High and low shelf equalisers affect the high or low frequencies, respectively, raising  or lower the level of all frequencies in the corresponding band by the same amount. Consequently, the frequency response looks a bit like a shelf above or below the rest of the audio band. Sometimes also known as bass and treble tone controls.

Alan Dower Blumlein (1903-1942) was an electronics engineer who was instrumental in the development of stereo recording techniques and equipment in the 1930s when working for EMI. 

See Low-Pass Filter

See High-Pass Filter

A filter which passes frequencies below its cut-off frequency, but attenuates higher frequencies. Also known as a 'high-cut' filter.

seeCapacitor Microphone

A means of convenying information on a carrier wave by varying its instantaneous amplitude. In an audio application, like AM radio, the wanted audio signal's amplitude is used to create corresponding deviations in the carrier wave's amplitude.  A demodulator can detect these deviations and thus recover the base-band audio signal. This form of modulation contrasts with frequency modulation (FM) where the carrier wave's amplitude remains constant but its frequency is varied to convey the wanted signal.

A means of convenying information on a carrier wave by varying its instantaneous frequency. In an audio application, like FM radio, the wanted audio signal's amplitude is used to create corresponding deviations in the carrier wave's frequency.  A demodulator can detect these frequency deviations and convert them back to amplitude variations to recover the base-band audio signal. This form of modulation contrasts with amplitude modulation (AM) where the carrier wave frequency remains constant and its amplitude is varied to convey the wanted signal.

Most Capacitor microphones work by storing a static charge within the capacitive capsule. The traditional way of building up that static charge is by applying an external DC voltage, and this is known as a DC-Bias. Typically, the voltage is around 60VDC, but greater voltages permit more headroom, and altering the voltage can also vary the sensitivity of the capsule which is useful in configuring multi-pattern mics. The most common alternative to DC-Bias is the Electret design where the static charge is provided by a dielectric material built into the mic itself. A third alternative is the RF-bias technique which works on a different principle altogether.