Bose Personalized Amplification System Troubleshooting Manual page 23

THEORY OF OPERATION
The MCU needs to transfer the clip state information to the remote control. The communication
protocol adopts hardware UART. The communication rate is 9600bps, Data is sent according to
MIDI protocol: MIDI channel number | MIDI parameter type | MIDI parameter value. DSP will
transfer a frame data every 100ms, and every sending will take about 3.5ms.
Relay of Remote information to the Power Stand DSP. The remote needs to transfer the
Ch1EQHi, Ch2EQHi, Ch1EQMi, Ch2EQMi, Ch1EQLo, Ch2EQLo, Ch1Volume, Ch1Volume, and
MasterVolume information to the power stand MCU PCB. The communication adopts hardware
UART. The communication rate is 9600bps, Data is sent according to the MIDI protocol: MIDI
channel number | MIDI parameter type | MIDI parameter value. DSP will transfer a frame data
every 100ms, and every sending will take about 30ms.
The power stand MCU PCB needs to transfer the Ch1EQHi, Ch2EQHi, Ch1EQMi, Ch2EQMi,
Ch1EQLo, Ch2EQLo, Ch1Volume, Ch1Volume, MasterVolume, Ch1Preset, Ch2Preset,
BassChk, and CheckSum information to the DSP. The communication adopts software simula-
tion UART, with two I/O pins as RX and TX. Communication rate is 4800bps, add start bit and
stop, so every sending byte has 10 bits. Data is sent according to frame format: every data |
check sum. DSP will transfer a frame every 100ms, and every sending will take about 30ms.
1.9 Software and User Interface
The Bose ® Personalized Amplification System™ family of products has a simple user interface
which is mostly implemented in software. In this chapter we describe how most of the functions
are implemented.
1.9.1 Gain Staging
Gain staging is the process of properly adjusting the gain of the system. The goal is to set the
gains as high as possible (to optimized signal/noise) without overdriving or clipping any elec-
tronic components. In contrast to home-audio products, musical instrument and microphones
have a large variation of output gains and gain staging is typically required.
On Channel 1 and 2, the user needs to set the trim control on the power stand so that the
overload LED just turns red for the loudest anticipated input signals and then back up a little.
This is done purely in analog and the goal is to not overload the preamplifier.
Next the user should adjust the channel volume on the remote so that the LED on the remote
does not turn red. The LEDs are calibrated so that for sine wave input, nothing connected to the
insert loop, and the channel volume at the 12 o'clock setting both LEDs turn red at the same
level.
1.9.2 Channel Volume
The microcontroller polls the remote in regular intervals, about 10 times per second. The
microcontroller then maps the settings to a range from -40 to 0 dB and programs the volume
control chip U302 through its digital control interface. The volume control should span a range of
40 dB with a linear (in dB) range from -30dB to -10dB from all the way down to 12 o'clock and a
range from -10dB to 0dB for 12 o'clock to "all the way up" setting.
1.9.3 Tone Controls
The microcontroller polls the remote in regular intervals. The microcontroller transfers the tone
control settings to the DSP which implements them for each channel as shown in Figure 11.
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