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The Level Detector blocks calculate the input signal level, reading directly from the hardware in real time, and display the level graphically in meter displays. The Level Detector Designer block lets you define your own frequency bands and time constants for the display.
The level detector performs analysis only and does not modify the input signal. The signal at the output pin is identical to the input.
Use the On / Off button to enable or disable the display. The level detector will not function until the schematic design has been compiled and downloaded to the hardware and a USB communication channel is properly configured.
Note: The refresh rate of the display is approximately 10 Hz, while the green cross-bars track the maximum rms value with a slight delay. The display's performance is limited by your PC system and USB communication resources. Using multiple level detectors may degrade the responsiveness.
To use this block:
After selecting your default algorithm, there's an option to Grow it. The default block contains only one color bar, but when you grow your algorithm you can account for multiple frequency bands. The figure above right shows the Passthrough algorithm grown by 1.
To make the most of your level detector, it's important to understand the parameters in the designer window. Shown below is that window for a passthrough algorithm grown by 8. There are a 9 bands total, each with the option of choosing Filter type, Center Frequency, and Q or Bandwidth depending on filter type. (There also is an overall Time Constant and Decay value that can be set in dB/s to control the refresh time of the color display.)
Normally you should use double-precision: 56 bits for each calculation and 10 instructions per filter. Single-precision uses 28 bits for calculations and 6 instructions per filter, saving 3 data ram spaces over the double-precision algorithm. Note that single-precision should not be employed either for frequencies below 1/10 the sampling rate or for high-Q filters.