User manual XTA G2

[. . . ] G2 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: Changing MODE between Gate and Expander; Enabling the sidechain LISTEN function; Ganging the two channels together in STEREO mode. ü The main meters show level, in dB, from the clipping point of the input of the unit just after the analogue to digital converter stage. [. . . ] The main use for an expander is to improve the dynamic range of an instrument or processing device. The dynamic range of any device is limited by two factors ­ it's minimum output, and it's maximum. It would seem reasonable to assume that the minimum output would be exactly zero, and that this level should be the same for all devices. Certainly, when the majority of instruments and devices are turned off (assuming they are powered in some way) they will all share a similar minimum output level. However, once on, it is the noise floor of the electronics within that determines the minimum output. A signal that is below the noise floor of any piece of equipment will not be resolved by that equipment. The maximum output level is largely determined by the power supply capabilities of the device. Many manufacturers (especially Far Eastern) tend to use power supplies with lower voltage rails, resulting in a poor drive capabilities and limited maximum output level. As the expander functions below the threshold, it is in the area of minimum output level that improvements can be made. Thinking laterally, the noise floor need not just refer to the electronically generated variety. Noise can be thought of as any "irregular fluctuations accompanying a transmitted signal but not relevant to it"1. This may now include other sources of noise such as: Hum due to poor power supply regulation or induced by an earth loop Background interference from lighting dimmers Stage noise picked up from a microphone or transmitted up a microphone stand Handling noise from a microphone Overspill when `miking-up' a drum kit 1 Concise Oxford English Dictionary 2000 Definition 3. G2 Operators Manual Page 15 An expander can be used to improve the noise floor under all these circumstances, by attenuating signals below a set threshold, thereby improving the clarity of the signal fed to it. One other area where expander can prove useful is in the control of feedback in a live situation. In the case of a vocal microphone, leaving it `open' all the time is likely to cause problems not only with the pick-up of extraneous noise, but allowing feedback paths to build up. Whilst the vocalist is actually using the microphone, their voice effectively stops all other sounds from entering. By attenuating the output from the microphone during pauses, the build up of feedback can be avoided. Consider again the signal burst shown below. Regions 1 and 3 are set to below the threshold of the expander, and will consequently be attenuated by an amount equating to the Ratio parameter. In region 2, the signal has risen to a level above the threshold, and so the expander will stop attenuating, and allow the signal to pass straight through. The difference between the attenuated signal when below the threshold and the original signal level (i. e. the degree of attenuation) is set by the Ratio. Continuing with the compressor analogy again ­ the ratio can be determined by considering the degree of attenuation required. [. . . ] Since the meter is deliberately set to show clipping 3dB early, this still provides 9dB of headroom before clipping occurs. It should be noted that the figure quoted for the maximum input level options is the clipping point for that option (not a safe operating level). Always ensure that this clipping point is no lower than that for the following equipment in the signal chain, and allow extra margin if equalisation sections are boosted. Grounding The Screen (shield) pins on all audio connectors are normally connected directly to the ground pin of the IEC mains inlet. [. . . ]