USL CM-8E - Manual (Page 11)

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amplifier with an input resistance of greater than 600k. These differential amplifiers drive the
audio switching matrix and the band/channel level detection circuitry. Front panel and web
browser buttons select which channels and bands drive the front panel speaker, the front panel
VU indicator, the web stream, and the web copy of the front panel VU indicator. All bands of all
channels are measured continuously and sent to the web server for display on a remote web
browser.
Band and channel audio from the audio switching matrix is sent to a digital signal processor
(DSP) where the audio is digitized. The digitized audio level is measured to drive the front panel
VU indicator and its web browser copy. The digital audio is then split to drive two compressors,
one for the web stream and one for the front panel speaker. These compressors reduce the
dynamic range of the audio to make it more suitable for the front panel speaker and the web
stream. The speaker audio is also passed through an equalizer to compensate for the frequency
response of the speaker itself. Finally, the speaker audio passes through a level control, then
digital to analog conversion to drive the front panel speaker.
The output of the web stream compressor is sent to the web server. The web server streams
the selected audio at 44.1k samples per second monaural as either IMA ADPCM (4 bits per
sample for a total of 176kbps) or PCM (16 bits per sample for a total of 706kbps). The web
server also sends the measured levels of each band and channel to the web browser to display
them on a single bar graph.