FUMC Sound Tech Course 20062 Session 4

1
FUMC Sound Tech Course2006-2Session 4

• EQUIPMENT
• Mixers Signal Processors
• (EQ, Compressor/Limiters, FX, Delay, Feedback
  Suppressors)

2
Mixers

• Mixer Function
• Combine and route multiple input signals to one
  or more sets of outputs (possibly many outputs!)
• Terms
• Mixer Generally lt 10 or 12 input channels
• Console Generally gt 12 input channels
• British name for Console is a Desk
• Mixer Console terms used interchangeably
• Line Mixer Rack mount w/8-16 channels

3
Mixer Block Diagram
Mixer Components Preamps Equalizers Line Amps Bus
Structure Output/Master Section
4
Preamps

• High Gain/Low Noise SINGLE (mono) input Amplifier
• Boosts weak ( -70 to -50 dBu) mic signals to -20
  to 4 dBu (.1V to 2 V range
• Probably the highest design requirement for any
  mixer component
• Should not be operated at Unity Gain
• Become unstable at unity gain
• Use Attenuator Pad to reduce input level and run
  some gain

5
Mixer Signal Levels
All other parts of Mixer (EQ, FX, Inserts,
Faders, Summing Amps, Output Sections) Run at
approx 0dBu (1V) levels
Preamp
Line Inputs -20dB (100 millivolts)
Mic Inputs -60dB (a few millivolts)
6
Preamp Section

• Yamaha GA32/12 Mixer (FUMC Sanctuary)
• 1. Pad Switch 26dB attenuation
• 2. Gain (Trim) Pot
• 3. Phase Reversal Switch
• 4. Low Frequency Cutoff Switch (80Hz)
• 5. Peak Indicator (3dB below Clipping)
• 6. Equalization Section
• High low Shelving Sections
• Lo-Mid Hi-Mid Semi-parametric
• 7. EQ On/Off Switch

7
Mixer Block Diagram
Mixer Components Preamps Equalizers Line Amps Bus
Structure Output/Master Section
8
Stereo Channel Preamps

• 2 Channels ganged together
• Lower Preamp Gain
• Few stereo channels
• Line Inputs (Unbalanced - 1/4 inch (not XLRs))

9
Master/Output Control Section
8. M1-M4 mix level controls 9. M1-M4 mix ON/OFF
switches 10. M5-M10 mix level controls 11.
Pre-Post Fader switches 12. Pan Pot 13. Stereo
Bus switch 14. Channel ON switch 15. PFL
(Pre-Fader Listen) switch 16. Channel Fader
10
Panpot Function
Panpot position determines how much channel
signal goes to L R stereo channels We operate
FUMC systems in Mono mode so Panpots are not
effective
11
Mixer Buses Outputs
12
Mixer Input/Output Back Panel Connectors
13
Mixer Block Diagram
Mixer Components Preamps Equalizers Line Amps Bus
Structure Output/Master Section
14
Mixer Output Sections
Mix Section
Stereo Section
15
Other Mixer Functions

• Talkback (Mixer Mic output to Mains/Monitors)
• Headphone Monitor (PFL/AFL)
• AUX Sends Returns
• Matrix mixes
• INSERTs
• Phantom Power
• Signal Level Metering

16
Overloading Summing Amps

• Channel outputs add in Root-Mean-Square (RMS)
  fashion in Output Section amps
• 1 Chan _at_ 1V RMS ea. 1V RMS in Output Section
• 2 Chan _at_ 1V RMS ea. 1.414V RMS in Output
  Section
• 4 Chan _at_ 1V RMS ea. 2V RMS in Output Section
• 16 Chan _at_ 1V RMS ea. 4V RMS in Output Section
• The more channels you have active, the more you
  have to watch clipping in the Master/Output
  Section.

17
Direct Box

• Used to connect higher level, unbalanced inputs
  (such as guitars, electric pianos) to a Mic input
  (balanced XLR cable)

Direct Box
Input
XLR Cable to Mixer
Output
Instrument Cable
Gnd Lift Switch
18
Equalizers (EQs)

• Common Tone Controls
• Shelving Low High w/
• Sweepable center freqs

19
Equalizers

• Graphic EQs
• Name comes from face of EQ
• 2/3 octave (15 band) or 1/3 octave (31 band) most
  common
• ISO standard center freqs
• 20, 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200,
  250, 315, 400, 500, 630, 800, 1K, 1.25K, 1.6K,
  2.0K, 3.15K, 4K, 5K, 6.3K, 8K, 10K, 12.5K, 16K,
  20K Hz
• Controls
• Bypass, Low Pass, High Pass, Gain, Range (6 or 12
  dB), Clip indicator

20
Equalizers

• Parametric EQs
• Independent Cut/Boost, Center Freq Bandwidth
  (Q) adjustments
• Q is measure of filter steepness (Q.5 is broad
  filter, Q3-5 is narrow filter)
• Allows mixing matching filters for feedback
  elimination or general contouring
• Complex to set up

21
Using Equalizers

• Measurement Method
• Use Pink Noise input
• Use Real Time Analyzer to
• see system/room response
• Adjust EQ to flatten response
• (Ultra-flat response not necessarily best
  sounding)

22
Using Equalizers

• Ringing Out Method
• Open normally used mics
• Increase Gains until 1st feedback freq occurs
• Adjust EQ to reduce feedback
• Increase Gain to find reduce other FB freqs
• Adjust EQ for best sound

Remember Peaks in response reduce gain
margin (before feedback) and headroom (before
clipping)
23
Feedback Eliminators

• Digital Signal Processor
• Uses very narrow ( to 1/60 Octave) filters
• Automatically finds multiple FB frequencies
  moves filters to suppress them
• 9 to 12 filters per channel
• Some remain fixed and some float to handle
  moving mics, temperature changes, etc

24
Compressor/Limiters

• What if you had a 90 dB dynamic range signal and
  your system would only handle a 74 dB dynamic
  range? What to do?
• Use a Compressor

25
Compressor/Limiters
Amplifier Response - Linear
Clip Region
Slope of graph Amp Gain
V out
V in
26
Compression

• Compressor Adjustments
• Compression Ratio
• Threshold

NOTE FUMC uses compression on Pastors mics and
vocal mics
27
Compressor Design

• Attack Time
• Time it takes VCA to change gain
• Release Time
• Time it takes VCA to return to original gain
• Both Attack Release are adjustable
• Can lead to pumping

Side Chain
28
Noise Gate(Upside down Compressor)

• Noise Gating mutes sounds that are below the Gate
  Threshold to
• Reduce background noise
• Increase percussive sound in drums
• Cut out noise in soft passages
• Threshold Ratio are adjustable

V in
29
Effects Units (FX)

• Digital Processors that provide
• Reverb
• Delay
• Chorus
• Flange
• Pitch Shift
• Gate/Expander
• De-Esser
• Compressor/Limiter
• FUMC uses M-One FX units by tc electronic

30
Delay Units

• Delays audio signal in time
• Mechanical (Spring transducers Old)
• Digital (signal is A/Dd digitized, put into a
  circulating register for delay time, then D/Ad
  back to analog
• Use
• Speaker delay (Shark DSP 110)
• Effects Units

31
Power Sequencer

• Remotely controls AC power to system
• Provides separate, delayed power outputs
  (normally 4 to 6 outputs)
• Prevents thumping speakers power spikes by
  high power amps

1
Rack mounted Delay Unit (5 sec)
AC Outlet
On/Off Switch/ Keypad
110 VAC
Remote Relay Unit
6

• ON sequence
• Mixer, Decks, Processors (Sound Booth)
• 2. Amp rack electronics
• 3. Amp 1
• 4. Amp 2
• 5. Amp 3
• OFF sequence 5 4 3 2 - 1

32
Bibliography

• Sound Reinforcement Handbook by Gary Davis
  Ralph Jones
• Guide to Sound Systems for Worship by Jon Eiche

33
Thats All Folks!!
34
Audio Equipment Measurementsof Interest

• Power Watts Amps x Volts
• Resistance Ohms, Kilohms, Megohms
• Impedance Complex Resistance
• Similar to Resistance
• Ohms
• Voltage Volts, Millivolts, Microvolts
• Current Amps, Milliamps (1/1000 amp)

35
Ohms Law

• I V / R (Current Voltage / Resistance)
• Other forms are also valid
• R V / I
• V I x R
• E is often used instead of V (for voltage)
• IE/R
• Power I x V V² / R I² x R

36
Amp Power Output

• We have a 1000 Watt Amplifier feeding a 10 Ohm
  speaker impedance.
• How much current can it supply?
• If an Amp can supply 50 volts RMS into a 4 Ohm
  speaker load, what is its Output Power?

37
Mixer (GA32/12) Block Diagram
Signal Flow (Audio Level) Diagram