Setting Volume Levels


All of Logic's audio channel strips have a level meter that displays the channel's volume in decibels (dB). The bottom of this meter represents a dB value of (that is, silence), while the top of the meter represents 0 dB, which is the maximum allowable volume level before the signal clips the channel. As the level meter pulses up and down, the peak level is held for a few seconds, so you have time to see its value. The numerical value of the peak level is also displayed in the clip detector at the top of the level meter. With this in mind, lets take a moment to explore what clipping really means.

Controlling Clipping

Clipping occurs when too much signal is fed through a channel. Clipped audio sounds fuzzy and distortedyou certainly don't want clipped audio in your song. Fortunately, you don't have to rely on your ears alone. All audio channels have a clip detector that shows you when the channel is in danger of clipping.

The clip detector is above an audio channel's level meter. When too much signal is fed into the channel, this detector turns red to tell you that it's time to turn down the volume. Furthermore, once a channel clips, the clip detector stays on until you turn it off by clicking anywhere on the channel's level meter.

Because Logic uses 32-bit floating-point processing for all internal calculations, you can actually clip Logic's internal audio channels a little bit without creating distortion in your final mix. However, as soon as the audio leaves Logic through an output channel, you must be sure it peaks no higher than 0 dB. This is a very important concept, so let's create an output track in the Arrange window and use that channel to explore clipping.

1.

Open the file named 09Begin.lso, or continue working on your song from the previous lesson.

2.

If you do not have an empty track at the bottom of the Arrange window, create one now.

3.

Click and hold the empty track's name.

A hierarchical channel-selection menu appears.

4.

Choose Audio > Audio Output Stereo > Out 1-2.

The track updates to say Out 1-2, and the Arrange channel strip now displays the channel strip for Stereo Output 1-2 (the first Stereo Output on your sound card). Now the channel's level meter displays the level of the signal as it leaves Logic.

All of Logic's audio is currently being sent to Stereo Output 1-2, so in essence this channel acts as a master fader for your song. It is very important that you don't clip this output; should this happen, your song will sound bad. Period. But don't trust metrust your ears.

5.

Decrease your computer's volume.

You are about to massively increase the volume coming out of Logic. Protect yourself and your equipment by turning down the volume on your computer!

6.

To get a good, strong signal to work with, create a four-bar Cycle range that spans all the sounds in your song.

7.

Press the spacebar to play the cycle.

8.

With the Out 1-2 track still selected in the Arrange window, drag the channel strip's volume slider to the top (+6.0).

As the song plays, watch the Output 1-2 level meter and notice how it peaks past the top of the scale. If you listen closely, you'll hear distortion in your audio each time the level meter spikes past its top. (If you don't hear distortion now, trust me, you will in the final bounced file). This is clipping.

9.

Stop playback.

10.

Click the clip detector.

The clip detector turns off, and the red light disappears.

NOTE

If an audio channel clips, the clip detector remains on until you manually turn it off.


Reverting a Slider to Its Default Setting

The Out 1-2 channel strip's volume level is set to +6. Let's revert it to 0 using a handy trick: In Logic, Option-clicking a slider or a knob always returns it to its default setting. This works not only for the channel strip, but also for all Audio Instrument and effects plug-ins.

  1. Option-click the Out 1-2 channel's volume slider.

    The slider returns to 0, the default setting.

Adjusting Volume Levels

Under normal conditions the clip detector is off, and the numerical value it displays shows you the amount of headroom left above the channel's most recent volume peak. Headroom means the number of dB left before the channel clips. For example, if the clip detector is off (the background is brown), and the number it displays is 4.9, the channel can be raised a maximum of 4.9 dB before the audio clips. As you saw in the last exercise, when the clip detector turns red, the channel's audio has clipped, exceeding 0 dB. In this situation, the number printed in the clip detector shows you the number of dB over 0 at which the channel has peaked, which in turn is exactly the number of dB by which the track needs to be attenuated, or reduced, in order to avoid clipping.

Let's use the Out 1-2 channel's level meter to adjust the volume of the Output 1-2 Object so that it comes as close as possible to 0 dB without clipping the channel.

1.

Play the cycle and watch the clip detector to determine its maximum value.

In the figure above, the channel clips by 3.6 dB. Consequently, the channel's volume must be lowered 3.6 dB to avoid clipping.

NOTE

The fader values given in this exercise are all approximations and may vary from the values you need to use to achieve the intended result, given the Apple Loops you added to your song in Lesson 5, "Working with Apple Loops."

2.

Click the clip indicator to turn it off.

3.

Decrease the Output 1-2 Object's fader by the amount of dB needed to avoid clipping (for the song pictured, that is 3.6 dB).

4.

Press the spacebar to start playback.

In the figure above, a volume slider setting of 3.6 causes the song to peak at 0 dB. That's as loud as the song can get without clipping the channel.

TIP

By default, level meters show a channel's volume as adjusted by the fader. If you'd like to see the volume of a channel's source signal, choose Audio > Pre-Fader Metering (Logic Pro only).

5.

Press the spacebar to stop playback.



    Apple Pro Training Series Logic Pro 7 and Logic Express 7
    Apple Pro Training Series: Logic Pro 7 and Logic Express 7
    ISBN: 032125614X
    EAN: 2147483647
    Year: 2005
    Pages: 197
    Authors: Martin Sitter

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