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Connections, levels & preamps. Review

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Exati Tecnologia

on 11 September 2017

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Transcript of Connections, levels & preamps. Review

Connections, Levels & Preamps
Thank you!
Audio Connections
Two categories:
Balanced
Unbalanced
Unbalanced:
One wire carries the signal
While the shield protects
it from electromagnetic
and radio interferences
The cable
Connectors
Balanced
The output of the microphone is duplicated, but the replica has its phase inverted.
Both signals travel through two different wires.
A shield protects both signals from
EMI (electromagnetic interference)
and
RFI (radio frequency interference)
+
-
shield
(ground)
if noise makes its way to the wires, it will be in the same phase on both.
noise!
On the other end, the phase of one of the signals is flipped again
Now the two
signals
are
in phase
, and are added up!
But the
noise
becomes
out of phase
, therefore gets canceled!
The result is a boost in amplitude and a cleaner signal.
going up.
going up
going down
Balanced connections:
The cable:
Connectors:
XLR
TRS (1/4")
shield (ground)
hot
cold
Mini TRS (1/8")
In order to be balanced, an audio connection needs at least
3 wires
(shield, cold, hot), two of them carrying the
same
signal.
They could carry two
different
signals for
stereo
applications, but would then become
unbalanced
.
Example:
Balanced
Unbalanced
Good for carrying strong signals for a short length.
Cheaper
Don't support long cable runs
Susceptible to noise interference
Good for carrying both soft signals, such as signals from microphones
and
strong signals.
Support longer cable runs
Less prone to noise interference.
More expensive
Tip
To avoid
EMI
(
electromagnetic interference
), power cables and audio cables should be far from each other.
If they have to be close, minimize the contact area.
Bad:
Audio
Power (AC)
Better:
Audio
Power (AC)
Break???
Remember everything?
What are the three most common types of microphones?
In order to operate, condenser microphones need a power supply, also called?
How can one tell where the front of the mic is?
Figure 8 microphones don't exhibit proximity effect. True or False?
Name the following polar patters:
What is proximity effect?
What is the most common polar pattern for ribbon microphones?
Audio connections can be divided into two categories. They are?
How many wires are needed to carry a balanced audio signal?
Advantages of balanced connections over unbalanced connections?
Balanced/Unbalanced, name and applications?
+
TT (Patchcords)
Use to interconnect studio
equipment through a
patchbay

Levels (Electrical)
+1.8V
-1.8V
Peak!
RMS
+1.3V
Mic Level
Instrument Level
Line Level
Nominal Level
Nominal Level
The
operating level
at which a device is
designed
to operate.
Converters, speakers, microphone preamplifier, mixing consoles...
They are all designed to operate at a certain
nominal level or voltage.
The nominal level for
LINE level
devices is:
+4dBu (1.228V),
BALANCED
for
professional audio
gear.
What does that mean?
compressors
equalizers
converters.
The amplitude of this signal is "perfect" for a
professional LINE LEVEL
device.
0V
AMPLITUDE
TIME
Most audio devices can handle signals
above
the nominal level up to a
clipping/distortion point, usually around +24dBu.
OV
1.228V RMS (+4dBu)
Headroom: the difference in
dB
between the
nominal level
and the
distortion
point.
Distortion!
Signals above this level will clip/distort.
20dB of headroom!
Useful to accommodate fast, loud transients, that briefly
overshoot
the nominal level
Analog devices start distorting
gradually
when they enter the
distortion zone,
up to point of
complete failure.

3.9V RMS (+14dBu)
Distortion zone.
12.3V RMS (+24dBu)
Each device distorts in a different way.
1.228V RMS (+4dBu)
12.3V RMS (+24dBu)
MIC LEVEL
- The output level of a microphone is usually very low, in between -50 to -20dBu
MIC LEVEL
(0.025V
RMS
or -30dBu)
very low!
Before going to a tape machine or an analog to digital converter to be
recorded
, the signal has to be boosted up to
LINE LEVEL, which is a lot higher.
That's the role of the
microphone preamplifier, or mic preamp.
INSTRUMENT LEVEL
The signal of electric guitars, basses, keyboards, etc...
INSTRUMENT LEVELS
are
unbalanced, medium
voltage,
high impedance (Hi-Z)
and are expected to be amplified by a cabinet.
However, we can record them without using a cabinet.
But before recorded,

they need to be brought up to
LINE level
But there's a step in between:
The DI:
A DI(Direct Injection) box is a device that convert an
unbalanced, Hi-Z signal
.
Into
MIC LEVEL
signal
(balanced, low-impedance)
That can then be sent to a mic pre-amplifier
In SUM...
Unbalanced, medium level
Balanced, low level
DI BOX
MIC PREAMP
INSTRUMENT LEVEL
MIC LEVEL
LINE LEVEL
balanced, stronger, ready
to be recorded
Some mic preamps have
dedicated Hi-Z inputs
, therefore not requiring a DI
Just look for an
"INST", "DI" or

"HI-Z"
input.
LINE LEVEL
The nominal level for professional LINE LEVEL devices is +4dBu or 1.228V RMS
A
VU meter
, often found on audio equipment, indicates if a device is operating at its nominal level.
0VU = +4dBu = 1.228V
= nominal, good level for
LINE LEVEL
devices.
Could be based on
solid-state
,
vacuum tube
, or
hybrid
circuits, each one with a different
sonic
character.
Mic Preamplifiers
Focusrite ISA RED. Solid-state
Universal Audio 2-610. Tube
Common features:
Gain:
determines the amount of amplification being applied to the input signal.
Phase/Polarity:
Inverts the phase of the signal.
or
Phantom Power:
48V used to drive condenser microphones.
PAD:
attenuates input signals that are
too hot
(high) for the proper operation of the preamp.
API 512c
could also be indicated
by the symbol
Neve 511
HPF:
High Pass Filter. Cuts the low end (low frequencies) of the signal
Preamps: final thoughts
- Because they amplify the signal of the microphone so many times, they are a very important part of the signal chain.
- Can cost from $10.00 to more than $2 000.00 per channel
- How different do they sound from each other?
Universal Audio 4-710. Hybrid
Omnidirectional microphones don't exhibit proximity effect. True or False?
Phantom power can be provided by?
Dynamic and ribbon microphones need phantom power to operate. True or false?
What is the role of a microphone preamplifier?
What are three common types of signal in analog audio devices?
List common features of a mic preamp:
A DI converts instrument, Hi-Z signal into?
Professional, balanced LINE LEVEL audio inputs and outputs have a nominal level of?
What is headroom?
What does this symbol mean?
Dynamic, ribbon and condenser microphones.
Phantom Power
Batteries, microphone pre-amplifiers, consoles or mixers.
ABSOLUTELY FALSE!
Look for the logo and the polar pattern symbol.
cardioid
omni
bi-directional or figure 8
super cardioid
figure 8
An increase in bass response when a mic is placed close to the sound source.
FALSE
TRUE
Balanced and unbalanced
3
Less susceptible to noise, allow for longer cable runs
Mic level, Instrument level, Line level
+4dBu or 1.228V
The difference in decibels between the nominal level and the distortion point of a device.
Boost a mic level signal up to line level.
Mic level signal.
48V (phantom power), Polarity/Phase, PAD, HPF
Phase/Polarity reverse
Levels:
Peak and RMS.
Peak:
The maximum amplitude of a waveform.
5V
-5V
Peaks: +4V and -4V
What if we want to measure the average over time?
measurement 1: 0V
measurement 2: +2.8V
measurement 3: +4V
measurement 4: +2.8V
measurement 5: 0V
measurement 6: -2.8V
Average = 0+2.8+4+2.8+0+(-2.8)+(-4)+(-2.8)
8
= 0
negative!
( )
2
Average = 0+7.8+16+7.8+0+7.8+16+7.8
measurement 7: -4V
measurement 8: -2.8V
( )
2
( )
2
( )
2
( )
2
( )
2
( )
2
( )
2
=0
=+7.8
=+16
=+7.8
=+7.8
=+7.8
=0
=+16
8
=
63.2
8
= 7.9
= +2.8V
RMS = +2.8V
Peak = +/-4V
Full transcript