TRANSDUCERS
A Transducer is a device that converts energy from one form to another. Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal). Loudspeakers do the opposite ie; they convert electrical energy into acoustical energy. Analog tape machines are also transducers; they convert electrical energy into magnetic energy and back again. Without transducers, recording audio would not be possible.
MIC v LINE – WHICH INPUT TO USE?
The electrical signal generated by a microphone is tiny. This can be why some microphones appear to be ‘noisy’. A low output microphone requires a lot of amplification (gain or level boost) to reach a desired level for recording purposes. Different types of microphones have differing levels of output. Referred to as Mic Level, this signal is measured in millivolts and needs amplification before it can be successfully used or recorded. This ‘amplified’ signal is referred to as Line Level (0.5 -2V). This Line Level signal, being stronger, survives transmission through long cables much better than Mic Level and is ideal for distribution around studios and broadcasting stations. Line Level is the standard signal strength used by audio processing equipment, DAW’s, tape machines, etc.
Amplification of Mic Level is typically performed by Mic Preamps or if using a console, by the onboard mic amps in each channel.
UNBALANCED v BALANCED
Most domestic systems use Unbalanced interconnectors where there is only two conductors used, a centre wire or positive and a shield or negative. This is ok for short runs and where the signal level is robust. RCA / Phono cables are typically unbalanced. To interconnect professional equipment we use Balanced cabling and connectors. This means that there are two centre wires, a positive and a negative carrying the audio signal surrounded by a braided shield. The braided shield acts as a barrier to unwanted noise and interference. The two centre (opposed in polarity) signal wires can be summed at the destination in such a way as to cancel out any noise or interference picked up along the way. This is very useful particularly for long cable runs. It’s worth mentioning that XLR microphone cables and connectors are expected to carry 48 volt Phantom Power for Condenser Microphones or any microphones that have amplifiers built in and require power in order to function. If you look at the back panel of the Neve 1081 Preamp up above, you will see that all audio connectors are in the form of balanced XLR's. This is the norm for professional equipment.
IMPEDANCE
When connecting a microphone to a preamp or console, it's worth knowing a little about Impedance. Impedance is an electrical term that describes the amount of opposition to an AC current, in this case an audio signal. Like "resistance", it is measured in ohms and uses the symbol Ω (Greek Omega)
DIGITAL IN / OUT
A fab way of copying or transferring data from one device to another in a lossless manner. Digital Audio can be transmitted via various connectors and formats between domestic or professional equipment. The three main formats are AES for Professional use, SPDIF for domestic use and TOSLINK for both domestic and professional use. AES connectors are XLR or BNC, SPDIF connectors are Phono or RCA and TOSLINK is fibre optic. There is much more to Digital connectivity then we will discuss here but suffice to say that other data can be sent along the cables with the audio, including text and clock / timing information. For this reason one machine will be the "Master" and other connected equipment will be slave(s).
MIDI
MIDI (Musical Instrument Digital Interface) is a specification that enables a wide variety of digital musical instruments, computers and other related devices to connect and communicate with one another via three 5 pin DIN cables, ie., an IN an OUT and a THRU. Because the format is standardised, it guarantees compatibility between devices. MIDI equipment transmits note events as well as controls such as knobs, faders and buttons, encoding them as digital messages, and transmits these messages to other devices for playback. This data can be recorded into a sequencer or to a DAW, which can be used to edit the data and to play it back. MIDI can specify note event information such as velocity, duration, pitch, volume, vibrato, panning etc., and clock signals that can synchronize tempo and 'start times' between multiple devices. A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device if desired. MIDI helped bring about the electronic sounds of the 70’s in Pop music. Much of today’s music is ‘sequenced’ so that it’s unusual to hear a real band on a recording anymore! Drums, Bass and keyboards are usually produced using MIDI performances routed through samplers or ‘virtual’ software instruments.
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