Sirus Live M416, Руководство пользователя

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The input channels provide PFL (pre-fads listen) so that each source can be checked using the meters
and headphones before you bring the fader up. You can even use PFL while the channel is muted to
prevent the signal reaching the house and monitor speakers until you have checked it and are ready.
All the main, aux and matrix outputs provide AFL (after-fade listen) so that you can check the exact
level leaving the console. Once again, the AFL switch gets its source before the output mute switch so
that you can check the signal before you send it to its destination. This can be very important when
you are feeding remote destinations such as broadcast and recording.
11.5. Decibel
The ‘Bell‘is the unit of sound level. Decibel is 1/10 Bell, a more conveniently sized unit. dB = 20*log
(V
o
/V
i
) where V
o
and V
i
are two signal voltages, in and out (ignoring the impedances). The dB is used
to express the relationship between two levels, chosen because of the logarithmic way our ears
respond to sound. The dB relates one level to another. For example, a preamp with a gain of 40dB
(100x) would produce an output of +10dBu for an input of -30dBu. Several audio standards exist to
relate a signal level to a known reference. Audio engineers need to deal with a variety of equipment
standards, for example, a -10dBV CD player plugged into a console with +4dBu/1,23V outputs
connected to a 0dBu input DSP speaker manager, or an operator using an SPL (sound pressure level)
meter to measure sound intensity.
dBu relative to 0,775Vms = professional standard
0dBu= 0,775V +4dBu = 1,228V
dBV relative to 1Vms = consumer audio standard
0dBV = 1V -10dBV = 316mV = -8dBu
dB-A Sound pressure with a filter contour to approximate the response of
the human ear. Three curves A, B, C exist for different loudness.
dBfs relative to signal maximum before clip (full scale)