How To Use A Spectrum Analyzer (And How Not To)

A spectrum analyzer is a bit of a double-edged sword.

While learning to use them you might discover certain “truths”, only to realize later that the same “truth” just ruined your mix. I’ve certainly had my ups and downs with them, but I’ve come to appreciate what they can do, and when it is better to simply ignore them.

My analyser of choice is Voxengo SPAN. I like it because it’s usable, and it’s free. If you want to jump right in, you can download my Span preset Download my Span preset.

First, let’s set it up right. I find a window size of 8k samples suitable. This gives adequate resolution in the lower frequencies. I then set the AVG time knob to around 200ms which allows me to comfortably follow the movement of the display. I also set the metering to “k-20” as this represents the levels I mix at. Finally I add a second spectrum that holds the peaks behind the moving spectrum. It can be reset by clicking the display.

Frequency spectrum analyzers give a very technical representation of a sound, and, much simplified, all they show is the volume level of a particular frequency at any given moment in time. As such I’ve found their functionality to also be technical, rather than musical.

For one, they are great at showing you how low in frequency a sound actually goes. In many cases sounds will have energy in the low octaves that simply isn’t required. In fact, retaining this low frequency rumble will eat up space in our low end that our kick and bass could occupy, thereby reducing their punch and definition.

Snares are often candidates with unnecessary rumble. Solo your snare and look to see if the spectrum analyzer shows any movement below about 150Hz. Chances are you won’t need that energy. Similarly, low bass notes often extend way below 50Hz, especially from synthesizers. Since most sound systems can’t reproduce these frequencies anyway, it’s pretty safe to remove them.
Spectrum analyzers are also great for spotting ugly resonances in a sound. Where these come from will most often remain a mystery, yet they are easily visible as peaks on the display that are substantially higher than the peaks around it. Reducing or completely removing them often triggers a strong “ahhaaa” effect, making the sound more open, comfortable and simply less annoying. Untamed resonances can wreak havoc on all sorts of sound processors and the oh so important balance question.

The final use I have for the spectrum analyzer is much more a musical one than the first two and thus needs to be exercised with caution. That is re-balancing individual harmonics of a sound. While the goal here is completely dependent on the particular scenario as well as your taste and I therefore I can’t recommend what you should do, it is quite possible to use the spectrum analyzer to see how the individual harmonics in a sound are balanced against each other. Sometimes an instrument somehow feels uncomfortable or is difficult to mix because a particular harmonic is to loud, or the balance of harmonics is otherwise unfavorable. Dipping or boosting certain harmonics with an EQ can then be used to great effect.

The one point I’d be very careful with is judging the quality of your mix by its overall frequency balance in the spectrum analyzer. A great mix is one that supports the emotional statement of a song in the most effective manner. For one, this says nothing about the actual sound quality of the mix, but more importantly it certainly doesn’t say anything about its frequency balance. Everything is allowed and nothing is forbidden, as long as it triggers the right emotions. It is sometimes mentioned that you should aim for a “flat” frequency balance but, while some great mixes do in fact exhibit this behavior, it is by no means a hard-and-fast rule. In any case, mixing such that the spectrum analyzer shows a “flat” response will most likely not be the right frequency balance for your song.