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Gain structure

• Gain is how loud an input signal is before it enters the device; the higher the gain, the louder the signal
• If a mic has e.g. low sensitivity, you will need to turn up the gain so that the amplifier can make the sound louder
• When you are recording, you have to plug lots of different pieces of equipment together; each individual piece of equipment will have its own volume control
• Gain structure / gain staging is how loud each piece equipment of the recording chain is
• If you get your gain structure right, it means that you will use the dynamic range of audio equipment to its best advantage meaning that you will minimise both noise (when the signal is too quiet) and unwanted distortion (when it is too loud); to do this, it is necessary to set appropriate gain levels on each piece of equipment in the recording chain.

Signal to noise ratio

• The signal-to-noise ratio of a recording is how we describe the difference in volume between the signal you want to capture and the noise
• A poor / low signal-to-noise ratio means that noise is more prevalent in a recording
• Headroom is the space between the loudest peaks of your mix or audio and the point at which clipping begins
• The signal-to-noise ratio combined with the headroom gives the dynamic range.

Mono compatibility

• We hear stereo because of time differences between e.g. two microphones or two channels of audio
• Summing the left and right channels of a stereo mix means collapsing the stereo image into mono
• Timing differences mean that the signals between the left and right have a complex phase relationship
• Therefore, when mono summed, phase cancellation can occur, making the sound weak at some frequencies.

Stereo microphone techniques

• An XY (coincident) pair places two cardioid mics so the capsules are next to each other, combining their polar pattern; this captures a wider stereo image and maintains a good mono compatibility
• An AB (spaced) pair uses two omni mics placed around 50cm apart and is often used to record larger ensembles; the further apart the mics are, the less mono compatible they are and the bigger the hole in the middle
• An MS (mid-side) pair consists of a cardioid and figure-of-8 mic set up at 90^o to each other – the figure-of-8 mic captures the sides and the cardioid mic the centre; the width can be adjusted by turning up / down the figure-of-8 mic; in mono, the sides cancel.

Placing microphones

• A microphone placed off axis (at an angle to a source) captures a duller signal
• A microphone placed on axis (at 90 degrees to a source) captures a duller signal
• A microphone placed at the centre of the cone of a guitar amp will capture a brighter signal than when placed at the edge
• The further a mic is from a source, the more reverb that will be captured; there will be less impact from proximity effect (if the mic is directional)
• The closer a mic is to a source, the more proximity effect there will be (if the mic is directional) and the less reverb will be captured.

General capture advice

• Sibilant sounds can be a problem around 5kHz – 10kHz; a deesser reduces sibilance; careful with EQ HF boosts
• Use headphones for monitoring to avoid spill; keep them quiet to avoid the click coming through
• Acoustic treatment on walls reduces the room sound / reverb; baffle boards / screens separate instruments; listen carefully to background noise / spill at this stage and try to reduce rather than leaving it to fix later
• On / off-axis microphone placement needs consideration
• You need to be careful the instrumentalist isn’t moving around too much
• It helps to fix any noise from keys / squeaks etc… at the time – don’t think ‘fix it in the mix’
• Check the position of switches e.g. pad / polar pattern / HPF / phantom power / polarity on mics and interfaces.

What you need to know

Gain structure and how it affects noise and distortion

Setting gain to maximise signal-to-noise-ratio

Avoiding clipping

Avoiding hiss

Checking input and output levels when several effects / pieces of hardware are chained together

Microphone techniques

Single and multiple microphone techniques

Placement distance and angle

Managing spill and background noise

Eliminating plosives

Advanced microphone techniques

Coincident and spaced stereo pairs

Mid-side stereo recording and processing

The suitability of microphone placement techniques

Suitable distances and angles

Recording instruments using multiple microphones, e.g. drum kit

On-axis and off-axis frequency responses

Stereo

Mono summing

Mid-side processing

Mono compatibility

Advantages and disadvantages of different leads and connectivity

Comparing balanced and unbalanced connections

Comparing analogue and digital connections

Comparing computer data connections

Gain structure and how it affects noise and distortion

Controls on a pre-amp: phantom power, gain, pad, HPF, polarity, clip / activity