Music Technology Lab
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Tutorial VIII: CD Mastering

This tutorial will guide you through some of the techniques used for Mastering audio.

There is no way to instruct any one person in the exact art of Mastering. The settings used in each session will probably be different (The settings used for classical pianist's concert will be different from those used for a jazz band concert).

With your ProTools session open, select "New Track" from the File pull down menu. Your session can have any number of tracks in it. Create a new Master Fader. This fader will mix all tracks in your session down to the standard 2 channel stereo.

You will now see a new track appear in the Edit and Mix windows. Audio cannot be placed in this track, but its volume and pan can be changed using the standard controls.

In the mix window, drag the Master Fader to the position where you'd like it to be. At the top there is an area with 5 boxes. These boxes are spaces for "inserts", used for effects and mastering tools. The software that drives these inserts are commonly referred to as "plug-ins".

To add a plug-in:

Click on the insert box
Select TDM plug-in (the first one after 'no insert')
A huge list will appear. When mastering, you can make use of many of these.

There are 3 plug-ins that we will be using. These are by no means the only plug-ins that can be used in mastering, but they are a good place to start. The first is called Drawmer GCLs (stereo). Select this from the list, and the insert will appear.

The Drawmer GCL is a combination Gate, Compressor, and Limiter. We will be primarily concerned with this plug-in's Compressor functions.

What is a Compressor?( from http://www.tangible-technology.com/audiobasics/basic_1.html)
A "compressor/limiter" is a device which acts as an automatic volume control (AVC). An AVC can optimize audio volume so that a weak signal is made louder and a loud signal is made softer.

Below are several pictures of the Drawmer plug-in. When you first enter this screen, notice the Bypass button under Noise Gate, on the right side of the plug-in display. Make sure this switch is down, in the "bypass" mode.

You will mostly be dealing with Threshold, Ratio, and Gain. Below are three examples of what the compressor does to audio.

	Too Much Compression Click to Listen Note the extreme settings of the threshold and ratio. Listen to hear the result of these extreme settings.
	Too Little Compression Click to Listen Note the setting of the threshold. This value may be OK for some applications, but for this particular audio, the threshold is set too high. When this setting is too high, the compressor never kicks in, leaving your audio untouched. This audio exerpt might as well have not had any compression on it at all.
	Good Compressor Settings Click to Listen

The next plug-in you'll add is a Q10 EQ (stereo).

To the right is an example of what the EQ plug-in looks like.

The EQ curve has 10 crosshairs that you can move to adjust the curve. You must turn each of these points on in order to apply that point to the curve. Not all points must be used. If you're not using all 10 points on the Q10, you can use a Q4 (which only has 4 points).

Press the On button right next to the Curve Type.

You will probably not need to use all 10 points in a Q10 EQ to effectively EQ a given concert.

Some EQ Tips:

Place a sharp rolloff in the curve at 60Hz. Frequencies below 60 can muddy up certain types of recording, particularly ones made in concert halls.
Place a small bump at 100Hz. This gives a 'false' sense of bass response on smaller speakers and car stereos.
Place a small bump at 3kHz. The human ear apparently finds frequencies between 2.9 and 3.2 kHz "pleasing".
Use Your Ears. If it sounds bad to you, don't do it!

Below are two examples of EQ settings:

	Poor EQ Click to Listen Note the relatively ridiculous shape of this EQ curve. While this may be useful for creative applications like computer music or sound sculptures, it's not very useful for EQing concert recordings.
	Good EQ Click to Listen Note that this EQ curve is nice and smooth, makes small stereo separations, and has rolloffs in appropriate places.

The final plug-in that you will add is called +L1 Ultmax (stereo). This plug-in will help keep the audio from clipping (acting as a Peak Limiter) and bring the overall volume up to a good listening level (acting as a sort of Leveling Amplifier).

There are three settings on the right side under IDR. Click on the boxes to change the settings to:

Quantize : 16 bits
Dither : Type 1
Shaping: Moderate

(to read more about these digital audio operations, read this.)

Setting the Threshold

Click and hold on one of the triangles in between the two peak meter bars.
As you bring them down, the audio gets louder.
The triangles should be brought down to about the highest level of the peak meters

Setting the Out Ceiling

Bring down the triangles between the peak meters one notch to -0.1
This will prevent some clipping (if there is any).
Note: This will not get rid of any clipping from the actual recording. If the recording clipped, that is, if there are digital clips on your DAT or DA-88 tape, other measures must be taken which are beyond the scope of this article.

	Poor Limiter Settings Click to Listen
	Good Limiter Settings Click to Listen

When we speak of recordings that are "Mono", we usually mean there is only a single channel used for the recording. Since human hearing is very directional, one-channel recordings lack the depth and width that can be achieved using two channels.
It is possible to add some false stereo (two-channel) imaging to repair a recording where one channel is damaged, or to make monophonic recordings sound broader.

Click to Listen to a sample of a straight monophonic recording.

Click to Listen to that same recording, with a little stereophonic reverb applied to it. This is by no means as good as a true stereo recording, but can add some depth to otherwise bare audio.

If the panning was done incorrectly, or one mic was hotter (level was higher) than another, the audio may sound unbalanced. Click here to listen to an unbalanced recording.

How to fix an unbalanced recording:
If one mic was hotter than another, your waveforms may appear in ProTools like the diagram to the left. In order to correct this, you can do one of two things:

Adjust the volume level on the each track to balance out the audio.

In the edit window, on each of the tracks, click on waveform. Then select volume.
Using the Hand tool, you can now adjust the volume.

Adjust the gain on one of the tracks to make it louder or softer.

Select the track (or portion of the track) you wish to change.
From the AudioSuite menu, select gain.
You can adjust the gain, +dB or -dB, and then press process.