Mastering

Step 1: Mix it the best you can

Mastering is the final stage in audio production, where the entire mix-down is processed at once. It's important that you don't expect too much from this stage. Make the mix sound as good as possible before the mastering stage. Mastering should be used to fine-tune and polish the overall sound, not to try and fix glaring problems within the mix. Make sure that your mix-down doesn't clip and that you leave some head room (~3-4db) for effects such as EQ.

Here's my unmastered mix-down:

Step 2: Listening, comparing

Make sure you are in a good quality listening environment (with half-decent speakers) that you are used to. Listen to several different well produced tracks that are of similar style to your own. It is important that you get a good perspective of your mix, since listening to it for hours can warp your perception.

Step 3: EQ

Most mixing software comes with a reasonable EQ built in, or alternatively you can get hold of a good parametric EQ plugin. Listen to your track and compare it to other similar tracks (through the same speakers). To listen at the same volume, you will need to turn down the comercial tracks you compare it to (to about the same loudness as your own), as these have already been compressed. It's a good idea to listen at different volumes. Turning the volume up often reveals if there's too much bass. If anything is clearly wrong (too much bass, too much treble) tweak it here - try to keep a smooth curve to your EQ. Don't use narrow notches without knowing exactly what you're doing. Keep comparing while tweaking, until you get the overall balance right. You are not trying to match the exact same EQ as your reference track, as there are probably different sounds involved even in very similar tracks (different distortions, cymbals, vocals) - different sounds are different frequencies. So don't get carried away trying to make an exact match, as an exact match will probably make your mix sound worse. It can be done with tools such as Har-Bal, and it doesn't sound good. Make sure that when you apply the EQ you don't cause the signal to clip.

For my EQ I used Izotope Ozone's paragraphic equalizer, with the following setting:

The result is fairly subtle change, as mentioned before; mastering should be about polishing a good mix, not having to make drastic changes.

Step 4: FX?

Here are some commonly used mastering effects which I generally avoid, but you will probably want to try out at some stage:

• Harmonic exciters - Harmonic exciters artificially generate frequencies. They can be used to "fill-out" the signal. Personally I prefer to keep the signal clean rather than add noise to it to fatten it up. They can be useful on certain material.
• Stereo width enhancements - Stereo width or "image" expansion increases the difference between the channels, making the sound wider. I sometimes use these on certain tracks in a mix, but never on an entire mix. I believe the stereo image should be dealt with before mastering, by tweaking the individual tracks - this way you can isolate the parts you want to widen. Stereo expanders should be used carefuly, as they can ruin a sound when it is heard in mono - for example if you have two speakers close together, and listen from the opposite corner of a large room.
• Mastering reverb - Mastering reverb is generally used to make a dry mix sound smoother and less "in your face". Again, I prefer to add reverb to my individual tracks before mix-down.

Step 5: Compression

Most commercial recordings are heavily compressed in order to compete in the "loudness wars". The idea is that louder records have more impact. Often a lot of quality is lost in order to make a recording loud. If you want the best quality sound, it's best to avoid this alltogether. Unfortunately this would probably leave people having to turn up their volume for your track, or thinking the track is weak sounding.

There are different ways to compress the final mix:

Mastering Limiters

In limitation, the signal is limited so that it won't clip past 0db. The signal can be heavily gained, but (depending on the limiter) all frequencies can be retained. As the gain is increased too much, the signal starts to distort - somewhat differently to clipping.

Clipping

Some mastering engineers prefer to just clip the signal to increase loudness. At the point the signal clips, the natural curve of the wave is lost and some higher frequencies are flattened. Some argue that the clipping only affects a small fraction of the overall signal. With this method I generally find that the signal sounds the same to a point, then I start to hear distortion and artifacts. Clipping usually retains the attack of the snare drum, which is often lost with mastering limiters set on slower attack settings.

This image shows how clipping loses some higher frequencies within the wave, and limiting retains these frequencies while increasing the rest of the wave's amplitude by the same amount.

For this example, I used Isotope Ozone's "Loudness Maximizer". I set it to "intelligent" mode (it handles the release for you) and set the speed to 0.6. I used a threshold of -7.8db, which brought my mix up to commercial volume levels - too loud.

Recommended mastering tools

• Isotope Ozone - Complete mastering suite including a parametric equaliser, multiband dynamics, multiband stereo imaging, mastering reverb, multiband harmonic exciter, and a loudness maximizer.
• Waves L2 - Well known mastering limiter. Notorious for it's missuse, but decent if used tastefully on the right material.
• Voxengo Elephant - A good and well priced mastering limiter.

• G-clip - Clipping tool with rounding and 2x upsampling. Rounding gives the clipped waveform a more natural curve, resulting in slightly less noticable distortion.
• TLS Pocket limiter - A great free mastering limiter.

General Tips

If it ain't broke, don't fix it. It's easy to get carried away, hearing improvements to the sound that aren't actually there. There can be a psychological effect of adding certain effects, you may think you're making improvements when you're actually making things worse. It's good to keep checking your master against the original to make sure it sounds better, and that you're not losing perspective.