Mackie M1200/M1400 owner manual shelving

Q

A way of stating the bandwidth of a filter or equalizer section. An EQ with a Q of .75 is broad and smooth, while a Q of 10 gives a nar- row, pointed response curve. To calculate the value of Q, you must know the center frequency of the EQ section and the frequencies at which the upper and lower skirts fall 3 dB below the level of the center frequency. Q equals the cen- ter frequency divided by the difference between the upper and lower –3 dB frequencies. A peak- ing EQ centered at 10kHz whose –3 dB points are 7.5kHz and 12.5kHz has a Q of 2.

TRS

Acronym for Tip-Ring-Sleeve, a scheme for connecting three conductors through a single plug or jack. 1⁄4" phone plugs and jacks and 1⁄8" mini phone plugs and jacks are commonly wired TRS. Since the plug or jack can carry two signals and a common ground, TRS connectors are often referred to as stereo or balanced plugs or jacks. Another common TRS applica- tion is for insert jacks, used for inserting an external processor into the signal path. In Mackie mixers, the tip is send, ring is return, and sleeve is ground.

RFI

Radio Frequency Interference. High frequency radiation that often results from sparking circuits. This can be manifested in a number of ways in audio systems, but is usually evident as a high-frequency buzz or hash sound.

RMS

An acronym for root mean square, a conven- tional way to measure AC voltage and audio signal voltage. Most AC voltmeters are cali- brated to read RMS volts. Other conventions include average volts, peak volts, and peak-to- peak volts.

shelving

A term used to describe the shape of an equalizer’s frequency response. A shelving equalizer’s response begins to rise (or fall) at some frequency and continues to fall (or rise) until it reaches the shelf frequency, at which point the response curve flattens out and re- mains flat to the limits of audibility. If you were to graph the response, it would look like a shelf. At least, more like a shelf than a hiking boot. The EQ controls on your stereo are usu- ally shelving equalizers. See also peaking and dipping.

TS

Acronym for Tip-Sleeve, a scheme for con- necting two conductors through a single plug or jack. 1⁄4" phone plugs and jacks and 1⁄8" mini phone plugs and jacks are commonly wired TS. Sometimes called mono or unbal- anced plugs or jacks. A 1⁄4" TS phone plug or jack is also called a standard phone plug or jack.

unbalanced

An electrical circuit in which the two legs of the circuit are not balanced with respect to ground. Usually, one leg will be held at ground potential. Unbalanced circuit connections re- quire only two conductors (signal “hot” and ground). Unbalanced audio circuitry is less expensive to build but under certain circum- stances is more susceptible to picking up noise.

unity gain

A circuit or system that has its voltage gain adjusted to be one, or unity. A signal will leave a unity gain circuit at the same level at which it entered. In Mackie mixers, unity gain is achieved by setting all variable controls to the marked “U” setting. Mackie mixers are opti- mized for best headroom and noise figures at unity gain.

stereo

Believe it or not, stereo comes from a Greek word that means solid. We use stereo or stereo- phonic to describe the illusion of a continuous, spacious soundfield that is seemingly spread around the listener by two or more related au- dio signals. In practice, stereo often is taken to simply mean two channels.

sweep EQ

An equalizer that allows you to “sweep” or

continuously vary the affected frequency of one or more sections.

volume

Electrical or sound level in an audio system. Perhaps the only thing that some bands have too much of.

XLR connector

A three-pin connector used in audio for transmitting a balanced signal. Sometimes re- ferred to as a Cannon connector, named for the manufacturer who first popularized the three- pin connector.

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