HOW TO MEASURE AUDIO LOUDNESS
Connect your audio from any receiver or other audio source to the RCA connector at the
top of the meter. If you wish to measure a stereo signal you can measure each channel
separately or combine them with any common RCA combining connector. The meter terminates
the audio signal at 600 Ohms so that dBm reading can be recorded. Then depress the POWER
button and hold it on. The dBm reading will start out low and climb to the maximum reading in just
a few seconds. Before you release the button take note of the reading on the LCD meter. The
meter will continue to take readings as long as the button is pushed. When you release the button
the unit will turn off to conserve the battery.
The AVM stores and displays the highest RMS audio level received during the
measurement interval. The POWER button must be depressed and held each time a new
reading is to be taken. This storage mode causes the digital display to rapidly stabilize to the
maximum RMS reading in just a few seconds. A reference level should be established for audio
levels in any system, and by measuring your existing audio signal levels you can match your
levels to any fixed non adjustable level so that your channel to channel levels will be even.
One way to do this is to measure the audio levels you cannot adjust with the AVM
connected to the audio output of your TV monitor or cable set-top box. Average the readings
taken on the non-controlled channels, and then use that dBm level as a reference to set the
remainder of the channels. In this way all channels will be of equal loudness. The AVM measures
the true RMS value of the audio signal so it measures the actual loudness as perceived by a
listener.
Some program source levels are not as stable as a technician may want them to be. If
audio volume tests reveal that a given channel volume varies excessively, the loudness of that
channel can be completely stabilized by connecting an AUDIO LEVEL MASTER onto the
channel. Contact FM SYSTEMS for information regarding control of audio levels.
BAR GRAPH INDICATOR
The unit has a built-in bar graph indicator on the second line of the LCD meter. It operates
during the measurement period while the power button is depressed. This meter indicates the real
time RMS or power of the audio being measured. It main function is to indicate the condition of
the audio while a measurement is taking place. If the audio programming drops away or reduces
volume, you will see it on the LCD bar graph.
AUDIO LEVEL MEASUREMENT RANGE
The AVM can measure either balanced or unbalanced audio circuits at audio power levels
ranging from +20 dBm to -60 dBm. The meter will read either test tones or program audio in true
RMS, calibrated in dBm into 600 Ohm. When the input level of +20.9 dBm is exceeded the
display will flash a message indicating “Over Level” and if the input is less than – 60 dBm the LCD
display will flash the message “Under Level” to indicate an audio level below minimum
measurement level.
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