Gain Structure
Page 17
Peavey Electronics Corp
To fully understand how MediaMatrix
®
gain structure works, you should have a clear, high level view of how the Full-Scale
Input Sensitivity and Full-Scale Output Drive settings relate to the front panel and software-based audio meters.
First and foremost, it is important to understand what the levels mean. The Full-Scale Input Sensitivity and Full-Scale Output
Drive settings refer to separate analog circuits within the MM
™
-8802. These circuits are in addition to the fully adjustable ana-
log input and output gain stages. Both the Full-Scale Input Sensitivity and Full-Scale Output feature four user-definable set-
tings. These settings represent MAXIMUM (Full-Scale) levels, NOT nominal settings. Keep this in mind as we progress.
In a digital system, 0 dB indicates the “top” of the useable dynamic range, just below full-scale. For the inputs, full-scale indi-
cates the maximum level BEFORE converter clipping. On the front panel input meter, 0 dB has been calibrated to be <1 dB
below full-scale. Anything over this level is clipping, or in digital parlance, an “OVER”. Remember that the front panel input
meter is in the digital domain, just after the analog to digital (A/D) converter. The position of the Full-Scale Input Sensitivity
switch determines how much analog input signal is required to get the front panel input meter to read 0 dB. Or, in other
words, to get the A/D converter to full-scale maximum input level.
The MM-8802 typically provides greater than 105 dB of dynamic range. This is the range of 100%, clean audio above the pub-
lished noise floor, and below the threshold of converter clipping(Full-Scale). The adjustable sensitivity switches simply “shift”
this dynamic range upwards or downwards before the signal gets into the MediaMatrix DPU. This is done primarily to accom-
modate the connection of third party components and to match source output levels. The setting of the Full-Scale Input
Sensitivity will determine what level is required to drive the A/D converter to full-scale and illuminate the 0 dB front panel
input meter. For example, if +18 dBu is selected, then it will take +18 dBu of level to get to a 0 dB reading (full-scale A/D) on the
front panel input meter.
The setting in the Full-Scale Input Sensitivity dialog box will determine how the front panel input meters display audio levels
coming into the MM-8802. It is very important that these switches be set correctly. For example, if you know that the nomi-
nal levels of your system are going to be around 0 dBu, and you want to monitor peak levels 12 dB above that, then you will
want to use the +18 dBu setting for the Full-Scale Input Sensitivity. This will allow the front panel meter to d18 dBu at
the 0 dB LED. Your 12 dB headroom level in this case would show up at approximately -6 dB on the meter. In order to get the
maximum performance from the analog input stage of the MM-8802, it is recommended that your Full-Scale Input Sensitivity
settings be properly matched to the audio source and your headroom requirements.
What we are looking at so far is front panel metering. Remember this.....the setting of the Full-Scale Input Sensitivity switch
will always equal the 0 dB LED on the front panel input meter. This is the full-scale (maximum) level before A/D converter
clipping. So, how does this relate to the meters inside of MediaMatrix? Read on.....
Full-Scale Input Sensitivity set at +18 dBu
(Maximum level at A/D converter)
Analog Input +18 dBu = Full Scale
Full Scale = 0 dBu Meter
Front Panel Input Meter
Setting Full-Scale Input Sensitivity
