Presentation on theme: "Gain structure, Getting it right"— Presentation transcript:
1 Gain structure, Getting it right Gordon Moore CTS
2 GainThe change in level imposed on an electrical signalGenerally measured in decibels3 dB is a doubling of powerYou need 6 dB to make up for moving twice the distance from a source – a quadrupling of power
3 Gain10 dB changes the level by a magnitude of ten (10X or 1/10th )20dB changes the level by hundred (100X or 1/100th)60 db raises the level a thousand (1,000 or 1/1,000th)
4 Why is Gain needed?Microphones generate VERY low voltage levels – measured in millivolts.This very low signal needs to be amplified to around a volt to be strong enough for long cable runs.
5 Why is Gain needed?Very low levels are susceptible to interference from electro-magnetic and radio frequency sources. Amplification makes these signals much more resistant to these sources.Processing works much better and quieter at higher voltage levels.
6 Where is the biggest amplifier? The microphone preamp has the greatest effect on your relative signal levels and S/N ratios. It is, in general, the most amplification you will apply in most systems.Get the preamplifier right and everything else falls into line
7 Gain is KINGProper gain staging makes or breaks performance at all levels.It can:Affect signal to noise ratio in the entire systemAffect the proper operation of signal processorsDSPConferencing systemsAudio processorsAffect wireless microphone performance
8 What is gain stagingThe optimization of the signal level so all components in the signal chain are operating within their optimal performance range without detriment to signal integrity.OrSetting the levels right…………………..
9 Signal to noise ratio Poor S/N Ratio Line Level Mic Level Noise Floor PreampMixerSignal processorsAmps
10 Signal to noise ratio Line Level Good S/N Ratio Mic Level Noise Floor PreampMixerSignal processorsAmps
11 Signal to noise ratio Line Level Mic Level Noise Floor Mic Preamp MixerSignal processorsAmps
12 Two methods to be discussed Unity gain stagingSystem optimization
13 Common attributesBoth, when properly engaged, will provide improved signal to noise ratio.Both require some minor specialized equipmentSignal generatorTone and/or pink noiseSignal analyzerSimple as Multimeter or even cheap piezo tweeterMisc cables with all sorts of connector combinations – great soldering practice
14 Oscilloscopes, Audio analyzers or other stuff requiring $$$$$$$$$$$$ Good news– Neither method requires really expensive equipment. You DO NOT needOscilloscopes, Audio analyzers or other stuff requiring $$$$$$$$$$$$
15 IT DEPENDS Why two methods? The correct answer in all questions audio isIT DEPENDS
16 Unity Gain MethodInvolves setting all line level outputs to one common levelMost often 0dBu (.775Volts) or +4dBu (1.94V)Use – permanent installed sound systems such as courtrooms, conference centers, boardrooms, paging etc – primarily voice reinforcement systems
17 Unity Gain Method Advantage – maintenance is simple – pull out device A,replace with device B,set output level to 0dBu,voice test,Go home, drink cold beverageUnity gain – 0dBu in to 0dBu out.
18 Unity Gain MethodWhy 0dBu or +4dBu?Most systems need “headroom” – generally 20dB will handle anythingMost professional gear can handle up to +20dBu (77.5V) signals (professional theatre or touring gear up to +28dBu)Capping “normal” level at 0 allows up to 20dB of extra loud signal before distortion or clipping
19 ClippingDriving an amplifier circuit to the point where signal levels cannot go any higher.OVERDRIVEN signals create distortion and harmonicsCan overheat components and destroy speakers.Guitar amplifiers/speakers that must handle distorted guitars require much heftier components than most home systems can handle.Example
20 Unity Gain Method Requires signal generator – tone and pink noise Meter to measure output
22 Another option http://www.world-voices.com/software/nchtone.html Or Google “Tone generator free”
23 Insert Known signal into input at TOP of chain Unity Gain MethodInsert Known signal into input at TOP of chainTop = first audio insertion point – microphone input on mixerKnown signal can be any level – but you must know what that level is.Set input trim to set 0dBu level(if input signal is -20dBu, set input trim at +20 to get 0)
24 Unity Gain MethodSet output level to measure 0dBu (or .775V with multimeter set on AC)Go to next device – set input and output gain so level at output is also 0dBuSet amplifiers last – if all else is set right and amps are properly chosen, typical amp level will be “low”.
25 Until you get to amplifiers, there is NO need to have amplifiers ON. Unity Gain MethodUntil you get to amplifiers, there is NO need to have amplifiers ON.When setting amplifier, use typical test signal and set levels in room using SPL meter(or even by ear, not documentable however)Equalize then reset equalizer output to 0dBu.
26 Unity Gain Method Basic system gain is correctly set. Any changes to any signal processors, (compressors, limiters, etc) will require a reset of that piece of gear back to unity gain.
28 System optimizationSetting every component so that clipping occurs at exactly the same time in all devices. If “clip” indicator shows nothing on main console, you know everything else in your system is not going to “clip” either. All components can be driven to their maximum without danger.
29 System OptimizationWHEN to use? Live sound systems and theatrical installations where the sound operators may need to drive the system to “Max”. This optimizes the signal to noise ratio and permits full signal range. Requires complete re-calibration if any components are replaced.
30 System optimizationTwo ways to do this – one requires expensive gear, the other doesn’t Lets go cheap first You need
31 CHEAP STUFF1 – very cheap piezo tweeter – generally available for less than $10.2 – one signal generator that can generate an A on the scale 440Hz (or something near that level)If you have a laptop, you can get free on-lineIf not, music stores have generators for less than $50.
36 System optimizationStep one – connect speaker to output of first device (generally the mixer)Step two – set output level at 0, faders at 0, subs at 0.Step three – insert tone into input of mixer. Increase gain at input until speaker makes squealing sound (you are clipping) – back input gain down until silent.
37 System optimizationAt this point, leave all controls at mixer alone – do not changeRepeat test at each input and output of all line level devices downstream.When you are finished, all devices will clip at the same time.
39 System optimizationExpensive method – replace free laptop software with fancy signal generator and speaker with O-Scope.Results will be exactly the same.If you lose the speaker or it gets stolen – oh well.If you lose the O-scope ………….
41 Setting mics Based on application and varies according to mic. Set input trim to give 0dBu nominal levelCan shouting distort the audio (clipping!)?If Yes, turn it down a bit until answer is no.
42 Setting Multi-Media Use known reference – as in KNOWN to YOU Ideally a measured sample – so you can document the setup and resultDoes not have to be boring test signals
43 Setting Multi-Media I use Diana Krall, “Live in Paris” Reasons – Wide dynamic range (soft to loud)Wide frequency range (bass to cymbals)Available in DVD and CD formatI also use boring test CD as well. ZZZZZZZZZZZZZZZZZZPink noise drives out unwanted visitors.
44 Setting wireless mics Transmitter gain affects FM modulation The modulation of the signal affect S/N ratioPoor modulation makes apparent range lowerGetting transmitter gain “hot” improves FM performance
45 Setting Wireless Microphones Again – avoid distortion but don’t set too lowDepends on situation – does scene require screaming? Or simply talking?Then set output of receiver according to input in the mixer you are using.Line level preferred – better resistance in RF and EMI
46 So, why is this important again? If gain is consistently set at optimal levels you get three benefits
47 Benefit 1 – Far side v near side in conferencing – relative levels between sources will be evenFar side v near side in conferencingDial tones v incoming phone levelMulti-media v voices
48 Benefit 2 Processing functions will work at their best Compressors, limiters, automixers, equalizers, etc
49 Benefit 3– Signal to noise ratio will be at best possible result
50 SummaryMaximum modulation with good headroom will give best signal to noise ratio.Set ALL stages (don’t forget any inputs)