User manual

Page 3
2. Introduction
The bhi DESKTOP speaker is a microprocessor controlled amplified DSP noise cancelling
base station speaker that removes noise and interference to improve the quality of speech
in noisy radio and voice communications. It is suitable for use in base station applications
where background noise and interference mean that you cannot clearly hear what is being
said. The speaker will enable the user to listen and concentrate “stress-free”. Suitable
applications where the speaker will be of great benefit are: amateur radio, two-way radios,
HF radios, marine communications, scanners, taxi base stations etc. The DESKTOP
speaker incorporates unique Digital Signal Processing technology (DSP) to remove the
unwanted background noise and interference. The DESKTOP speaker has separate line
level and speaker level inputs allowing it to be used with a wide range of radio and audio
equipment including SDR radios. There is also a 3.5mm headphone socket on the side of
the speaker and either mono or stereo headphones can be used.
The DESKTOP speaker comprises a 4” bass driver and a 1” tweeter unit, with an amplified
bhi DSP noise cancelling unit capable of producing up to 10Watts audio (peak). The
speaker requires an audio input signal of between 160mV and 1.6mV peak-to-peak for line
level, and 350mV and 3.5V peak-to-peak for speaker level input, and requires a DC power
supply of between 12 and 18 Volts (2.5A peak). The unit is supplied with a quality
moulded 3.5mm mono jack plug lead terminated with 4mm banana plugs, a 2.1mm fused
DC power lead and a user manual.
Note: The speaker is mainly designed for speech signals and is not really suitable for
music.
3. bhi DSP Noise Cancellation
The bhi DSP processes the incoming signal and 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
processed.
Original signal.
Speech with a lot of background noise
Processed speech.
Speech with reduced noise