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1605C Noise Operated Automatic Level Adjustment Device

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The mixer also contains two auxiliary input channels for high-impedance line or tape sources. These channels have independent monitor sends, pan pots, and slide faders.

1605C NOISE-OPERATED
AUTOMATIC LEVEL
ADJUSTMENT DEVICE®

DESCRIPTION


The 1605C Noise-Operated Automatic Level Adjustment Device (NOALA) is a system for automatically adjusting the level of paging and/or background music to compensate for variations in ambient noise level of an environment in which loudspeakers are installed.
NOALA is inserted between the line level program source and the system power amplifier, where it functions as a noise-control, variablegain element. The 70-volt output line of the power amplifier is routed through NOALA where the line is opened by a control relay. The relay allows one side of a 70-volt line to be open in the absence of paging or music, and senses the noise voltage being generated by the speaker system. This noise voltage is amplified and rectified to produce a dc control voltage proportionate to the noise level. When paging or music is present, a quench circuit disables the sample and hold circuit, maintaining a dc control voltage representative of the last noise sample.
A music channel permits mixing of both music and paging through the automatic gain control feature of NOALA. An interruption of either paging or music will cause NOALA to sense the ambient noise and correct the gain accordingly. A music pre/post switch allows the music channel to bypass the automatic gain feature. If the music is of a continuous nature which does not permit sufficient time for noise sampling, NOALA may be used in a pre-page sample mode where an external switching line, operating from the press-to-talk paging microphone, quenches the music channel, allowing the NOALA to switch to a noise-sensing mode. The noise is sampled for 3 seconds, during which voice will override the sample mode. NOALA then switches the paging channel to active and indicates on a page-ready lamp at the paging microphone location that the operator may
proceed with the message.

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