Ellard

Much as I love to laugh at people all day, let’s use this blog for something useful.

Most people have a general idea about frequencies of sounds. They know that some sounds are ‘low’, ‘deep’ and some are ‘mid’ and some are ‘high pitched’. When they come to mix music they know that different instruments can be used together when they don’t overlap too much in frequency. They know an orchestra is designed so that different instrument groups such as horns and strings don’t compete with each other. That’s absolutely right, but it’s just the starting point of understanding how a music mix works. We can improve our music recordings greatly by a finer understanding of frequency.

When mixing I like to use a diagram. It has the Y axis, the one that points up the page as the frequency. The X axis, the horizontal one, is the panning across the stereo field. Implied here is a Z axis, which would extend ‘into’ the paper, of time. Our diagram is a slice through a changing pattern across the X and Y axes. We’ll not worry about the Z, but might have to draw more than one diagram per song.

If the sound is ‘low’ in frequency, it goes at the bottom of the diagram. A kick drum for example, goes roughly at the bottom. Hi hats go up the top. The way frequency works is such that as we go up the Y axis the frequency scale ‘speeds up’ logarithmically. There’s more change at the top than the bottom. Not too complex so far.

Each sound has a fundamental note, the basic tone of the sound. Above it come a set of overtones that give the sound a timbre. The tone of an electric piano has (ignoring some detail) few overtones above the fundamental, it’s ’round’ or ‘soft’. The scrape of a violin has many more overtones and is ‘sharper’. A gong has many overtones which are inharmonious with the fundamental tone. A cymbal, which is a type of gong, has so many overtones it makes a sizzling sound.

So in our diagram, we can’t place the instruments in one place, rather they cover an area of the frequency range. And it’s those areas that can overlap. If your kick drum has overtones that extend into the region taken up by a bass guitar, they may be masked by the bass, making the kick sound less rich. This is a reason why a mix can sound muddy. But there’s more.

While synthetic instruments may have one fundamental sound, very rarely do real instruments occupy just one area of the frequency spectrum. They have at least two and often more sounds that combine to give them their identity. For the purposes of our discussion here, let’s use the term ‘sound’ for one component in an ‘instrument’.

Draw a picture of a snare drum. There’s the skin at the top. There’s the drum. There’s the snares under the drum that rattle. That’s three sounds in one instrument. When we place that snare in our mix diagram it’s going to take up multiple spots. The drum will ring somewhere around the middle, an area that we can roughly identify as the ‘vocal’ range. That ring is a tone with mostly harmonic overtones. The whack of the stick on the skin is somewhat higher up. Even higher is the rattle of the snares. All three are now taking up space. When a recording engineer uses a microphone above or below (or both) a snare, she’s trying to accent one of these multiple sounds so that the mix can choose between them.

A kick drum has a skin and a drum but no snares. It has the boom of the drum which is a very deep note, also the thwack of the pedal hitting the skin. All instruments use up multiple areas of the frequency domain. So when somebody says an instrument is ‘at’ a certain frequency they’re simplifying.

EQ works in accenting or reducing overtones in the sounds that make up an instrument. Rolling off the top end of a kick drum removes the pedal sound, then as we go down, the drum becomes less sharp. Rolling off the bottom end we lose the boom of the drum first and eventually hear only the impact of the pedal. We can also ‘notch’ a frequency to remove a particular sound from an instrument.

So how does knowing this help mixing? For now I’ll do an executive summary, then later we can go into the specifics.

We can write music that doesn’t try to have similar instruments playing at once. e.g. Write bass notes that don’t sit on the kick, but oppose it or anticipate it.

We can also write it so that more instruments join in later and our memory of what went before gives the impression that we still hear the earlier instruments clearly. The sound can drop out to remind the listener of what was concealed.

We can move instruments out of each others way by either choosing them wisely (bass, guitar, drums, but no flugelhorn), recording them to occupy different frequency spaces, or using EQ to do the same thing. The reason that rock bands tend to play a fixed set of instruments reflects years of experience. Also a guitarist knows to switch models so as to shift his timbre out of the way of other instruments. As a recording engineer you should be listening to sounds for their timbres and trying out EQ to change these in a reproducible way. We’ll talk about EQ more later.

More advanced, we can remove a specific area of frequency from one instrument that was masked by a another. When two sounds try to occupy the one space, they might add together, but they can also subtract from each other if they are out of phase, again explained later. Usually we get ever changing phasing that causes that frequency to oscillate unpleasantly. When we remove that frequency from an instrument (by for example not using the ring of a snare) we get a cleaner sound. The listener doesn’t notice the missing frequency because they hear it covered by other instrument.

We can move sounds into different areas of the stereo field. Drums in the middle, guitars at sides. There’s all kinds of rules here that we will come back to. Let’s just say that the ears are assisted greatly by having sounds come from different origins. We’re built to discern from where a sound comes, and so the frequencies untangle as they move across the X axis.

We can accent parts of the instrument, for example place a microphone so that the slap of a bass is louder than the bass body, or use compression with an attack so that the slap is made louder, and more on compression later.

We can add overtones to a sound by using overdrives. That’s what a lead guitar does to stand out. When ‘industrial’ bands use distortion on every instrument, they wonder why it ends up sounding dull – simply because again everything is overlapping.

We have quite a few things to cover just on this idea and for that reason we’ll meet again in the next installment. Anything tagged in the blog as ‘music class’ will be useful. Anything else you can be sure is rubbish.