How To Mix Live Music Chapter 6 - Gain Structure — Transcript

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1. 0:07Thanks for joining me in this series of videos
2. 0:10about “How to Mix Live Music”.
3. 0:14This time we have a very important topic,
4. 0:18which I have witnessed even some seasoned professionals
5. 0:22get wrong from time to time.
6. 0:24It is “Gain Structure”.
7. 0:28It is crucial to understand
8. 0:30if you want to get a clean and consistent mix every time!
9. 0:35Consider the complete sound system, from microphone to loud speaker.
10. 0:40There are several points at which the signal can be made louder:
11. 0:44The input gain to the mixing console
12. 0:48The EQ, which we haven’t studied yet
13. 0:51The input channel fader
14. 0:54The Group or DCA fader
15. 0:56The output fader
16. 0:58The speaker processor if used
17. 1:01And the power amplifier
18. 1:04If powered speakers are used,
19. 1:06then you know the power amp will be well matched to the speaker’s ability.
20. 1:11Otherwise, matching amplifier with speaker
21. 1:14is a whole other topic where care needs to be taken.
22. 1:18No time for that right now, sorry.
23. 1:21We are going to look at setting a good gain structure in our simple system,
24. 1:26going directly from mixer output to powered speaker:
25. 1:30Yamaha DSR series in this case.
26. 1:34Looking at the diagram again,
27. 1:36the two gain stages that are able to increase signal level the most
28. 1:41are the input gain of the mixer, the mic pre-amp, and the power amplifier,
29. 1:46which in our case is built into the speaker.
30. 1:49It is crucial to set these well,
31. 1:52to avoid both disturbing hiss during quiet moments
32. 1:56and distortion during loud moments.
33. 2:01Each stage has the ability to add noise to the signal.
34. 2:06And if you start with noise, you will end with more noise.
35. 2:11So its vital to get a clean and clear sound right from the start,
36. 2:16to make things easier to handle
37. 2:18as the signal progresses through the sound system.
38. 2:22In the previous session we talked about setting the input gain.
39. 2:27Now let’s consider amplifier gain.
40. 2:31For simplicity, let’s start with some music playback.
41. 2:35Play some music which is similar in style
42. 2:37and energy to the band that will later perform live.
43. 2:43If you’re using the MGP analog mixer, set the output fader to 0 dB,
44. 2:48and adjust the input level of the iPod or USB
45. 2:52so the output level meter peaks around the 0 dB mark.
46. 3:00With the powered speaker levels at minimum, turn on their power.
47. 3:06Then bring up their level
48. 3:07until you reach the maximum sound pressure level you require in the room.
49. 3:12With the TF mixer, use Stereo Input 1 with the USB connection.
50. 3:18Use the GainFinder to light up the central green indicator.
51. 3:22Set the input channel level to 0 dB, and the Stereo Master fader to 0 dB.
52. 3:28Connect the powered speakers, turn them on and gradually turn them up.
53. 3:34Use some kind of level meter, or even a smartphone app
54. 3:38to check these levels are safe.
55. 3:40Remember that any level above 85 dBA
56. 3:44has the potential to cause hearing damage if endured all day!
57. 3:50Any sustained level above 100 dBA
58. 3:53has potential to cause instant and permanent hearing damage,
59. 3:57and depending on the country or region,
60. 3:59it could even be against the law
61. 4:01if you don’t provide staff with hearing protection!
62. 4:04So please take great care.
63. 4:09For now we should have a comfortable gain structure,
64. 4:12allowing many input channels to be mixed together
65. 4:16without overloading the mixer outputs,
66. 4:19and allowing for some level increase in case of quiet inputs,
67. 4:23by pushing the faders above the 0 dB mark.
68. 4:29Now let’s explain the difference between analog levels and digital levels:
69. 4:35With an analog mixer, 0 dB marks the position of nominal level.
70. 4:41Remember the nominal level is the most suitable signal level
71. 4:44for which the mixer is designed to handle effectively.
72. 4:49The amount of gain above 0 dB is often referred to as “headroom”.
73. 4:55This allows for many channels at nominal level to be mixed together,
74. 5:00and for EQ gains to be adjusted and increased and so on.
75. 5:05But if you push it too far, the signals will gradually distort.
76. 5:10In some cases, this distortion can add a kind of warmth.
77. 5:14Ask any lead guitarist about friendly distortion!
78. 5:19However, in other cases it is not desirable at all.
79. 5:23The level meters turn orange above 0 dB,
80. 5:27then they go red to indicate the onset of distortion.
81. 5:32Avoid the red for a clean and clear sound.
82. 5:37On a digital mixer such as TF series,
83. 5:40there is an absolute maximum level available,
84. 5:44due to the resolution of their analog to digital converters,
85. 5:48the digital signal processing, and the DA, digital to analog, converters.
86. 5:54Great care needs to be taken, to stay below this limit at all times.
87. 6:00Because it can otherwise cause a rather nasty distorted sound
88. 6:04that very few people will be pleased about!
89. 6:08So, to allow enough “headroom”,
90. 6:11we treat the -20 dBFS as 20 dB below “Full Scale”,
91. 6:17as the nominal point.
92. 6:20So -20 dB is equivalent to 0 dB on the MGP.
93. 6:27Notice that on TF, the level meters go orange above -20.
94. 6:33If you’re producing a music track in a studio intended for radio play,
95. 6:38you might see producers trying to get as close as possible to 0 dBFS,
96. 6:45to make the track sound as loud as possible.
97. 6:48Don’t be tempted to do this with a live mix.
98. 6:51Live music is much more dynamic,
99. 6:54often with sudden loud and quiet passages,
100. 6:58which you don’t want to flatten,
101. 7:00as it can create a lifeless experience for the listener.
102. 7:04Keep that headroom available.
103. 7:08There is no advantage to saturate the input of a digital mixer,
104. 7:12because it will not sound warmer like vintage analog consoles can:
105. 7:17they are designed to have a consistent sound character,
106. 7:20no matter what the signal level is.
107. 7:24Digital mixers such as TF have another advantage:
108. 7:29digital gain as well as analog gain.
109. 7:34So, once you’ve set your output and your speaker levels,
110. 7:37if you find the input is still too loud to have the fader at 0 dB,
111. 7:43you will need to either turn the fader or the input gain down.
112. 7:48Now bringing the fader down could bring it into a zone of higher sensitivity,
113. 7:52where small movements cause a large level change.
114. 7:57That will make it tricky to balance with all the other inputs.
115. 8:02Keeping the fader around 0 dB is the safest and most accurate zone for mixing:
116. 8:07especially important with the shorter 60 mm faders of MGP mixers.
117. 8:14On an analog mixer,
118. 8:16turning the gain down would reduce your signal to noise ratio:
119. 8:21there will be a smaller difference
120. 8:22between the loudest and the quietest possible sounds.
121. 8:27But with a digital mixer,
122. 8:28you can keep the analog gain at the optimal position using GainFinder,
123. 8:34and turn down the digital gain
124. 8:37to bring the input’s signal to the required level,
125. 8:41while keeping the fader at 0 dB.
126. 8:45Because digital mixers these days have a much greater dynamic range
127. 8:50than they did over 20 years ago,
128. 8:53you won’t be making any quality compromise.
129. 8:59One more piece of advice on this topic:
130. 9:02I have seen some engineers who want to keep their amps turned up
131. 9:06to maximum all the time, no matter what.
132. 9:10Perhaps for convenience, laziness, habit, whatever.
133. 9:14But if you do this, you may be forced
134. 9:17to reduce the gain at some other point in the signal chain.
135. 9:22Perhaps at the stereo output of the mixer,
136. 9:25or even at the mic pre-amp.
137. 9:28This is not optimal:
138. 9:30adding un-necessary gain at the amplifier
139. 9:34will raise the “noise-floor” of your system,
140. 9:36meaning background hiss will be more noticeable at quiet times.
141. 9:41It will compromise the sound quality during quieter moments.
142. 9:47Running the amps at a reduced level can not only provide a better sound:
143. 9:52it will also help them to stay cooler, be more efficient, and last longer.
144. 10:00In the next few videos,
145. 10:01I’m going to explain about high pass filters and parametric EQ.
146. 10:07Essential tools for shaping the sounds picked up by the microphones,
147. 10:12and also for shaping the sound of the speakers to suit the venue.
148. 10:17Don’t miss it!