PreSonus FireBox - Manual (Page 17)

3 CONTROLS AND CONNECTIONS
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NOTE: Active instruments are those that have an internal preamp or a line level
output. Active instruments should be plugged into a line input (3 or 4) rather
than into an instrument input. In other words, don’t plug an active instrument
into the combo jacks on channels 1 or 2.
3. Input Gain/Trim Control. This knob provides the following gain structure for
each channel:
Microphone Input XLR: 45dB of variable gain (+14dB to +55dB)
Instrument HiZ Input TS ¼” (channels 1 and 2 only): 45dB variable
gain (+8dB to +50dB)
Clip Indicator. The clip indicator will light up if your input signal from the XLR (Mic) or
¼” (line) reaches +18dBu (0dBfs). At this level, your mic preamp/line trim signal may
not exhibit signs of clipping such as distortion. However, this level would cause the A/D
(analog to digital) converters to clip. Therefore it is highly recommended that you do
not allow your converters to clip (the clip indicators to light up) as the sound quality
would not be desirable.
4. Main Level. This knob allows control over the output level for the MAIN CR
OUTPUT 1 and 2 on the back of the FIREBOX. It has a range of -80db to +10dB.
5. Headphone Symbol and ¼” Jack. This is where you connect your headphones.
6. Phones. The Phones knob controls the amount of volume going to the headphone
output on the front of the unit. Notice the volume indicator goes to 11 (loud). Use this
setting with caution.
7. Red-Blue Power/Sync Light. This light is a clock (sync) indicator. It lets you know if
your unit is receiving word clock correctly. Word clock is the manner by which digital
devices sync frame rates. Proper word clock sync prevents digital devices from having
pops, clicks, or distortion in the audio signal (due to mismatched digital audio
transmission).
Blue – solid sync
Red – sync not present.
Flashing Red and Blue – external sync not present