Introduction

Many types of connection leads and transmission protocols are used in the sound recording studio. Some of these leads can be used for multiple purposes and to carry different types of analogue and digital signal. Here are some of the most common ones ...

Name of lead	Signal type	Connector	Cable type	Typical uses
XLR / Mic cable	Mono balanced analogue microphone level audio (low amplitude), with phantom power.	XLR (canon).	3 cores. For analogue signals, X=external/earth, L=Live/hot, R=Return/cold).	To connect an analogue microphone to a mic pre-amp or mixer.To connect a DI box (guitar?) to a mixer.
	Mono balanced analogue line level audio (high amplitude).	XLR (canon).	3 cores. For analogue signals, X=external/earth, L=Live/hot, R=Return/cold).	To connect a professional tape recorder to a mixing desk.To connect a professional effect unit or dynamic processor to a mixing desk.To connect professional 2 tracks (tape, DAT, CD players etc).To connect a professional SMPTE device to a tape recorder.
	AES3 digital (mono/stereo unbalanced, up to 24-bit/96KHz). Originally known as AES/EBU. Identical data to AES-id. 7volts.	XLR (canon).	3 cores. 110 Ω twisted pair cable used	To connect 2 professional devices with a balanced digital signal (AES/EBU).
	AES42 digital microphone signal.	XLR (canon).	3 cores.	To connect an digital microphone to a digital mic pre-amp or mixer.
Balanced jack lead	Mono balanced analogue line level.	1/4" stereo jack.	3 cores (live, return, earth).	To connect a semi-pro tape recorder to a mixing desk.To connect a semi-pro effect unit or dynamic processor to a mixing desk.To connect semi-pro 2 tracks (tape, DAT, CD players etc)To connect a SMPTE device to a recording device.
Headphone lead	Stereo unbalanced analogue headphone level.	1/4" stereo jack.	3 cores (left, right, earth).	To connect headphones.
Unbalanced jack lead	Mono unbalanced analogue line level.	1/4" mono jack.	2 cores (live, return/earth).	To connect a keyboard, sound module, sampler, drum machine etc to an audio interface or mixing desk.To connect a guitar or bass to an amplifier or DI box. To connect a consumer tape recorder to a mixing desk.To connect a consumer effect unit or dynamic processor to a mixing desk.To connect consumer 2 tracks (iPod, MiniDisk, DAT, CD players etc)To connect a SMPTE device to a recording device.
Phono lead	Mono unbalanced analogue line level.	Phono plug	2 cores (live, return/earth).	To connect domestic consumer audio devices ((iPod, MiniDisk, CD players etc).
	S/PDIF digital (mono/stereo up to 24-bit 48KHz). 0.7volts.	Phono plug (known as coaxial RCA when used for S/PDIF)	2 cores (live, return/earth). 75 Ω cable used	To digitally interconnect domestic consumer and semi-pro audio devices.
Record deck lead	Stereo unbalanced analogue phono level.	2 x phono plugs and earth lead.	5 cores (left-live, return/earth, right-live, return/earth, seperate earth).	To connect a record deck to a phono pre-amplifier (or DJ mixer)
MIDI lead	MIDI / computer level (very low amplitude).	5 pin DIN	3 cores including shield	MIDI device interconnection. To transmit MIDI performance and system messages (eg between a synthesiser and a sound module)
USB	MIDI and digital audio / computer level (very low amplitude).	USB.	4 cores.	To connect a controller keyboard (MIDI) to computer.To connect semi-pro audio/MIDI interfaces to a DAW. To connect semi-pro FX and processor units to DAWs. etc
Firewire	MIDI and digital audio / computer level (very low amplitude).	FireWire.	6 cores.	To connect an audio/MIDI interface to a computer. DSP racks/farms to computers. Digital mixers to computers. etc
Optical S/PDIF	S/PDIF digital (mono/stereo optical/digital, up to 24-bit 48KHz).	Toslink.	Fiber-optic	Mono or stereo consumer and semi-pro interconnection, for example between a CD player and a DAT recorder, or an effects processor and a digital mixer (send/return).ADAT 8 channel digital interconnection, typically from a device such as a voice channel or mixer to an audio interface.
Optical ADAT	ADAT digital (8-channels of 24-bit 48KHz optical/digital).	Toslink.	Fiber-optic	To connect semi-pro/pro devices such as digital mixing desks and DAWs.
BNC	AES3-id digital (mono/stereo, up to 24-bit/96KHz).). Data is identical to AES3.	BNC.	2 cores.	Stereo professional interconnection such as the digital out from a mic pre-amp to a digital mixing desk.
	MADI - Multi-channel Audio Digital Interface (up to 56 channels of 24-bit 96KHz digital audio)	BNC.	2 cores.	Professional digital multitrack to large format digital mixing desk.
	MADI-X Multi-channel Audio Digital Interface (up to 64 channels of 24-bit 96KHz digital audio)	BNC.	2 cores.	Live sound / broadcast /recording applications.
Cat5/6	Ethersound (Digigrams's popular format)	RJ-45 ethernet.	8 cores.	To connect nodes in a distributed audio processing system (eg several Macs can acts as processing nodes for a Logic system).
	SuperMAC (48 digital audio channels)	RJ-45 ethernet.	8 cores.	Sony invented audio networking system.
	HyperMAC (384 digital audio channels)	RJ-45 ethernet.	8 cores.	Sony invented audio networking system.

 

Cost implications

As you can see, there are many types of connecting lead used for these different types of signal. Some signals can be sent down several different types of lead. It is worth remembering that equipment manufacturers will often choose a lead/connector type based on cost rather than robustness. Also some leads do not need to be strong. Phono leads which are often used to connect hi-fi are cheap and cheerful but are usually connected once and then left alone. Guitar leads will be plugged and unplugged many times and must therefore be reasonably strong.

Balanced and unbalanced

Many analogue (and some digital) leads employ 1 of 2 types of internal wiring arrangements. They are known as Unbalanced and Balanced.

Unbalanced

The unbalanced lead employs a cable with two wires, an inner insulated Live wire which is surrounded by a braided Earth wire which is itself protected by an outer insulation.The audio is sent down the Live wire. The Earth wire shields the Live wire from unwanted radio wave interference.

The Live wire may also be referred to as ...

• Send
• Positive
• Hot

The Earth wire may also be referred to as ...

• Screen
• Shield
• Ground

The unbalanced lead has 3 disadvantages ...

1. If the lead is too long the earth will be unable to stop some interference getting into the audio wire.
2. If the lead is too long there will be a certain amount of audio signal loss mainly in the higher frequencies.
3. It cannot carry Phantom Power.

For these reasons, the unbalanced lead is unsuitable for carrying Mic level signals which are quiet/weak and need extra protection.

In the studio the unbalanced lead terminate in 1 of 2 types of connector ...

1. Phono plugs

2. 1/4" (mono) jack plugs

Balanced

The balanced lead carries a "professional" quality signal and employs a cable with three wires. These are Live, Return and Earth. The audio is sent down the Live wire and is returned through the Return wire. The Earth wire just shields the Live and Return wires from unwanted radio wave interference.

The Return wire may also be referred to as ...

• Negative
• Cold

The balanced lead has 3 advantages ...

• In long leads high frequency audio loss is reduced.
• Interference from radio waves is completely eliminated in leads of all lengths.
• A balanced lead can carry Phantom Power to a microphone or D.I. (Direct Injection) box.

 

In the studio the balanced lead terminate in 1 of 3 types of connector ...

1. XLR (Canon)

Employs three pins: X (eXternal) = pin 1. L (Live) = pin 2. R (Return) = pin 3.

2. 1/4" (stereo) jack plugs

3. Bantam jack plugs

Used to connect patch leads between sockets on a professional patchbay.

How does a balanced lead eliminate interference?

The balanced lead works by using a system called Common Mode Rejection explained in the following diagram.

Stereo & mono signals

Analogue leads

In the sound recording studio almost all analogue leads carry a single mono signal. To connect a device in stereo you must therefore use 2 mono leads (left and right).

There is 1 exception ...

• Headphone leads carry a stereo unbalanced signal down a single cable that uses a 1/4Ó (stereo) jack plug

Digital leads

Because digital signals can encode multiple channels in a single signal only one lead is required to carry mono, stereo and multi-channel signals. Examples include ...

• A mic lead (XLR), carrying an AES/EBU 2 channel signal
• A carrying phono lead, carrying an S/PDIF 2 channel signal
• A Toslink optical lead, carrying an 8 channels ADAT signal
• A BNC lead, carrying a 56 channel MADI signal

NOTE: You may also want to read about digital audio synchronisation.

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