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Data cables

ADAT / lightpipe / optical; uses pulses of light down fibre optic cable. Supports up to 8 channels at 48kHz, 24 bit. Similar to S/PDIF (this sometimes uses phono connector).

Firewire; industry standard for data in studios / video work. Now a little dated, traditionally Mac specific. Was faster than USB until e.g. USB-C.

USB (Universal Serial Bus); industry standard for data. Used to connect interfaces to computers but also seen on peripherals e.g. mouse. MIDI often now uses USB.

MIDI / 5 pin DIN (musical instrument digital interface); used to connect synthesisers and other electronic instruments together. In / out / thru connectors. Data not audio.

Analogue / Audio cables

Phono / RCA; used for hi-fi / CD players / DJ mixers / consumer audio. Mono but stereo if there are two cables – white / black is left, red is right. Unbalanced so prone to hum / interference – also used for digital audio as S/PDIF.]

2egative and ground / hot, cold and neutral. Used for microphones / balanced line level / output of a DI box. They are analogue and mono; balanced so less noise over long runs.

Jack (TS/TRS); can be TS or TRS – used for guitars / line / DI box input. Analogue connection. TS = mono, TRS used for headphones etc… so often stereo. TS = unbalanced so susceptible to hum, TRS = balanced. Tip, ring, sleeve; tip carries signal.

Balanced cables

• XLR cables and TRS jacks are what we call balanced connectors
• This means that they cancel out noise picked up as part of the cable run
• An unbalanced cable contains two connections – a signal and a ground
• A balanced cable contains three connections: hot (+), cold (-) and a ground
• Both the hot and the cold connections carry a version of the signal
• The cold signal is a copy of the hot signal with the polarity flipped
• Noise is picked up equally on the hot and cold signals
• When both of the signals reach their destination, the polarity of the cold signal is flipped again
• Therefore, the signal is now in phase with the original but the cold noise is out of phase with / of opposite polarity to the hot noise
• Combining the hot and cold signals mean that the noise then completely cancels.

Preamps and DI boxes

• A preamp converts microphone level into a workable line level; they are used between microphones and mixers
• Mixers have preamps built in but many external (and more expensive) preamps can give vintage or analogue character to the part being recorded
• DI stands for ‘direct injection’; a DI box is used to connect unbalanced high impedance instrument signals (jack) to balanced microphone level signals (XLR) for connection to a mixing desk or audio interface.

Impedance

• We refer to microphone level, instrument level and line level; these have a difference in impedance (‘Z’)
• Microphone and instrument levels are much lower than line level (line level is around 1000 times greater than microphone level); this is most important when connecting different pieces of equipment together
• For example, connecting a line level source to a microphone level input will cause distortion because the signal is louder than the input is designed to accept.

Microphone level	Instrument level	Line level
Lowest level (‘lo-z’)	Slightly higher than microphone level (‘hi-z’)	Many times louder than both microphone and instrument level

Revision checklist

How leads work

Balanced and unbalanced connections

The different types and uses of leads

Jack

XLR

MIDI

Digital ins / outs

Computer data cables e.g. FireWire and USB

Using balanced connections to avoid noise e.g. hiss, hum and rumble

DI boxes

Impedance

Signal levels; mic, line and instrument

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