FRONT OF HOUSE
IT ’ S NOT GAIN ; IT ’ S DIGITAL TRIM | Kent Morris
Analog mixing consoles had a potentiometer at the top of each input channel strip labeled “ gain ” and its purpose was to increase the level in the circuit within the preamp until the input was appropriate for the console to utilize fully without clipping . Digital consoles also have gain on each channel , but they also have a separate control marked “ trim ”. The difference is gain controls amplitude in the analog domain before the ADC ( Analog to Digital Converter ) while trim is applied after the ADC as a positive or negative adjustment within the digital domain . Here are some thoughts on how to use each control as the design engineers intended .
Voltage gain is necessary to match the incoming levels across a wide array of inputs to the standard operating level the mixer is designed to process . Typically termed “ line level ” in reference to the 1.23 Volts used in professional gear or the . 316 Volt used in consumer equipment , the basic grasp is : line level is above mic level and below speaker level . Microphones output a weak signal and require amplification to be usable which is provided by the gain circuit pre-amp . Speakers require massive amounts of gain from power amplifiers to produce sufficient acoustic output to be herd in a large space . Other input signals , such as acoustic guitars with pick-ups , bass guitars , keyboards , synth engines and media playback from laptops fall a little above mic level up to true line level for professional keyboards such as a Nord Stage 3 . With such a range of signal sources , the gain control must be employed to bring the input into alignment with the console . One common methodology is to increase the gain with the fader down while the input is played until the meter reads slightly below the 0 point . This process , when used per channel , quickly lines up the inputs and makes the job of mixing easier .
On current digital mixers , an analog source , such as a microphone , is gained via analog circuitry and then converted into a digital signal via the ADC . Once in the digital domain , the trim control can boost or cut the level based solely on ones-and-zeros . The application for trim runs from a simple way to “ fine tune ” a signal to providing a way to adjust the house level without affecting the monitor level when two consoles are used : one for house and one for monitors . If the musicians are wearing ear monitors and the gain is adjusted on the house mixer electric guitar channel , all the musicians will hear the change and it will alter every mix . If , however , the house console trim is adjusted ,
the ear mixes will remain unaffected , assuming the consoles are programmed properly .
When the split between consoles is digital , they share gain but have independent trim . When the split is analog , gain and trim are independent . The advent of livestreaming has brought the need for correct use of trim into focus since adjusting only trim allows the livestream mix to remain consistent regardless of how the house mix is adjusted .
Trim can also be used to balance stereo inputs , such as media players . For instance , if there is a video bumper used between the music and sermon , an out of balance left and right can create sonic issues , so a judicious movement of one trim can bring the stereo spread back into equilibrium .
While gain and trim are similar , gain can be best thought of as the coarse adjustment and trim as the fine adjustment with the added caveat that gain affects everything while trim affects only downstream items .
Kent Morris Kent is a 40-year veteran of the AVL arena driven by passion for excellence tempered by the knowledge digital is a temporary state .