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Morset Sound Development
Sound System Calibration
Example - Performing
Monitor Calibration
in Studios
Morset Sound Development
IntroductionIntroduction
• Setting up the measuring equipment• Ambient sound levels• The effect of reflections• Impulse and Frequency Responses• Acoustical problems in rooms• Reflection diagnosis & causes of reflections• Tone controls on different monitors• Calibration standard• Practical calibration of monitors• Subjective evaluation
Morset Sound Development
Connecting the Measuring SystemConnecting the Measuring System
Laptop Computer
XLR LeftLine Output
Digigram VXpocketPCMCIA Sound Card
XLR RightOptional loop-back(for synchronisation)
XLR LeftMic. Input
AKG PhantomPower Supply
GENELECR
Neutrik 3382Microphone
Active Monitor
- example using VXpocket sound card and Neutrik mic.
Morset Sound Development
Positioning the MicrophonePositioning the Microphone
• At the listening position
• At average ear height (1.4m)
• Vertically NOT horizontally
• On a good microphone stand
Morset Sound Development
Why is the microphone angled at 90Why is the microphone angled at 90ºº
Morset Sound Development
Ambient Sound LevelAmbient Sound Level(Signal-to-Noise Ratio)(Signal-to-Noise Ratio)
Amb ient Sound in Listening R oomTest Level vs Ambie nt Level
-4 0
-3 0
-2 0
-1 0
0
1 0
2 0
3 0
4 0
1 0 10 0 1, 00 0 1 0 ,00 0 1 0 0,0 0 0Fre qu e n cy, H z
Le vel, dB
E xa m p le S pe a ker Te st L e ve l
Am bie n t L eve l S a m pl e
Morset Sound Development
The Effects of ReflectionsThe Effects of Reflections
0Time
0Freq
0Time
0Freq
td 1/td
Time domain Frequency domain
Morset Sound Development
Subjective Perception of ReflectionsSubjective Perception of Reflections
Time, ms
Level, dB
0
-10
-20
-300 20 40 60 80
IMAGE SHIFT
ECHOS
USEFUL EARLY ENERGY
RE
VE
RB
ER
AT
ION
TO
NE
CO
LOU
RA
TIO
N
NO REFLECTIONS HEARD
0 6.8 13.6 20.4 27.2 Distance, m
Morset Sound Development
Room Impulse ResponseRoom Impulse Response
t = 0Time
Input DirectSound
1st Reflection
Discrete Early Reflections
Noise Floor
Reverberant(Diffuse) Field
Time of Flight Initial Time
Gap, td
50-80 ms80+ ms
Morset Sound Development
Typical Studio Impulse ResponseTypical Studio Impulse Response
Time Data - 1039AL reflections example
Name: ...\Measurements\1039AL reflections example.wmb Comment: Measured - 17:23:58, 13Aug2001 Plotted - 17:54:14, 25Sep 2001
Distance [meter]12011511010510095908580757065605550454035302520151050
Pres
. [Pa
] / [v
olts
], Li
near
0.055
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
-0.005
-0.01
-0.015
-0.02
Morset Sound Development
First 15First 15mm (44ms) (44ms) of of the the Impulse ResponseImpulse Response
Time Data - 1039AL reflections example
Name: ...\Measurements\1039AL reflections example.wmb Comment: Measured - 17:23:58, 13Aug2001 Plotted - 17:54:14, 25Sep 2001
Distance [meter]1514131211109876543210
Pres
. [Pa
] / [v
olts
], Li
near
0.055
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
-0.005
-0.01
-0.015
-0.02
Time of Flight
Impulse from Monitor (direct sound)
Reflection off Mixing Desk
Reflection off CeilingReflection off Rear Wall
Reflection off Side Wall
Morset Sound Development
Reflections in the Frequency DomainReflections in the Frequency Domain
Magnitude Frequency Response - 1039AL reflections example
Frequency [Hz]10 100 1,000 10,000
Pres
. [Pa
] / [v
olts
], dB
5
0
-5
-10
-15
-20
-25
-30 Reflection off Rear Wall
Reflection off Side WallMonitor angled off axis to listening position
Reflection off Ceiling Reflection off Mixing Desk
Morset Sound Development
Typical Acoustical ProblemsTypical Acoustical Problems
Front Wall and Floor• Front wall should have no discontinuities (the front glass
window, doors, etc. should all be flush)• When less than 1.2m from the floor, floors reflections can
dominate• Bass trapping can be implimented in the front wall but
beware of the ¼ wavelength cancellation with the hard wall behind the monitors
• Main monitors are usually mounted with a vertical angle of about 15º - 20º
Morset Sound Development
Typical Acoustical ProblemsTypical Acoustical Problems
Console, Equipment and Furniture• First order reflection off the mixing console surface creates
a dip around 1 – 3kHz. Vertical positioning of 2-way is necessary in all cases
• The ¼ wavelength cancellation with the hard wall behind the monitors is often a problem with near-field monitors
• Meter bridge, large tables, computer monitors and racks all create ripples and comb filtering in the mid band
• Computer monitors should be tilted and mounted into the furniture. Flat screens are acoustically better
• Open furniture is acoustically more transparent
Morset Sound Development
Typical Acoustical ProblemsTypical Acoustical Problems
The Ceiling and the Side Walls
• Hard reflective ceilings close to the monitors create strong reflections. Bumps and dips can be seen around 3 – 5kHz
• Ceiling construction close to the monitors should not induce first order reflections
• Various design philosophies exist for side wall construction but symmetrical treatment is essential
Morset Sound Development
Typical Acoustical ProblemsTypical Acoustical Problems
Control Room Layout Recommendation
• No control room design should have parallel walls• No control room should be installed in a ’shoe box’ type
rectangular room. Standing waves will be hard to control• All equipment in the room should be placed in a symmetrical
layout arrangement• Enough (thick) damping material should be built in the
trapping to handle very low frequency absorption
Morset Sound Development
Typical Causes of Cancellations in StudiosTypical Causes of Cancellations in Studios
• 3kHz – 5kHz Compression ceiling• 1kHz – 3kHz Mixing console• 250 Hz – 1kHz Furniture, etc• 70 Hz – 250Hz Floor• Under 200Hz Rear wall of studio?
Side walls of studio?
Wall behind monitor?
Morset Sound Development
Diagnosis of the Causes of ReflectionsDiagnosis of the Causes of Reflections
• Move the microphone about 30-40 cm in one direction at a time– Left / Right … side wall reflections– Up / Down … floor / ceiling reflections– Forwards / Backwards … rear wall reflection
• No change indicates monitor rear wall reflection• Dip moves down indicates longer path length• Dip moves up indicates shorter path length
Morset Sound Development
Calibration StandardCalibration Standard
• High quality monitor design tolerance is +/-2.5dB over the whole pass band when measured in anechoic conditions
• This can also be achieved in a good studio with well controlled acoustics
• The calibration target is to fit the whole bandwidth of the frequency response within a 5dB window
• WinMLS lets you overlay a 5dB guideline
Morset Sound Development
Calibration StandardCalibration Standard
• WinMLS system gives you about 80% of the information about the calibration
• The listening process (about 20%) lets you check for colouration, harshness, unfocused imaging, tonal changes etc
• The monitor balance has to be right at the mix position where the engineer does most of his/her work
Morset Sound Development
Broken TweetersBroken Tweeters
Effects of Broken Treble Drivers
60
65
70
75
80
85
90
95
100
105
10 100 1,000 10,000 100,000
Gain, dB1033A
1035B
Morset Sound Development
Subjective Evaluation of CalibrationSubjective Evaluation of Calibration
• Use a large variety of source materials:– Orchestral, Big Band, Female vocal, rock, etc.
• Listen for the following:– Smooth bass with no obvious bumps or holes – Bass content should not mask vocals & guitars– No upper midrange hardness at high SPL– Midrange & HF in balance
Morset Sound Development
Calibrations Session SummaryCalibrations Session Summary
• Remove the obvious causes of reflections to get a better response with less ripple– Move the monitors around in the room– Move equipment around in the room– Recommend appropriate acoustic treatment (maybe?)
• Move the microphone to find the source of reflections• Tone controls are for acoustical loading correction and do
not solve the problems of poor acoustical design• Reflections CANNOT be equalised out using tone controls• The calibration standard is +/- 2.5dB
Morset Sound Development
ConclusionsConclusions
• Setting up the measuring equipment• Ambient sound levels• The effect of reflections• Impulse and Frequency Responses• Acoustical problems in rooms• Reflection diagnosis & causes of reflections• Tone controls on different monitors• Calibration standard• Practical calibration of monitors• Subjective evaluation