A Basic Understanding of Equalisation

What Equalisation is and How to Begin Utilising it

EQ is a tool that mixing engineers use to help balance a track in the mix. An EQ allows you to boost and reduce frequencies of a certain track, this could be to eliminate unwanted or unused frequencies or to put emphasis on desired frequencies. EQ's can be in software or outboard form and many mixing consoles have at least some level basic EQ control on each track. Although there many different forms of EQ, such as fixed and graphic which wont be touched upon in this post, they all do the same job. 

Understanding the Graph on a Parametric Equaliser

Although an EQ's graph may look confusing it is easy to understand. On the X axis runs frequency (Hz), usually only through the human hearing scale and on the Y- axis is dB. An increase of dB boosts the frequency and vice versa.

The Basic Parameters of a Typical Parametric Equalisation Unit

In order to fully understand how to operate an EQ, the parameters must be explained. In the image above is Pro Tools built in Parametric EQ unit, although visually different to others the basic controls stay the same throughout all EQ's. The first basic controls at the top are input and output, these simply control the level the track is when it goes in and its level when it leaves the effect. After this we arrive at HPF and LPF, these stand for high and low pass filters. Applying a high pass filter to a track would only let the high frequencies through, this is assuming it is on the highest dB Q and vice versa for low pass. You can control the amount of filter both the frequency and Q controls.

Frequency on a high or low pass filter controls up to which frequency the filter will effect. This is seen in the image to the left.














After the frequency control has been chosen the 'Q' controls how steep a roll off the filter has. (How quickly from the selected frequency does it completely stop sound passing).

Underneath the HPF and LPF controls are the parameters to go into greater detail in frequency manipulation. All these five parameters have essentially the same controls. Pro Tools just assign different colours and controls to different frequency groups so editing can be done to multiple parts of the frequency spectrum and the controls are not easily confused. In this example I am going to use the LMF parameter (low mid frequencies).


Frequency, again controls the specific frequency you are aiming to target.

The orange dot swivels across the spectrum to identify the chosen frequency.

The gain controls the boost or cut to the frequency, positive being boost and minus cut.



















Then finally Q in this instance controls how accurate the boost is, how many frequencies it will effect. 10 is the most accurate and 1 is the least.

Important Things to Note: This is only a guide to the very basics of EQ and is only aimed at giving a quick overview of the effect. Kinds of filters, such as shelving and peaking and their creative uses will be explained in a pending post. In addition, as already explained other soft parametric EQ's may differ in appearance and structure but the fundamental parameters will be the same. 

Phantom Power or 48V - The Basics

Why Do Some Microphones Need Phantom Power?

Phantom power is needed to charge the electric plate in condensers to enable it to create an alternating current (refer back to how microphones work). However there are some ribbon microphones that will need it too. As a general rule you can tell if a microphone needs phantom power by reading its specs. All condenser microphones apart from electret ones need phantom power. Applying phantom power to a microphone that doesn't need it however could end with disastrous consequences!

To apply phantom power to a microphone is fairly straight forward. On the audio interface or mixing desk the microphone is plugged into look for a button that say Phantom Power or just '+48v' and press it for the input the microphone is plugged into. If the interface has a general button for phantom power make sure that none of the other microphones that are inputed will suffer if they come into contact with it!

  

Image: http://www.realtimeaudio.ca/images/blog/avalon-vt-737sp-phantom-power-button.jpg

Characteristics of the Main Microphone Types - The Basics

The Dynamic Microphone 

- Generally have a slower transient response and lower sensitivity to more subtle sounds, this is largely down to their heavy moving parts

- Suffer from a general limited frequency range especially in the top end of the frequency spectrum

- More durable and robust then other types, this makes them a good choice for gigs

- Low levels of sensitivity (mV/Pa) means they are good for high impact and loud sound sources

- High SPL tolerance levels, this also makes them a safe option for a louder sound

The Condenser Microphone  

- Generally have a faster response rate to transients which gives a harder sound, lighter moving parts

- Tend to offer a broader Frequency response then Dynamics

- Require phantom power to work

- Higher sensitivity means they are able to pick up quieter sounds and be placed further away from the sound

- High Sensitivity also means they usually have a prominent proximity effect 

- Usually they are unable to handle high levels of SPL and are physically more fragile too

The Ribbon Microphone

- Generally fast response rate to transients and good at picking up subtleties 

- Give a 'warm' tone as they have a limited high frequency response

- Can require phantom power but usually don't 

- Very, very fragile - usually not suited to high levels of SPL

- Proximity effect can increase bass response if sound source is close

Reference - Ferreira, CL (2013). Music Production: Recording. Burlington: Focal Press. p17-22.

Images (Top to Bottom): 
- http://www.simplifiedevents.co.uk/wp-content/uploads/2014/03/BETA57.jpg
- http://www.dv247.com/assets/products/61034_l.jpg
- http://www.proaudiodesign.com/image.php?type=P&id=1088

How the Main Types of Microphones Work - The Basics

Introduction

Microphones come in a variety of different shapes and sizes but they also have different ways in which they convert acoustic sound into an audio signal. All microphones are transducers, they convert acoustic energy into an alternating current (AC).  

Dynamic Microphones 

Dynamic Microphones work in the opposite way to speaker cones. They are made up of a stiff diaphragm with a finely wrapped wire core. The wire is suspended precisely within a high level magnetic field. (Huber and Runstein, 2014) When the air pressure hits the diaphragm, the coil moves linear to the amount and frequency of the air pressure. This in turn causes the coil to cut across magnetic flux, caused by the permanent magnet. (Huber and Runstein, 2014) This creates an electrical signal, AC that mirrors that of the original acoustic sound wave and this is sent down the output wires.

Ribbon Microphones 

Ribbon microphones also work with electro magnetic induction. However they consist of an extremely thin strip of corrugated aluminium is suspended between two permanent magnets. When the sound pressure enters the microphone it causes the aluminium to move and this in turn induces the magnets, again replicating the acoustic wave through an AC current.

Condenser Microphones 

Condenser Microphones operate on the electrostatic principle. The capsule consists of two diaphragms a thin movable one and one fixed to the backplate. These form a condenser, an electrical device capable of holding an electric charge. (Huber and Runstein, 2014) When sound pressure is applied to a condenser the thin diaphragm moves causing the distance between the two diaphragms to fluctuate. This recreates the motion of the acoustic wave and is sent as an AC current through the output. 

Magnetic Flux - the amount of a magnetic field passing through a surface

AC - Alternating Current goes between plus and minus poles recreating the compression and rarefaction of an acoustical sound wave

References - Huber, DM Runstein, RE (2014). Modern Recording Techniques. 8th ed. Burlington: Focal Press. p110-113 

  

Understanding a Microphones Frequency Capabilities and Response - The Basics

Frequency Capabilities of a Microphone

All microphones have a certain frequency range that they are able to pick up. It is largely accepted that the average human hearing has a frequency range of 20Hz to 20KHz, sounds below or above this we are not able to audibly detect. A microphones frequency range can usually be found out on the manufacturers website in the microphones specifications section. For example a Shure SM57 can pick up frequencies between 40Hz to 15KHz (Shure, 2009-2015) Where as a Nuemann U87 Ai can pick up between 20Hz to 20Khz. (Nuemann, n/a) Although both microphones have there different uses in terms of overall capture the U87 Ai would give the most accurate results without other figures taken into consideration. 

Frequency Response Graphs 

Frequency response graphs show how the microphone reacts at certain frequencies.  As seen in the diagram to the right of the Shure SM57's frequency response. This graph is made by sweeping a constant on axis input signal through the whole frequency range. (Huber and Runstein, 2014) Think of the graph like an equaliser except the boosts and cuts in frequency are predetermined by the microphone itself. If we look again at the diagram it shows us that the SM57 is at its flattest at around 1KHz, gives a boost in response after around 3KHz and has a roll off after around 10KHz and below around 200Hz.  So in conclusion the most accurate to life signal from the Shure SM57 is between 200Hz to 1Khz.

References:

• Huber, DM Runstein, RE (2014). Modern Recording Techniques. 8th ed. Burlington: Focal Press. p121.
• Neumann. (N/A). Switchable Studio Microphone U 87 Ai. Available: https://www.neumann.com/?lang=en&id=current_microphones&cid=u87_data. Last accessed 18th Feb 2015.
• Shure. (2009-2015). SM57 Dynamic Instrument Microphone. Available: http://www.shure.co.uk/products/microphones/sm57. Last accessed 18th Feb 2015.

Image from: http://www.sweetwater.com/insync/media/2013/05/freq.jpg

Polar Patterns - The Basics

Introduction

Polar patterns, in the simplest terms, are where sound is picked up from on a microphone. The reason polar patterns are important to take into consideration when choosing the appropriate microphone is because each pattern has its own advantages and disadvantages in certain situations. This is a basic list of the most common polar patterns microphones have.

Cardioid 

This is the most common polar pattern. It's used for directional applications when there is a direct source to record and minimal background noise is wanted. This pattern, as seen in the diagram picks up most of its sound through the tip, or in some cases front of the microphone, but also picks up a smaller amount of sound from the sides too.

Bidirectional or Figure of 8

Bidirectional polar patterns are largely self explanatory. They except sound from two sides of the microphone but reject sound from all other parts. This Pattern can be useful for capturing room noise whilst recording in a nice room, picking up a duet if separation is not required and recording a guitarist and singer if the two transducers are placed above one another. (Ferreira, 2013)

Omnidirectional 

Omni means all and therefore, a polar of omnidirectional means the microphone picks up sound from every angle equally. The uses for this in recording include; background vocals, room ambiance and capturing orchestras and large choirs. (Ferreira, 2013)  

References - Ferreira, CL (2013). Music Production: Recording. Burlington: Focal Press. p33-34.

Links to images (top to bottom) 

• http://www.voiceactingmastery.com/wp-content/uploads/2011/11/Cardioid-Polar-Pattern-500x500.png
•         https://microphones.audiolinks.com/Microphones/Pickup/pickuppics200x300/bidirectionalnew.jpg
• http://www.voiceactingmastery.com/wp-content/uploads/2011/11/Omnidirectional-Polar-Pattern-500x500.png

Understanding Microphone Sensitivity

When buying a new microphone, or even choosing between existing microphones, it is important to always take the microphones sensitivity into consideration. The sensitivity should be matched to the application you are using the microphone for. Lets say you wanted to record an isolated snare, the thing you would be looking for in this case would be a Microphone with a low sensitivity rating. This is because, the greater the sensitivity the more sound the microphone will pick up. So if you wanted a low amount of "bleed" a lower sensitivity mic would be the most appropriate choice. On the opposite end of the spectrum, recording an acoustic guitar with a microphone with a low sensitivity level could sound weak and dull. In this case high sensitivity is needed to capture all the detail of the sound as it is more complex.
Sensitivity is usually measured in mV/Pa this is an abbreviation of Millivolts/Pascal. Millivolts is a small measurement of voltage (1/1,000) and  Pascal is a universally recognised figure of 94 dB SPL. It basically measures the output voltage of the microphone at the 3 pin connectors. This means if on a microphones specifications sheet it says 10mV/Pa, this simply means that at 94 dB SPL (1 Pascal) the microphone is emitting 10 millivolts. So in conclusion, the higher the value of mV/Pa the more output voltage the microphone has and therefore the more sensitive the microphone will be.

SPL - Sound Pressure Levels, this is what occurs when sound is created. The louder the sound the higher the sound pressure level (130 dB SPL = Threshold of Pain)