Introduction to Computer Music: Volume One

3. Mixing Console Basics | page 3

The EQ (equalization) section is used to adjust the amount of boost or cut (attenuation) for high, midrange and low frequency bands (the exact number of frequency bands varies according to the mixing console model). Certain mixers allow the user to adjust the exact frequency of the bands as well as their boost or cut. For example, on this mixer, notice that the low mid(range) section allows adjustment of the center frequency (lower pot) as well as the amount of boost or cut (upper pot). A common novice mistake is to twirl the lower know while leaving the upper knob set to zero, which will do absolutely nothing to the sound, since you are neither boosting nor cutting the frequencies you are adjusting.

The high mid(range) section of this mixer adds a third control (lowest knob) to the boost/cut and center frequency, namely the bandwidth (or Q), or frequency range of this section. Neither the lowest nor highest band is adjustable, just the amount of boost or cut. Both the high mid and low mid are peak/notch filters.

The Hi and Lo EQ use shelving filters, meaning that they boost or cut most frequencies above 12K (Hi) or below 80 Hz (Lo) equally. (Picture a horizontal shelf moving up or down without tilting.)

In addition, mixers may provide a high-pass or rumble button to eliminate unwanted low frequencies caused by vibrations on a mic stand, foot tapping, HVAC, etc. In this case, depressing the low cut button will roll off frequencies beginning at 75 Hz. Finally, be sure to depress the EQ IN button if you wish your EQ settings to have any effect. Toggling this button is a good way to ascertain the effect of your EQ on the sound vs. the original signal.

Equalize tracks separately before mixing down a multitrack recording. One caution, however, is that boosting or cutting frequencies will cause the input balances to change. Extreme boosting of frequencies, particularly in the low band, may cause a channel to distort, since it may add up to 15 dB of energy, more than four times the original strength.

To the left is the Mix-B section. Some mixers, such as the Mackie and Tascam line, have a separate bus of inputs for tape or line devices included on the channel inputs. The Mackie board on the left calls these Mix-B. Some boards use direct inserts instead. Both of these types of inputs usually bypass the input sensitivity pots, and so their level is expected to be in a standard -10 to +4 dB range. To balance variations in these levels, many studios use level-matching boxes. These inputs effectively double the number of board inputs, since they can be accessed simultaneously with a line or mic signal. So a 32-channel board can then actually mix 64 audio inputs.

The Pan pot for Mix-B controls the left/right or odd/even balance of the channel's output. A more thorough discussion of panning can be found on the next page.

The level knob to the left controls the gain of the Mix B inputs. However, if the source button is depressed, the function of this knob and the regular channel fader are swapped. This knob will then control the normal input gain of the channel, where the channel fader below will control the Mix B gain. If an expected signal is not audible, check the source button.

The Mackie also allows the Mix-B signal to go through the Hi/Lo EQ if the split EQ button is depressed.

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