Tech Notes: Mastering

A friend of mine was asking me about mastering recently, specifically whether I master my tracks or not, so I explained my methods to him. It occurred to me it might make an interesting blog post.

What is mastering? Essentially it's the final step in preparing audio for the listener's ears. Generally it means taking a finished song and running it through EQ and compression so that it sounds big and beefy like you expect a song to sound on the radio. Now, I have a huge problem with how popular music is mastered these days, so the mastering I apply to my music is minimal at best. I make sure the EQ is how I want it at the mixing stage, and apply only enough compression to the final mixdown to ensure that the overall loudness of each track is roughly the same. No fancy squeezing of the bass, expanding of the mid-range, or sharpening of the high end that could give you papercuts.

When a multi-track mix is finished, the first thing I do is play it back with the VU meter running, so that I can see whether or not the output is clipping. I touched on clipping in another post, but essentially it means audio is going 'into the red' and being cut off (or 'clipped') from the output stereo audio file. If this is happening, the VU meter will tell me exactly how much audio is going above the cutoff point, and I can drag the faders down to compensate. The end result is a clean file with all the audio information present, but a much lower volume than intended. I refer to this as the 'pre-master.'

The pre-master is then loaded into my audio editing program of choice: Sound Forge XP. The first thing I'll do is open the Normalize dialogue and run a scan for two things: the maximum peak level of the audio, and the RMS (overall loudness). If I've done my job correctly, the peak level will be somewhere below 0db (maximum). The RMS will vary depending on how much I've had to lower the volume of the track. It's generally somewhere in the region of -20 to -15db.

Sound Forge: the normalize dialogue box. Note peak level and RMS.

This is the waveform representation of a pre-master from a forthcoming e.p. Note the peaks are not touching the edges of the box. This is good - it means it isn't clipping.

Waveform: pre-master.

The RMS isn't always a reliable way of determining how loud I want the finished track to sound. If a song has no drums, for example, the RMS will come out wildly different compared to one that has. From research and trial-and-error I've determined that an RMS of -15db is a comfortable level for my music. Sometimes this varies from track to track by a factor of up to 5db. Ultimately I rely on my ears for the final judgement.

In order to bump the volume back up to where it should be, without the audio clipping, a compressor is required. This is a bit of software (or hardware) that determines which parts of the audio are clipping when you turn it up, and smooths them out instead of cutting them off drastically like a pair of scissors. The result is much more pleasing to the ear, but care must still be taken not to use too much compression, otherwise your audio will end up sounding like a Ricky Martin record (gasp!), and the waveform will look like a solid blue line, instead of a nice centipede shape.

Sound Forge has several compressor plugins, and they can be puzzling to work with if you don't know the first thing about them. I rely on the tried and true Wave Hammer compressor. Here's a picture of the dialogue box and the preset I use, called 'Master for 16-bit,' which takes all the guesswork out of it.

Wave Hammer: Master for 16-bit.

Inasmuch as I understand it, the first slider is the threshold, or the part of the waveform the compressor is going to lift up by its boot-strings. The second slider is how much attenuation, or squashing, of the peaks is going to occcur. The third is for the overall volume you wish to apply to the track beyond initial compression. If, for example, I've had to pull the volume down severely on the pre-master, I'll experiment with the output gain until I get back at least the amount of volume I took away in the first place.

Waveform: mastered version.

Here is the mastered waveform. You can see it's considerably fatter than the original (by a factor of 5db to be exact), yet you can still see the gaps between peaks: the mark of a successful operation!

Once this is done and I'm happy with the final result, I normalize to 98% (this is just a personal preference, and brings any peaks hitting -0db down to -0.02), and apply fade-ins or -outs if needed. I might also add silence to the end of the track if I think it leads into the next one too soon. Oftentimes I'll have to make adjustments or master a track from scratch if I've got something wrong in the mix, so I've taken to making notes of just how much compression I apply and any other edits I make after the fact.

And there you have it: how a Manitou record is prepared for consumption without making anyone's ears bleed or speakers explode.