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bhi DSP Noise Cancellation Products
for Radio and Voice Communications
www.bhi-ltd.com
NEDSP900 Manual/Datasheet
Main Features:
• Dual channel configurable Noise Suppression
• 30 dB AGC in channel 1 switchable
• Up to 30 dB maximum gain configurable input amplifiers
• Low power consumption (typ <5mA)
• Wide supply voltage range (3 to 20V)
• In‐and outputs RF protected with LC low pass filter
• Up to 40dB noise suppression
• Audio bandwidth 300Hz to 5KHz
Applications:
• Noise Cancelling Microphones
• Noise Suppression for radio voice communications
• Noise Cancelling in voice recognition to improve accuracy rates
• Intercoms
Issue:4
21-09-2016
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Summary of Contents for BHI NEDSP900
- Page 1 DSP Noise Cancellation Products for Radio and Voice Communications www.bhi-ltd.com NEDSP900 Manual/Datasheet Main Features: • Dual channel configurable Noise Suppression • 30 dB AGC in channel 1 switchable • Up to 30 dB maximum gain configurable input amplifiers • Low power consumption (typ <5mA) •...
- Page 2 NEDSP 900 User Manual 1. Introduction The NEDSP 900 is a dual channel audio Noise Suppression pcb module capable of handling a wide range of audio inputs and providing up to 40dB of noise suppression. The module operates on a single supply rain with on‐board voltage regulation and clock oscillator. It has low power consumption which makes it suitable for portable applications.
- Page 3 NEDSP 900 User Manual 3. Pin Designations (see fig1) From the annotated module outline fig1 on the previous page, the pattern of the pin-outs provides the user with good signal separation that can be continued easily on any board designed to carry the analogue and digital interface electronics.
- Page 4 NEDSP 900 User Manual It is recommended that, if the module is to be used with other interface circuitry be it buffering the analogue or digital signals, that further local supply suppression is used between Pins 1 and the nearest ground (Pin 2 is ground). This should be carried out in line with common engineering practices.
- Page 5 NEDSP 900 User Manual Note: Two important things to note about the audio channels, firstly the Gain setting only takes place when the module initialises. This means that any change in audio Gain setting can only be done before powering the module. Secondly, due to the design of the DSP device silicon, at 0dB audio gain selection, there may be up to 9dB of insertion loss between the module input and output.
- Page 6 NEDSP 900 User Manual The gain settings for Channel 2 are as follows: Module Pin 18 Module Pin 17 Gain (dB) Bit 1 Bit 0 Note: ‘1’ is pin left open or pulled up to 1.8V, ‘0’ is pin pulled to ground. 11.
- Page 7 This special function pin enables the noise cancellation to hold at the current value. When the pin is released (allowed to float to 1.8 Volts), the algorithm continues where it left off. For further information on this facility contact bhi Ltd. 15. Electrical Characteristics Absolute Maximum Ratings: Power Supply Voltage: +24V;...
- Page 8 NEDSP 900 User Manual 16. Background information on the DSP Noise Cancelling Automatic Gain control Automatic Gain control (AGC) selects the optimal input gain according to the input level. For low input signals the AGC Increases the gain up to 30dB, whereas the AGC only cares for the voice content.
- Page 9 17. Suggestions for Module Use The following section deals with the basic common practice requirements for integrating the NEDSP900 module into a system. Layout considerations The NEDSP 900 board is designed to provide a plug-in solution for noise cancellation. The board itself is designed to provide the best immunity from electrical noise and the best inter channel isolation, while giving the user plenty of latitude in way to incorporate the board into their system.
- Page 10 NEDSP 900 User Manual When using microphones for close in operation i.e. headset systems or desk microphones, it may be worth trying the modules AGC option – see section 9.0 of this manual. Higher level input signals Because the NEDSP has a wide range of gain settings, it is configurable for many types of input signal levels, however, if the module is to be used with speaker or headset output levels for instance an MP3 player or a mobile radio set, consideration should be given to the use of a potential divider network.
- Page 11 NEDSP 900 User Manual Output: The module output impedance is nominally 12 KOhm. This means that driving a low impedance balanced line will require buffering before using an unbalanced to balanced transformer. Alternatively, depending on the grounds within the system, it may be possible to use an unbalanced to balanced Op-Amp...
- Page 12 NEDSP 900 User Manual Typical NEDSP test circuit Note: the use of switches allows quick re-configuration of the NEDSP for testing. When the switches close the function is selected. The use of jumper pins or PCB solder patches are recommended for applications where the board is to be integrated into a larger system or where the configuration is likely to be fixed, but may need modifying.
- Page 13 Circuit c) – This is the simplest circuit and just provides a simple voltage divider action. Bearing in mind that the NEDSP900 input pins have a maximum of 1.8v voltage limit, you have to be careful with this. The resistors R3 and R4 need to be changed dependent on the control logic voltage being used (3.3v or 5v).
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Page 14: Contact Details
NEDSP 900 User Manual Contact details: bhi Ltd 22 Woolven Close Burgess Hill West Sussex RH15 9RR Tel: +44 (0)1444 870333 Fax: +44 (0)845 2179936 Email: sales@bhi-ltd.com Web: www.bhi-ltd.com Issue: 4...
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