C2 Quick Reference THINGS YOU NEED TO KNOW... ü BOLD MEANS HOLD! Any functions that would produce possible unexpected level changes at the outputs are protected by a `press and hold' action and printed in BOLD on the panel. These functions are: Switching AUTOmatic time constants on and off; Changing MODE between compressor and De-EQ; Enabling the sidechain LISTEN function; Ganging the two channels together in STEREO mode. ü The meters show level, in dB, from the clipping point of the unit ­ when the METER switch is set to `IN' the meters show level, in dB, from clipping the input converter. Set to `OUT' they show headroom available at the output ­ the DAC. ü When in De-EQ mode, the sidechain filter GAIN control will not function, as it is dynamically adjusted according to the threshold. ü The De-EQ mode LED always flashes when this mode is enabled. ü The Listen LED always flashes when Listen is enabled. Listen is automatically turned off if the unit is switched off and on ü When a channel is bypassed, all its metering and status LEDs will dim. All metering will continue to function. Page 2 C2 Operators Manual Contents C2 Quick Reference Important Safety Information Thanks Unpacking the C2 Introduction Features 2 4 5 5 6 6 Front Panel Familiarisation Rear Panel Connections Operating the C2 Switching the unit on and start-up procedure Press-and-hold Keys Minimum and maximum control positions 7 9 10 10 10 10 Compression ­ What It Is and What It Can Do What does a Compressor do? Why are Compressors necessary? How does a Compressor work? What makes the XTA Compressor different? 11 11 11 12 13 C2 Configurations Compressor Mode DE-Eq Mode 14 16 17 Sidechain Equalisation ­ How and When to Use it When would Sidechain EQ be useful? De-essing and de-popping. Maximising loudness without dulling the mix. How would sidechain EQ normally be implemented? 18 18 18 18 19 Why is the De-EQ mode so useful? Look Ahead Delay ­ Pre-emptive Action Setting the Attack and Release times The Compressor `Knee' Control. Using the AUTO system STEREO Linking 20 21 24 24 26 26 Operating Notes Operating Level Grounding 27 27 27 Specifications Warranty Options and Accessories C2 Operators Manual 28 29 29 Page 3 An example of this equipment has been tested and found to comply with the following European and international Standards for Electromagnetic Compatibility and Electrical Safety: Radiated Emissions (EU): RF Immunity (EU): Electrical Safety (EU): EN55013-1 (1996) EN55103-2 (1996) RF Immunity, ESD, Burst Transient, Surge, Dips &Dwells EN60065 (1993) Important Safety Information Do not remove Covers. No user serviceable parts inside, refer servicing to qualified service personnel. This equipment must be earthed. CAUTION RISK OF ELECTRIC SHOCK DO NOT OPEN DO NOT EXPOSE TO RAIN OR MOISTURE ATTENTION RISQUE DE CHOC ELECTRIQUE NE PAS ENLEVER NE PAS EXPOSER A LA PLUIE NI A L'HUMITE It should not be necessary to remove any protective earth or signal cable shield connections. Do not defeat the purpose of the polarized or grounding-type plug. A polarized plug has two blades with one wider than the other. A grounding type plug has two blades and a third grounding prong. The wider blade and the third prong are provided for your safety. When the provided plug does not fit into your outlet, consult an electrician for replacement of the obsolete outlet. Only use this equipment with an appropriate mains cord. In the USA the cord should comply with the requirements contained in the Standard for Cord Sets and Power Supply Cords, UL 817, be marked VW-1, and have an ampacity rating not less than the marked rating of the apparatus. Page 4 C2 Operators Manual Thanks Thank you for choosing the XTA C2 Dual Compressor for your application. Please spend a little time reading through this manual, so that you obtain the best possible performance from the unit. All XTA products are carefully designed and engineered for cutting-edge performance and world-class reliability. If you would like further information about this or any other XTA product, please contact us. We look forward to hearing from you in the near future. Unpacking the C2 After unpacking the unit, please check it carefully for any damage. If any is found, immediately notify the carrier concerned - you, the consignee, must instigate any claim. Please retain all packaging in case of future re-shipment. C2 Operators Manual Page 5 Introduction The C2 is a powerful DSP based audio dynamics processor, ideally suited for live sound applications, where it combines the accessibility and immediacy of a pure analogue design with the quality and accuracy of a digital design in a compact 1U unit. To achieve this, the C2 has an analogue control surface, following the `one control ­ one function' philosophy and a pure digital signal path, with 24-bit conversion, 40-bit internal processing and a professional 48kHz sampling rate. The C2 is also available with optional AES/EBU digital inputs and outputs. Features Look ahead attack available on the compressor for instantaneous control of transients Automatic time constants which are intelligently adjusted depending on the setting of other controls (namely the sidechain EQ frequency when in De-EQ mode) Sidechain EQ built-in for the compressor - switchable to lo/hi shelf and wide/narrow parametric, with variable stepped gain and high-resolution frequency adjustment. De-EQ mode - an extension of traditional De-Essing where the sidechain filter band not only affects the sensitivity of the compressor at certain frequencies, but also only compresses around those frequencies. De-Essing, and De-Popping, and any other band reduction in power as required. Digitally accurate metering with indication of closeness to compression threshold. Independent limiter section with metering. Stereo mode, where both channels are linked and track 100% accurately. AES/EBU Digital input and output interfaces are available as an option. Input and output balancing transformers are also available as an option. Page 6 C2 Operators Manual Front Panel Familiarisation Level Meter: Dependant on the setting of the `METER' switch, this will display the instantaneous available headroom, at either the input to the channel (analogue to digital converter) or the output from the channel, post limiter (digital to analogue converter). Active Key: Switches the entire channel on/off ­ LED illuminated when processing is active. All metering and status LEDs for the channel dim when the channel is bypassed. Threshold Control: Set the threshold at which compression will begin, from -30dBu to +22dBu (effectively off). Meter Key: Select what the level meter shows ­ either input headroom or output headroom. Still active even when the channel is bypassed. Ratio Control: Set the degree of compression to take place, once the signal exceeds the threshold, from 1:1 (no compression) to 16:1 (very heavy compression) Knee Key: Cycles through `Hard' knee (compression begins at the selected ratio as soon as the threshold is exceeded), `Medium' (compression is less pronounced just above threshold), and `Soft' knee (compression is least pronounced until well over threshold). Gain Reduction Meter: Green LEDs show 6dB and 3dB below the threshold of compression, with the yellow LED illuminating as the threshold is reached. The remaining red LEDs indicate progressively more gain reduction (compression) up to 24dB. AUTO Key: Enable the automatic time constants ­ in compressor mode these are preselected to provide transparent compression in as many situations as possible. In De-EQ mode, time constants track the filter frequency. Attack Control: Adjust how quickly compression starts after threshold is exceeded. The [-60uS] setting uses `look-ahead' delay to preempt the signal going over the threshold and so prevents any overshoot. Release Control: Adjust how quickly the gain reduction decreases once the signal drops below the threshold again. C2 Operators Manual Page 7 Make-up Gain Control: Apply extra gain to compensate for the compression gain reduction, helping to maintain the signal at its original level. MODE Key: Switch between normal compression mode, and DeEQ mode, where only the frequency band selected with the sidechain EQ is monitored and compressed. Sidechain EQ Type: Choose the shape of the sidechain filter moving between, from top to bottom, high shelf; narrow `Q' parametric; `wide `Q' parametric; low shelf. Sidechain EQ Frequency: Select the frequency range over which the sidechain filter will operate ­ this will be the centre frequency of the filter in parametric mode, or the corner frequency of the filter in shelf mode. LISTEN Key: Switches the output of the sidechain filter into the main signal path, so that the required range of frequencies may be more easily selected. LED flashes as a reminder that this is selected. Sidechain EQ Gain Key: Adjust the gain of the sidechain filter to sensitise or desensitise the compressor. +6/9/15 of gain is available, as well as 0db (off). Limiter Threshold Control: Set the threshold for the onset of limiting ­ effectively bypass the limiter by setting the threshold to +22dB. Limiter Activity Meter: Yellow LED illuminates when the threshold is reached, with the red LED indicating 4dB into limiting. STEREO Key: Enabling the `Stereo' mode will disable the right hand set of controls and force both channels to assume the parameter values of the left channel. The sidechains are also linked so that the two channels track perfectly, maintaining the stereo image. Page 8 C2 Operators Manual Rear Panel Connections Power Switch: turns the units mains supply off and on. Mains Fuse: located in a finger-proof holder adjacent to the mains inlet. A spare fuse is also located in this holder. Mains Inlet: connected via a standard IEC socket. Audio In-Out: 3 pin XLR sockets are provided for each channel. All are fully balanced, pin 2 hot, 3 cold, 1 screen. Always replace the fuse with the correct type and rating as shown on the rear panel legend. C2 Operators Manual Page 9 Operating the C2 Operation of the C2 is very straightforward, but there are a few points worth noting which, once understood, will make using the unit even easier. Switching the unit on and start-up procedure After plugging in the power and switching the power on suing the rear panel switch, confirmation is quickly given that all is well by various status LEDs illuminating almost immediately after power-up. These will include, as a minimum, METER (In/Out); MODE (COMP/De-EQ); and Sidechain EQ Type (Hi/Lo shelf etc.). The gain reduction will fully illuminate and, after the bypass relays disengage, begin to `count down' accompanied by the output level fading up to normal operating level. The entire process is complete when the input/output meters and gain reduction begin to operate normally. This whole start-up procedure only takes a few seconds. Press-and-hold Keys The legending on the front panel alerts the user to the fact that several keys require a `press and hold' action to initiate them. These keys relate to functions that could accidentally introduce large changes of level at the outputs, causing undesirable effects and possible damage. These keys have their function marked in BOLD (and a different font) to make it clear that they will only change state if the key is held in for a time. The keys in question are... LISTEN ­ switching the output to monitor the sidechain EQ signal (See page 15) MODE ­ switching between compressor mode and De-EQ mode (See page 16) AUTO ­ switching the automatic time constants on and off (See page 26) STEREO ­ linking the two channels together to operate in stereo (See page 26) Minimum and maximum control positions To ensure that the C2 is 100% accurate all of the time, and that what it says on the front panel is exactly what the unit is doing, it has been necessary to introduce `end-stops' on the controls. The extreme regions on each control marked with the curved line designate this entire region as relating to the parameter value shown. This is to compensate for the mechanical tolerances of the potentiometers. Page 10 C2 Operators Manual Compression ­ What It Is and What It Can Do What does a Compressor do? A compressor is designed to do as the name suggests ­ compress. What it compresses is the dynamic range of the audio fed to it. This means that it is used to control the level of the audio in such a way as to limit its maximum value, but in a gradual fashion. As you might imagine, it would be possible to prevent the level from ever going over a maximum threshold in a very severe manner ­ generally this type of action as known as `Limiting', and is the responsibility of the Limiter Module also in the C2. The method by which a compressor limits the maximum level is performed in a more gradual way so as to gently control the dynamic range, rather than dramatically `cap ...