Looking at the Led Bar as a level display
A Led Bar usage
The incoming signal level, either analogue or digital, need to be monitored to ensure the levels match the DSP requirements. Likewise the MPX level is important in order to avoid over modulation. It is commonly thought that over modulation improves the station capture by enchroaching into the adjacent bands but this is wrong since over modulation results in more distortion. (The average IF bandwidth is optimise for the nominal modulatiopn level, hence IF filter distortion for higher levels). It is much more beneficial to introduce signal processing so increasing the average modulation level.
Driving a Led Bar Display
A led bar is one way of displaying the level of the incoming audio signals. Different colours can be used to give warning of excessive levels. The DSP calculates the number of led segments to be activated using a logarithmic curve and peak or average leveling.
A latch/driver is used to control the Led bar. Here a 16bit word is stored and held in the latch. The DSP treats the latch as a 32 bit memory bank with a single location so the MSx memory bank flag can be used tho select the latch without any need for address decoding. Since the bus can be up to 48bits wide, up to three latch and 48 Led can be controlled by a single memory write.
The dynamic range of the DSP is extremely large so it is easy to calculate the parameters for a -60dbm to + 4dbm display. By suitable signal processing different types of display can be designed, for example a non-linear logarithmic display(-60, -50, -40, -30, -20, -10, -4, -1, 0, +1, +4), something difficult to achieve by analogue means.
Different type of response, peak, average, rms with different attack and decay, VU simulation can easily be devised by changing the DSP algoritm.