The Downmix Matrix
The outputs of the 6-channel buss amp feed the inputs of the stereo downmix matrix. This section converts the 5.1 surround signal into a stereo signal. The left surround-channel SL is added to the front-channel L and the right surround-channel SR is added to the right front channel. The level of the SL and SR channels can be adjusted by the pot S > F in a range from 0 to - 6 dB. The 3 dB center detent is calibrated. The center channel is mixed into both the L and R front channels. The level is controlled by a second pot with the same range from 0 to - 6 dB and a calibrated center position of - 3 dB. The LFE channel is added to both front channels like the center channel, however, this channel passes an internal low-pass filter with a cut off frequency of 80 Hz. The level of the LFE is fixed at - 6 dB, but a general level control with +/- 10 dB control range allows correction of this channel.

If the Stereo Mode switch is pressed, the output of the downmix matrix is switched to the front left and front right channels. All the other channels are muted.

This principle is favorable for several reasons. Since the matrix is pre insert, the use of stereo processing devices is possible without problems and without the need to consider about the settings of the 5.1 panoramic sections. If the stereo matrix is installed post the insert, only the left and right front channels would be processed by a stereo device. In addition this principle avoids the need of complicated and expensive switching facilities in the channels. The panoramic section always operates in surround sound mode and the downmix matrix switches the console to stereo mode or is used for checking the stereo compatibily. As the matrix adds all the 6 channels, the regulation characteristics of the LCR-Pan, which is crucial for stereo operation, is not different from the operation of a normal stereo pan. A minor change in the characteristic around the center position is caused by the setting of the channel's divergence control. A setting of this pot near to 1 (all to the right) enhances the precision of the adjustment around the center position.

Since there is still no standard for the level relation between the LFE channel and the other 5 channels, it is necessary to have an independend control for this level with an appropriate range of +/- 10 dB.

The switches OSC and TB enable the oscialltor group bus and the talkback group bus. These functions require the installation of the optional talkback and oscillator module.

The master fader section is a 6-channel VCA unit that is controlled by a 100 mm slider fader. The maximum gain of the fader section is 10 dB.

The output drivers of the master module are electronically balanced. If the module is switched to stereo mode, the surround channels, the center channel and the LFE channel are muted.

Aux and Cue Master Section
The master amplifiers for Aux 1, Aux 2 and the stereo Cue send are installed in this unit. Every master section has a rotary pot for the master level, a cut switch that mutes the output and an AFL switch to control the master output. An internal jumper determines if this switch operates in AFL (default) or PFL switch mode. The TB and OSC switches enable the talkback to aux line and the oscillator to aux line. These functions are avaiable if the optional talkback and oscillator module is installed. The cue master section has an additional Mono switch that inserts a standard matrix into the cue output. The mono signal drives both of the cue outputs.

VCA Group Masters
The SCR51 surround console comes with 4 combined VCA and Cut-Groups that can control the main mono, stereo and 5.1 input module faders. 2 of the VCA masters are installed in the S3-MS5 master module. There is one 100 mm VCA fader and a cut switch per group. The groups operate as vca groups unless the cut switch is pressed. A group cut activates the cut of the associated channels and overrides the fader settings.