Mackie PPM1012 owner manual Gain Control, LOW CUT Channels 1-8 only, Ing levels

23. GAIN CONTROL

If you haven’t already, please read the level-setting procedure on page 3.

If the signal originates through the

XLR jack of a mono channel (1 to 8), there will be 0 dB of gain with the knob fully down, ramping to 50 dB of gain fully up.

Through the 1⁄4" input, there is 20 dB of attenuation fully down and 30 dB of gain fully up (20 dB on ste- reo channels), with unity gain at 12:00. This 20 dB of attenuation can be very handy when you are inserting a very hot signal, or when you want to add a lot of EQ gain, or both. Without this “virtual pad,” this scenario might lead to channel clipping and distortion.

Clipping occurs when the peaks of the audio

signal passing through the preamplifier are

too high, and can no longer be amplified in a linear way. The audio signals reach a point

just below the preamp's supply voltages, and flatten out. This is rather like a tall pointed volcano suddenly blow- ing its top, leaving behind a lower flatter top (clipped) while thousands of tons of molten rock and ashes are blasted into the earth's atmosphere to cause a kind of global winter for thousands of years, leading to the dis- appearance of the dinosaurs and the appearance of jazz drummers. Only not. Adjust the gain to prevent this.

24. LOW CUT (Channels 1–8 only)

The mono channels each have a low-cut switch, often referred to as a high-pass filter (all depends on how you look at it). When engaged, this cuts the bass frequen- cies below 100 Hz at a rate of 18 dB per octave. The mic and line inputs of channels 1–8 are affected.

We recommend that you use low-cut on every micro- phone application except kick drum, bass guitar, or bassy synth patches. These aside, there isn’t much down there that you want to hear, and filtering it out makes the low stuff you do want much more crisp and tasty. Not only that, but low-cut can help reduce the possibili- ty of feedback in live situations, and it helps to conserve amplifier power.

Another way to consider low-cut’s function is that it actually adds flexibility during live performances. With the addition of low-cut, you can safely use low equaliza- tion on vocals. Many times, bass shelving EQ can really benefit voices. Trouble is, adding low EQ also boosts stage rumble, mic handling clunks and breath pops from way-down low. Applying low-cut removes all those problems, so you can add low EQ without losing a woofer out the window.