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OPTIMOD-PC
clip the audio.
For line-up, the studio engineer uses a calibration tone at a studio standard level,
commonly called line-up level, reference level, or operating level. Metering at the
studio is by a VU meter or PPM. As discussed above, the VU or PPM indication under-
indicates the true peak level. So the studio standardizes on a maximum program in-
dication on the meter that is lower than the clipping level, so those peaks that the
meter does not indicate will not be clipped. Line-up level is usually at this same
maximum meter indication.
In facilities that use VU meters, this level is usually at 0 VU, which corresponds to the
studio standard level, typically +4 dBu. For facilities using +4 dBu standard level, in-
stantaneous peaks can reach +18 dBu or higher (particularly if the operator over-
drives the mixer). OPTIMOD-PC's analog input clips at an instantaneous peak level of
+20 dBu, which provides 16 dB of headroom above a +4 dBu line-up level.
In facilities that use the BBC-standard PPM, maximum program level is usually PPM4
for music and PPM6 for speech. Line-up level is usually PPM4, which corresponds to
+4 dBu. Instantaneous peaks will reach +17 dBu or more on voice. In facilities that
use PPMs that indicate level directly in dBu, maximum program and line-up level is
often +6 dBu. Instantaneous peaks will reach +11 dBu or more.
Level and Subjective Loudness Metering in the 1101
The meters in the 1101 show peak input levels, the peak output modulation, and
subjective loudness.
•
Input levels and mixer output levels are displayed using a VU-type scale (0 to
–40dB), but the metering indicates absolute instantaneous peak (much faster
than a standard PPM or VU meter). The maximum digital word at the output of
the Processor Mixer corresponds to the 0 dB point on the 1101's input meter.
•
The output meter indicates the values of the digital samples at the output of the
1101's audio processing, not at its digital outputs. 0 dB on the output meter cor-
responds to the setting of each output level control except for the
For example, if the D
L
.
EVEL
indicates 0 dB, the peak level at the 1101's digital output is –3 dBfs. (This also ap-
plies to the wave outputs.)
0 dB on the meter also corresponds to the threshold of limiting of the 1101's
look-ahead peak limiters, which prevent the processed audio's level from increas-
ing beyond 0 dB.
If the output's sample rate is set to a rate other than 48 kHz and or
passed through a D/A converter, the peak level of the output may in-
crease by as much as 0.5 dB because the 6300's peak limiter is oversam-
pled at 192 kHz and not at infinite frequency. (See page 1-31).
control is set to –3 dBfs and the meter
O
IGITAL
UTPUT
INTRODUCTION
A
O
NALOG
UTPUT
1-7
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