of merchantability or fitness for any particular purpose. Furthermore, bhi Ltd. reserves the
right to revise this publication and to make changes from time to time in the content hereof without
obligation of bhi Ltd. to notify any person of such revision or changes.
1. Introduction
The NEDSP1901-PCB module is an audio DSP noise cancelling module that is used to clean up noisy
speech signals to give improved speech clarity in noisy conditions. The 1901 module is pin for pin
replacement module for the discontinued NEDSP1061-PCB module. It operates with a similar
specification but incorporates the latest bhi DSP noise cancelling technology and maintains virtually the
same physical dimensions as the NEDSP1061-PCB.
DSP side of PCB Rear side of pcb
1.1 NEDSP 1901 Module Features:
Fully adaptive to changing noise environments
Input and output level controls
Virtually no distortion to speech signals
Up to 40 dB noise reduction in 8 selectable levels
Audio bandwidth 300Hz to 5KHz
Noise Reduction may be preset or remotely set during operation.
7 to 18 Volt supply range
Approximately 10 dB of signal gain with the ability to drive impedances of less than 1KOhm.
Wide range of connection possibilities
Mounting holes
NEDSP1901-PCB Draft User Manual

1.2 Limitations
This module is designed to pass speech. Other signals such as data, music and morse (CW) will, to
some degree pass through, but the integrity of these signals cannot be guaranteed.
Like the 1061 it is designed to be placed in a low level audio path (up to 1V p-p) only, although there
is a level adjustment on the module which will require adjustment. The output will not drive a
loudspeaker or other high power load.
1.3 Module connection and Mounting
Connections to the module are made by a row of 10 plated through holes to one end which form PL2.
The holes are on a 2.54 mm (0.1”) pitch which allow the use of Straight or Right angle pin headers or
direct wiring. This makes a flexible connection arrangement and allows the using to be mounted either
vertically or horizontally, plugged in or soldered directly to the target system.
Connections to the module are via PL2, as
given in the table opposite.
Pin No
Name
Description
1
N0
BCD lsb noise reduction bit 0
2
N1
BCD noise reduction bit 1
3
N2
BCD msb noise reduction bit 2
4
N/C
Do Not Connect
5
Vin
Vin Supply Voltage (5V to 20 V)
6
N/C
Do Not Connect
7
0v
0V connection
8
Noff
Noise Reduction On/Off pin
9
In
Audio Input
10
Out
Audio Output
PL2
Input Level adjustment
Output Level adjustment

Whichever method of connection is used, ensure that the PCB is supported by using at least 2 of the
M2.5 mounting holes to be found at the corners of the board. It’s recommended that Nylon Securing
hardware is used to ensure that accidental shorts are avoided due to the fine nature of this PCB.
The Audio signal into the module is capacitor coupled to prevent DC offsets being affected.
An on-board voltage regulator allows the module to be used with a wide range of input voltages, but to
keep the power dissipation (and heat) down, it is advisable to use as low as possible supply voltage. The
power supply input is reverse polarity protected.
1.4 DSP Noise Reduction
The NEDSP1901 processes the incoming signal and uses known speech and noise patterns to
differentiate the speech from the noise. The unwanted noise and interference is then attenuated to
leave only speech.
The module has the facility to be pre-set or adjusted
during operation. Digital inputs control the
functions. These incorporate internal pull-up
resistors so they can be left floating when not in
use.
The diagrams in Figure 1 (opposite) are taken from
actual audio signals and illustrate how the signal is
being processed.
Figure 1 –Noise Cancellation
2.0 Module Description
2.3 Pin Functions
The basic operation of the NEDSP pins are described below. More details may be found later in this
manual.
Pins 1-3 DSP Filter level set -These pins allow remote setting of the noise cancellation level. If these pins
are used, then ensure that the appropriate on-board pre-set solder jumpers are removed (JP1 –JP3).
Pin 5 Supply Voltage - Supply voltage 5 V to 15 V DC

Pin 7 0V - This is the 0V pin and acts as a Star Point for all Audio and Power Grounds.
Pin 8 Noise Reduction On/Off - Connecting this pin to 0V inhibits the noise cancellation. Leave this pin
floating or tie it to +3.3 V to enable noise cancellation.
Pin 9 Audio Input - Audio Signal to be processed
Pin 10 Audio Output - DSP Processed signal from the module.
For optimum performance, keep all leads as short as possible. Use screened leads for the audio signal
and make sure that the 0V pin is grounded correctly with all signal grounds being reference to this pin.
2.4 Controls
The audio level control potentiometers VR2 (Audi Out) and VR1 (Audio in) provide adjustment to audio
levels entering and leaving the module. Both controls are pre-set at the factory such that a 1V p-p input
provides a 1V p-p output with the Noise Reduction disabled.
To set the Input Level correctly, adjust VR1 until the ‘Overload’ indicator (LED1) just illuminates. Then
back off the potentiometer until the LED extinguishes. Turning the potentiometers clockwise increases
the levels.
2.5 Electrical Characteristics
Output impedance: 1k Ohms typical
Input impedance: 7.5k Ohms typical
Analogue Characteristics
Parameter
Description
Min.
Typ.
Max.
Units
Vin
Supply Voltage
5
8
15
V
Iin
Supply Current
15
20
mA
In
Audio Input Signal
20
500
mV (rms)
Out
Audio Output Signal
1000
Digital Characteristics
Parameter
Description
Min.
Typ.
Max.
Units
VHigh
High Level Input Voltage
-
3.3
5
V
VLow
Low level Input Voltage
0.8
-
-
V
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. Connections to the pcb
can be made via PL2 using a standard Harwin type 0.1” pitch pin header.
The NEDSP1901 requires a minimum signal level of 50mV 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. The amount of noise and tone reduction is shown in the table
below:
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
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. Thus the signal will always be available for the module to adapt to.
4.2 Setting different filter levels
The levels are set by applying a BCD code to three solder jumpers on the underside of the module.
The module can be controlled with a microcontroller. As the DSP employs internal pull-ups, it is not
necessary to drive the microcontroller pins high, they can be placed in a high impedance state.

4.3 Remote setting of DSP filter level
Remote setting of the DSP level may be achieved through the PCB connections at PL2, this allows the
filter level to be changed during operation. If the remote DSP settings are to be used, ensure that the
solder jumpers are removed from NS0 through NS2 as shown below:
To set the DSP level remotely, connect the pins N0, N1 and N2 (PL2 pins 1, 2 and 3 respectively) as
shown on the following page.
Level
N2
N1
N0
1
0 V
0 V
0 V
2
0 V
0 V
+3.3 V
3
0 V
+3.3 V
0 V
4
0 V
+3.3 V
+3.3 V
5
+3.3 V
0 V
0 V
6
+3.3 V
0 V
+3.3 V
7
+3.3 V
+3.3 V
0 V
8
+3.3 V
+3.3 V
+3.3 V
The DSP Module has internal pull-ups on its inputs, so any cell in the table containing +3.3 V may be
taken up to or left open circuit.
4.4 Setting the Noise Reduction Level using the On-board Jumpers
The on-board Noise reduction selection jumper selectors are located on the underside of the Module as
shown below. These jumpers are actually PCB pads that should be linked using a solder bridge. Caution
should be used when carrying out this operation to ensure that other components and connections are
not bridged as this could cause the module to malfunction or even fail.
Above - underside of the NEDSP 1901 module showing the on-board PCB pad jumpers
NS0
NS1
NS2

The Noise reduction Levels are selected as shown in the
table opposite.
NOTE: Due to the logic inversion used within the module,
External Control pins 1, 2 and 3 of PL2 should be linked to
pin 7 of PL2.
4.5 Noise Reduction On/Off
The module has the provision for remotely enabling and disabling the noise reduction, while in
operation. The default setting for the module is noise reduction ON. This may be switched by the use of
the noise cancellation on/off pin (PL2 pin 8). To inhibit noise reduction, connect this pin to 0V. To
enable noise cancellation leave the pin unconnected.
Level
NS2
NS1
NS0
1
Open
Open
Open
2
Open
Open
Linked
3
Open
Linked
Open
4
Open
Linked
Linked
5
Linked
Open
Open
6
Linked
Open
Linked
7
Linked
Linked
Open
8
Linked
Linked
Linked

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