Blue 330
Isomorphic Stereo Mastering Compressor and Limiter
The controls are described section by section starting with the two large PPM meters are centrally
mounted and controlled by the five meter selection switches in the upper right corner of the module
- the signal displayed may be selected from one of four sources, the input, the key input, the total
gain change being applied by the compressor section and the output signal. To assist in the reading
of signal peaks there is a higher level range showing from -4dB to +20dB, this is selected by the
+16dB switch.
The upper left houses a switch to select the key input. The sidechain is fed from the key input
when this switch is lit. There is also an overload indicator which will flash when the peak of any
signal reaches or e20dB, which is 6dB prior to the onset of clipping.
Input Gain control is by one master switched rotary switch in 1dB steps over the range ±10dB for
both channels simultaneously. There are separate channel trims, continuously variable ±1dB,
which are not in-circuit unless selected by the adjacent switches.
Make-Up Gain is arranged in the same manner as the Input Gain, except the master rotary provides
for up to 22dB of make-up gain. The sensitivity is the same as the Input Gain at 1dB per step,
thus it is easy to contra-rotate the two large master gain controls thus effectively changing the
threshold points whilst keeping the overall level through the module constant. Both the Input Gain
and the Make-up Gain controls have the same sensitivity, therefore it is possible to contra-rotate
both controls to adjust the overall sensitivity of the Compressor and Limiter functions whilst
maintaining the same overall gain
The Compressor section has a Compressor In switch , a dual range Threshold switch calibrated
in1dB steps and separate rotary switched controls for Ratio , Attack and Release .
The Limiter has its own In switch, a separate switched rotary Threshold, again 1dB per step and a
large indicator which lights whenever the limiter is called to operate.
Although the Compressor and Limiter have separate controls , they may be used together, in which
case the Compressor function comes first , followed by the Limiter , which will act on the
compressed signal, limiting only the selected peaks remaining after the compressor action.
The left side of the module has an illuminated power supply switch and a Master In switch. This
Master In is an overall In switch to allow simple comparison between direct and processed signals
and has two modes :
1) push and hold - the switch will have a momentary action and will cancel upon release
2) a quick press and release will cause the switch to latch on , a further quick press will dis-engage it
.
