Audio Engineering Principles - by Moses

 Audio Engineering Principles

 1) dbu vs dbSPL
     
 2) Crossover Points

 3) Variable Gain Amplifiers (V.G.A’s)

 4) Equalization Sections

 5) Band-Pass Filters

 6) Monitors

 7) Microphones and Mic Polar Patterns

 8) Compressors and Limiters

 9) Gates and Expanders
                       
 10) Reverb, Delay, and the Haas Zone (the Precedence Effect)
                     
                                                        
1. dbu vs dbSPL

      To double your dbu simply raise 3 dbu (+3dbu).
To double your dbSPL you raise 6 dbSPL (+6dbSPL).
  dbu is doubled (+3dbu) with each wall/floor/ceiling.
dbSPL is doubled (+6dbSPL) with each wall/floor/ceiling.
  dbu refers to the mixers output from the mains (Left and Right) to the multi-track (recording device).  Most analog mixers max-out at +6dbu (the good ones max-out at +10dbu).  On digital mixers you automatically max-out at 0 dbu.
  DbSPL refers to the amplitude of the sound that comes out of the monitors (the speakers).  Sound at outdoor concerts and arena concerts usually measure in the 100-120 DbSPL range.

2. Crossover Points

      A speaker cabinet with one crossover point is a two-way.
A speaker with two crossover points is a three-way.
A crossover point sends the frequencies above that point (or frequency) to one section of the speaker and frequencies below that point to another section of the speaker cabinet, before amplification. 

3. Variable Gain Amplifiers (V.G.A’s)

Saw-Tooth Wave – Gives a saw-tooth pattern to the frequencies and amplifies them.
Triangle Wave – Gives a triangular pattern to the frequencies and amplifies them.
Square Wave– Gives a square-pattern to the frequencies and amplifies them.  
Exciters – Are a glorified V.G.A.  Boosts certain high-end har0monics.
Flanging, Phasing, Chorusing and Delay are the results of a V.G.A device.

4. Equalization Sections

      Parametric Equalization – Carries three qualities:

Frequency (set frequency measured by Hz).
ii)      ‘Q’ or Slope (how severe a boost or cut).
Amplification.

      Graphic Equalization – Carries two qualities:

A certain number of set frequencies (A 30 Band Graphic E.Q strip has 30 set frequencies – which are measured in Hz).
The dbu (amplification level).

5. Band-Pass Filters (Guard-bands)

High Pass Filters – Allows high frequencies to pass above a certain frequency and cuts those frequencies below that frequency/likewise Amplitude Levels.
Low-Pass Filters – Allows low frequencies to pass below a certain frequency and cuts those frequencies above it/likewise Amplitude Levels.
Filter Designs: 1) Chebeshev, 2) Bessel, 3) Butterworth, 4) Gaussian
Main Supplier: Gemen

6. Monitors

Nearfield – Small monitors used in most control rooms of recording studios (usually NS10’s or Alesis).  Gages the mix with high frequency bias.

Midfield – Mid-sized monitors used in many live shows at the Bar/Pub.  Has a bigger base drum in the speaker than a nearfield.  Typically used as mains in the control room to complement NS10’s (usually Tannoy or J.B.L).

Farfield – Carries the best fidelity of the three.  It’s the largest speaker cabinet.  Used for outdoor concerts and arena concerts as well.  Usually carries a bass drum of a minimum 18’’ and has two crossover points (minimum).

Lesley Cabinet Speaker – A Farfield monitor that plays from a cabinet speaker that goes around and a-around.  Is reminiscent of a vinyl player (a phonograph).

7. Microphones and Microphone Polar Patterns

Microphones

Dynamic Microphones – Direct current from the mic into the mic panel (mic in).  This enables the mic to the mic-pre-amp for setting the mic level in the channel. Well known dynamic mics include Shure 57’s and 58’s.

Condenser Microphones – Condenser microphones connect to the mic panel (mic in).  At the start of the I/O Module you must give Phantom Power to prompt a response from a condenser microphone.  You then use the mic-pre-amp to set the level for the channel.  Known condenser mic’s include Neumann U87 and U47, AKG 414 and Silver Pencils (made by Sennheiser).

Microphone Polar Patterns

Uni-Directional – Mic takes in from only one direction on the mic.

Bi-Directional – Mic takes in sound from two directions on the mic, usually at opposite sides.

Omni-Directional – Mic takes in sound all around the diameter of the mic.

Cardioid – Heart shaped diameter that is sensitive to the sounds penetrating in the cavity.

Hyper-Cardioid – Instead of being a heart shape there is an oblong piece placed inside a cardiod shape (heart shape – inside the cavity).

8. Compressors and Limiters (Guard-bands)

      Compressors take in a certain amplitude (measured in dbu or dbSPL) and outputs at a lower amplitude by ratio.
 For example – A 1:1 ratio means that for every 1 db in there is 1 db out.
A 2:1 ratio means that for every 2db-in there is 1db-out.
A 4:1 ratio means that for every 4db-in there is 1db-out.
      A limiter is essentially a severe compressor.  In other words, it will cut the signal if the amplitude is too loud.  

9. Gates and Expanders (Guard-bands)

      A gate allows the microphone to be on only above a certain amplitude.  For example; If the gate is set at 60dbSPL that means that the microphone won’t be transmitting any signal below 60dbSPL but will transmit any signal 60dbSPL and up.
      An expander will take a certain amplitude in and output it at the same or greater level.  It works the opposite as a compressor.
A 1:1 ratio means that for every 1dbu-in there is 1dbu-out.
A 1:2 ratio means that for every 1dbu-in there are 2dbu-out.
A 1:4 ratio means that for every 1dbu-in there are 4dbu-out.

10. Reverb, Delay, and the Haas Zone (Precedence Effect)

Reverb – When the channel’s ‘spacial’ intonations are changed.  We’re looking at a very subtle change that effects where the music seems to be playing in (whether that be in a cathedral, arena, or amphitheater.  

Delay – Echo and Precedence Effect is the result of a sound repeating itself.  The Haas Zone (Precedence Effect) – Known to be a subtle delay (anywhere between 5ms – 35ms).  In this delay period the sound is played through the one side monitor anywhere between 5ms-35ms after the first side played.  This emphasizes the first sound and makes it seem to appear to be the louder of the two sounds, when in actual fact both sounds were at the same level.  This is known as ‘precedence effect’.