Sirus Live M416, Руководство пользователя, Страница: 34 / 45

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dB Tech Talk
P
i
= Input signal power
P
o
= Output signal power
dB = 10*log(P
o
/P
i
) = 10*log[(V
o
2
/R
o
)/(V
i
²/R
i
)
If input and output impedances R
i
and R
o
are the same, then:
dB = 20*log*(V
o
/V
i
)
dBm is defined as 1mW into
600
Ω
= 0,775V
dBu = 0775V
11.6. Using Inserts
The mixing console channel inserts operate at 0dBu/0.77V, the output inserts operate at -2dBu/0.62V.
In practice this makes little difference as long as the inserted equipment is intended for the line level
operation (-6/0.39V to +4dBu/1.23V). Simply set the gain through the device to unity (0dB) with the
bypass switched pressed (if available). With the effect switches in, use the console channel gain
control to make any further adjustment needed. This keeps the gain structure correct through the
channel signal path. With nothing plugged into the insert, the channel signal is routed through a
switching (‘normalling’) contact in the socket. As soon as a jack is plugged into the socket the contact
is opened and the signal path broken so that the external device can be patched in series with the
signal.
11.7. Polarity
Refers to the positive (+) and negative (-) wires of a loudspeaker or balanced audio connection. The
console input channels include POLARTITY switches which reverse the + and – input connections.
Some applications include correcting for reverse wired cables, correcting for microphone placement
problems, mixing two mics on a snare drum, one above the other below where diaphragms move in
opposite directions, and helping to reduce comb filtering effects as radio miked actors perform close to
each other. Polarity is sometimes labeled ‘phase’ on mixing consoles. Technically, ‘phase’ is not the
correct term as it implies a 180 degree time shift. Polarity simple reverses the wires. It does not affect
time. Before starting your mixing, check all the channel polarity switches are correctly set, normally up
(+).
11.8. Mixing the PA in mono or stereo?