Wk4 Flashcards
How does a speaker work?
In a speaker when an electrical signal is sent through the copper wire it, the magnetic field induced around it causes it to move in the magnet. This in turn vibrates the diaphragm making sound emanate from the speaker
Signal Flow/how does that relate to a mixing console
Signal Flow - Tracing signal from source to destination
Mixing desk manages the signal flows from all that are plugged in
Channel Strip (MC)
Each channel strip is an exact or close
duplicate, and each one allows for a separate signal to come into the desk.
Sound can be amplified, attenuated, processed, sent elsewhere, or grouped using channel
strips.
Mic Preamp (MC)
The mic preamp section of the desk is
where signal first comes into the desk,
and where we can adjust the input gain.
In this section you will often find:
* phantom power,
* phase reversal and
* hi-pass filter switches.
Phantom Power
Power source for a condenser microphone provided by audio
interface, preamp, or mixing console
Difference between Microphone Signal and Line Level?
Microphone signal is significantly lower than the line level and require
amplification.
Line level signals are around 1000 times higher than mic signals.
* Microphone inputs feed microphone pre-amplifiers, which are amplifiers that bring the microphone level signal up to line level signal.
* Mic preamps usually have between 60 & 80 dBu of gain available.
What are the two Line Level types
Consumer and Professional.
* Consumer line level is generally thought of as a signal whose level is at -10 dBV
(0.316). Ex: CD players and DVD players.
* Professional line level is generally thought of as a signal whose level is at +4 dBu (1.23 volts or significantly higher). Ex: Signal-processing equipment and professional mixing consoles
How does instrument level compare to line level?
Instrument level sits between mic and line level, often noted as HiZ (high
impedance) on audio devices. These signals also need amplification.
Gain staging
On a mixing desk, both the mic preamp and channel fader can change the overall level of the sound before being sent to Master Fader or Aux Sends. (That’s four points of gain control)
Any point at which the signal level can be adjusted is a gain stage, including
equalisers
Where you reach a goldilocks level
Getting this right is crucial
Too much causes distortion, clipping, yucky. Too high, poor signal to noise (?)
What happens ff a gain stage is set to unity (marked as 0dB or ‘U’)
There is neither amplification nor
attenuation (loss of flux intensity throughout a medium) of the signal level
EQ Types
- Filters
- Shelving Eqs
- Bell EQs/parametric EQs/semi-parametric EQ
EQ Parameters
- Cuttoff Frequency
- Q, bandwidth
- Resonant frequency
High-pass/low-pass filters
Either the high-frequency or low-
frequency end of the spectrum can be filtered using a low-pass or high-pass filter.
* Two of these together give us a band-pass filter.
* Filters are used to cut sounds.* (Resonant peaks boost frequencies, but this is more common in digital filters or stand-alone EQ hardware)
What is high-pass/low-cut usually set at?
These are often set around 75/80 Hz. The Allen and Heath mixer is set to 100Hz.
* As most musical instruments do not produce these low bass frequencies, cutting them out of the signal can result in less noise, fewer transmitted vibrations from the mic stand and an
overall cleaner signal.
Use this to reduce pop, microphone noise, low-
end rumble
Shelving EQs
These are for the bass and treble ends of the frequency spectrum and can be
boosted or cut
Shelf EQ adjustment can
cut or boost frequencies
by -15dB or 15dB.
* There is a knob for both
high and low frequencies. (“HF” and “LF”)
Bell/Parametric/Semi-parametric EQs
These affect the midrange. Fully parametric EQs will have three
controls;
1. one for the gain of the EQ,
2. one for the frequency that is being cut or boosted
3. one for Q factor of the EQ, which determines the width of the frequencies affected
Auxilary Sends
The auxiliary sends on a desk allow us to take parallel sends of the signal, usually for monitoring or effect sends.
We use the term ‘monitoring’ to describe checking the signal at a certain point in the signal flow
Can also monitor visually, by using meters that give us a visual indication of a signal’s
strength
Effect Sends in monitoring
Would include artificial reverb or delay on the vocals, which would then
blended back into the mix.
Pre and Post fader auxiliaries
Pre-fader auxes mean that the signal level is independent of the channel fader.
* If you turn down the channel fader, the level to the aux will not be altered.
* This is useful for monitor sends, where you could turn down the vocals in the main speakers and this would not affect the level going to the vocalist’s monitor speaker
Difference between series and parallel path
In a series, the signal flows directly from one component to
the next.
In parallel, the signal is split into multiple signal paths
An audio signal path can be traced and ideally monitored at any point in the chain.
* Remember that every component in the chain can be a source of distortion (unwanted change to the signal) and
the most common of these is amplitude overload distortion. That is, the signal is too loud.
The Channel Fader
- The channel fader determines how much level is sent to busses or the main mix from that channel.
- If a mic level is set too low, the signal path will have a poor signal-to-noise ratio.
- If more gain is added later, the inherent noise within the system will also get amplified.
- If a mic level is set too high, the signal path will distort.
- Getting the microphone preamp level right is a very important part of both live sound and studio recording.
Balanced/Unbalanced connections
The two primary types of analogue connections,
* Balanced connections will have 3 points of contact (e.g. XLR), unbalanced cables have 2 (e.g. RCA)
points
Phase Cancellation in Balanced Cables
Balanced cables result in less noise over long cable runs
This is achieved by duplicating the signal, in two side by side wires within a cable, with
one out of phase to the other.
Any noise induced into the signal will then cancel out when the duplicate signal is
flipped back into phase at the termination of the cable run
Connector Types
TRS
aka 1/4” or 6.35mm or stereo jack
Tip Ring Sleeve
3-point connector
May be balanced or unbalanced
Can carry a mono balanced signal
Or
Stereo unbalanced signal
Effect processors, audio interfaces, instruments
——————-
TS
aka 1/4” or 6.35mm or mono jack
Tip Sleeve
2-point connector
Not balanced
Guitar or instrument cable
Direct Injection (DI) Box
- allow for instruments to be plugged directly into a mixing desk microphone input.
- For example: keyboards, samplers, bass guitars (if there’s no bass amp), laptop outputs, etc.
- DI boxes take a high level, unbalanced
instrument signal and convert it to a low level, balanced microphone signal that can be sent down a lead to the desk before being brought
back up to line level signal in the desk. - This helps reduce noise when the cable run is longer than a few meters, as low-level, balanced microphone signals are less susceptible to
induced noise than unbalanced line or
instrument level signals
