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Connections, levels & preamps. Review
Transcript of Connections, levels & preamps. Review
One wire carries the signal
While the shield protects
it from electromagnetic
and radio interferences
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)
RFI (radio frequency interference)
if noise makes its way to the wires, it will be in the same phase on both.
On the other end, the phase of one of the signals is flipped again
Now the two
, and are added up!
out of phase
, therefore gets canceled!
The result is a boost in amplitude and a cleaner signal.
Mini TRS (1/8")
In order to be balanced, an audio connection needs at least
(shield, cold, hot), two of them carrying the
They could carry two
applications, but would then become
Good for carrying strong signals for a short length.
Don't support long cable runs
Susceptible to noise interference
Good for carrying both soft signals, such as signals from microphones
Support longer cable runs
Less prone to noise interference.
), power cables and audio cables should be far from each other.
If they have to be close, minimize the contact area.
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?
Use to interconnect studio
equipment through a
at which a device is
Converters, speakers, microphone preamplifier, mixing consoles...
They are all designed to operate at a certain
nominal level or voltage.
The nominal level for
What does that mean?
The amplitude of this signal is "perfect" for a
professional LINE LEVEL
Most audio devices can handle signals
the nominal level up to a
clipping/distortion point, usually around +24dBu.
1.228V RMS (+4dBu)
Headroom: the difference in
Signals above this level will clip/distort.
20dB of headroom!
Useful to accommodate fast, loud transients, that briefly
the nominal level
Analog devices start distorting
when they enter the
up to point of
3.9V RMS (+14dBu)
12.3V RMS (+24dBu)
Each device distorts in a different way.
1.228V RMS (+4dBu)
12.3V RMS (+24dBu)
- The output level of a microphone is usually very low, in between -50 to -20dBu
Before going to a tape machine or an analog to digital converter to be
, 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.
The signal of electric guitars, basses, keyboards, etc...
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
But there's a step in between:
A DI(Direct Injection) box is a device that convert an
unbalanced, Hi-Z signal
That can then be sent to a mic pre-amplifier
Unbalanced, medium level
Balanced, low 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
The nominal level for professional LINE LEVEL devices is +4dBu or 1.228V RMS
, often found on audio equipment, indicates if a device is operating at its nominal level.
0VU = +4dBu = 1.228V
= nominal, good level for
Could be based on
circuits, each one with a different
Focusrite ISA RED. Solid-state
Universal Audio 2-610. Tube
determines the amount of amplification being applied to the input signal.
Inverts the phase of the signal.
48V used to drive condenser microphones.
attenuates input signals that are
(high) for the proper operation of the preamp.
could also be indicated
by the symbol
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.
Batteries, microphone pre-amplifiers, consoles or mixers.
Look for the logo and the polar pattern symbol.
bi-directional or figure 8
An increase in bass response when a mic is placed close to the sound source.
Balanced and unbalanced
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
Peak and RMS.
The maximum amplitude of a waveform.
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)
Average = 0+7.8+16+7.8+0+7.8+16+7.8
measurement 7: -4V
measurement 8: -2.8V
RMS = +2.8V
Peak = +/-4V