Getting the Source Mixers, Microphones, and Preamps Erik Scull

Mixers ▪Audio input/output routing (I/O) ▪Analog Mixers: Big, lots of knobs, faders, lights, and cables. Still common in commercial studios, but becoming scarce in project/home studios. ▪Digital Mixers: Perform same tasks as analog mixers, but with smaller footprint. Signal routing is often easier and more flexible. ▪Software Mixers: Included with audio recording software; all routing is done virtually inside the computer. Must use keyboard/mouse to manipulate virtual controls unless you have a… ▪Control Surface: A piece of hardware that, using MIDI, works with a software mixer to provide a tactile interface complete with faders, pots, etc.

Mixers: Inputs ▪Microphone ▪XLR (3 pin) ▪Preamp to boost level ▪Often with phantom power ▪Line/Instrument ▪¼-inch jack ▪Balanced or unbalanced (TS or TRS) ( ▪Hi-Z (High Impedance) ▪Designed for direct input of guitars, etc without the need for a DI (direct injection) box

Mixers: Input ▪Trim control: Adjusts the level of the signal entering the mixer. ▪Sometimes called Gain ▪Usually the top knob on a channel strip ▪Hard left for line level signals ▪Rotate clockwise to increase level for microphones

Mixers: Channel Strip ▪Analog Mixers: ▪Trim ▪Aux sends ▪EQ (parametric) ▪Pan ▪Mute/Solo ▪Subgroup assignments ▪Volume Fader

Mixers: Channel Strip ▪Digital/Software Mixers: ▪Input/Output selectors ▪Automation mode ▪Pan ▪Solo/Mute ▪Record enable ▪Volume Fader ▪Track type (audio, MIDI, etc) ▪Track Name

Mixers: Signal Flow ▪Signal moves from top to bottom: ▪Source audio input ▪Insert effects (external EQs, compressors, etc) ▪Pre-fader aux send(s) ▪Channel EQ ▪Pan ▪Solo/Mute ▪Volume Fader ▪Post-fader aux send(s) ▪Output (to main bus or submix bus)

Mixers: Routing ▪Bus = Audio pathway ▪Master bus: final mix ▪Submix bus: mix groups of tracks before going to master bus; drums are a common example where this is used ▪Auxiliary Bus: Often used to add effects before going to the master bus

Mixers: Outputs ▪Master L/R output ▪Headphone output ▪Monitor output ▪In computer-based systems, this sometimes used for “hardware monitoring”; that is, you can monitor directly from the audio input interface without the audio having to go into the computer and back out again. This can help mitigate latency issues.

Tracking: Signal Path ▪Sound often goes through several steps (and/or pieces of gear) before getting recorded. ▪The sound should be optimized at each step to ensure that you don’t have too much or too little signal getting to the recording step. ▪If signal is too high: distortion. ▪If signal is too low: noise.

Tracking: Signal Path ▪The key is to get as ‘hot’ a signal possible without going over the maximum that the recorder or converter can handle (causing clipping). ▪0dB refers to the highest level a digital system can handle without clipping. ▪Rule of thumb: ▪16-bit systems: peaks no higher than -6dB ▪24-bit systems: peaks no higher than -12dB

Tracking: Signal Path ▪Tips: ▪Keep an eye on the clip light of the preamp/input if there is one ▪Use meters as a guide ▪Trust your ears (meters can act too slow to catch some transients) ▪When in doubt, turn down. Recording a slightly lower signal won’t ruin a track, but clipping (even occasionally) can.

Microphones ▪Microphones and the preamps that bring their signals up to recordable levels are often referred to as the paints and paintbrushes of a sound engineer. ▪While many situations call for microphones to capture the source sound as accurately as possible, engineers often favor certain mic/preamp combinations due to the sonic characteristics they impart on the signal.

Microphones: Construction Types ▪Condenser: ▪Most popular for pro/home recordists ▪Relatively flat (accurate) frequency response ▪Fast response (captures transients: initial attack) ▪Can be expensive ▪Large-diaphragm Low-end response Low self noise ▪Small-diaphragm More accurately reproduce high frequencies ▪Require a battery or phantom power

Microphones: Construction Types ▪Dynamic: ▪Example: Shure SM57 and SM58 ▪Can handle high SPL (Sound Pressure Level) Drums Guitar amplifiers Some rock vocalists ▪Not as transparent as condenser mics; can impart a ‘dirtier’ sound due to accentuation of the middle frequencies.

Microphones: Construction Types ▪Ribbon: ▪Slower response to transients make for rounder, richer tone ▪Popular in the 1930s-1960s; condenser mics now more common. ▪The ribbons are fragile; high SPL or wind can cause damage ▪Experiencing a resurgence in popularity with engineers going for a ‘vintage’ sound.

Microphones: Polarity Patterns ▪Omidirectional ▪Picks up sound from all directions ▪Common uses: Drum kit overheads Groups of instruments (orchestras) Not generally used for close miking – less than a foot away (too much background noise)

Microphones: Polarity Patterns ▪Cardioid ▪Picks up sound from the front; rejects sound from the back. ▪Commonly used in close miking situations Vocals, instruments, amplifiers, etc. ▪Three sub-patterns: Cardioid, Super-cardioid, Hyper-cardioid (subtle differences in focus of the front pickup and rear rejection) ▪Proximity effect Some have bass roll-off switches to compensate

Microphones: Polarity Patterns ▪Figure-8 (Bidirectional) ▪Picks up sound from the front and rear ▪Commonly used to record two instruments simultaneously, facing each other ▪Ribbon mics are usually Figure-8 pattern ▪Multiple-pattern ▪Ability to switch between polarity patterns

Microphones: Common Applications ▪Vocals: Large-diaphragm condenser ▪Electric Guitar Amp: Dynamic or small-diaphragm condenser ▪Electric Bass Amp: Dynamic or large-diaphragm condenser ▪Acoustic guitar: Large- or small-diaphragm condenser ▪Brass/Woodwinds: Ribbon or large-diaphragm condenser ▪Piano: Large- or small-diaphragm condenser, depending on the room and mic placement ▪Drum set: Dynamic or large-diaphragm condenser ▪Cymbals: Pair of small-diaphragm condenser

Microphones: Links ▪ ▪

Microphone Preamps ▪Used to bring the microphone signal up to recordable (line) levels ▪Many mixers and audio interfaces have preamps built into one or more channels; however, these tend to be of lesser quality than stand alone units.

Microphone Preamps: Types ▪Solid state: ▪Uses transistors to boost the level ▪Typically designed to be clean and transparent, though they can be designed to add ‘dirt’ or ‘grit’ ▪This is the type found built into in mixers ▪Vacuum Tube: ▪Uses vacuum tubes to boost the level ▪Tend to add coloration to the sound ▪Hybrid: ▪Offers attributes of both solid state and tube preamps ▪Usually can adjust the amount of warm tube sound ▪More flexible; however, will not usually perform as well as a true solid state or tube preamp in their respective abilities

Microphone Preamps: Options ▪Some microphone preamps come with other features built in: ▪Compressor Used to control transients (initial attack of a sound) by altering the dynamic range of the sound making the overall input signal ‘hotter’ ▪Equalizer Used to shape the frequencies of the input signal

Microphone Techniques ▪Spot (close) miking: within inches of the source ▪Distant miking: a few feet away ▪Ambient miking: very far away ▪Stereo miking: two mics with various distance between them ▪Combined miking: Any combination of the above

Microphone Techniques ▪Spot (close) miking: ▪Transients are more extreme ▪The room isn’t a factor (good or bad) ▪Can isolate instruments ▪Minor adjustments in placement can have huge impact on sound ▪Proximity effect with cardioid mics

Microphone Techniques ▪Distant miking: ▪More natural sound ▪Instrument bleed ▪Room becomes a factor ▪Potential phase problems with more than one mic

Microphone Techniques ▪Ambient miking: ▪Lose attack ▪Requires a good room ▪Placement very important (sweet spot) ▪Potential phase problems with more than one mic

Microphone Techniques ▪Stereo miking: ▪X-Y pair of cardioid mics Not as wide a stereo field as real life Use sparingly Keep distance from source to preserve stereo effect Stereo mics often behave like an X-Y pair ▪X-Y pair of figure-8 mics (Blumlein technique) Two figure-8 mics, one on top of the other offset 90 degrees More neutral than cardioid X-Y pair; room is very important.

Microphone Techniques ▪Stereo miking (cont.): ▪Spaced pairs: Two mics, often omnidirectional. set apart from each other pointing at sound source Common for groups, ensembles ▪Mid/Side technique Omni or cardioid facing sound source, with figure-8 placed coincidently at 90°. Signals must be “decoded”, but decoding can be done manually. See: ▪