Audio Recording Issues – Actual notes that are out of balance Part 1Not everyone is aware that Equalizers can be used to affect the actual notes of an instrument, and not just the tone, hum, or noise of a track. The notes of a scale all have an equivalent Frequency range. This idea is similar to the way that radio Frequencies are transmitted. Each individual Frequency represents a sound that is a separate pitch from all other Frequencies.
With a wide "Q", meaning that the shape of the EQ starts at a center Frequency and extends a large amount below and above the given Frequency, an EQ will usually cover overlapping notes in a scale. But, with a narrow "Q", you can focus in on a single note. It is not as easy as literally manipulating each individual note on a track or an instrument in a mix. Musical notes are expressed in complex combinations, each of which is completely unique to the instrument being played. We can express a note in terms of attack, swell, sustain, decay, and many other expressions. A note with a fast attack may start with an articulated pitch and, if left to sustain, may resolve to a steady tone that is more accurate to the note played, depending on the instrument. The note itself can carry multiple overtones that are expressed as harmonics. These fluctuate with the instrument, materials, performance, and sustain and attack factors as well. The way that a note is played therefore affects how much we hear of the primary note and its harmonics, and whether there is natural fluctuation in this combination. A note from an instrument usually also carries natural ambient sound from the instrument itself, along with its environment. Even in close, direct miking, we hear things like the vibration of a wood cavity on an acoustic guitar or the hum of a string. With information coming in from anywhere a waveform can travel and bounce off of a surface, it presents a new complex abstraction of the original note.
With rooms, the note can become more scattered, with the timing spread all over the environment, and the actual sonic qualities of the room itself can stray from the primary root note. These are just a few of the factors that can affect the use of Equalizers, so you should always listen for the qualities that accompany a note and performance when making a corrective adjustment. What do you do if you have a final mix that is ready to send to the Mastering Engineer, who notices that the bass player had a couple of strings out of tune? Your song has already been mixed down and everything sounds great. But, you didn't really notice that there were a few sagging notes coming from the bass guitar. It is possible to sweep a narrow EQ and isolate the offending note, or notes.
There are many options for this scenario. Since the song is mixed, you are not likely to make a pitch adjustment that doesn't affect the other instruments in the mix, and this can be damaging to ambient sound and stereo detail to the rest of the mix as well. But, you can lessen the blow by gently reducing the volume of the offending notes. Sweep the Frequency of your narrow band EQ, place a limiter on the end of your mastering chain, and boost the EQ so that it will resonate when it hits the note being played. You can use a low quality digital Equalizer for sweeping the signal, as it is easier to hear the resonance of a bad note with a straight forward EQ, where a high end EQ will resonate better and more subtly on the same note. When I work with a situation like this in mastering, I tend to use a basic digital EQ to find the note I want to reduce, and then I will switch to my "Mastering Suite" Nebula Pro narrow band EQ to reduce the signal by a few dB.
I only make the adjustment for the duration of the note at each passage, and only when it is the most obtrusive. This technique is even more effective when used for a note that is on the correct pitch, but is simply too loud. Once again, you don't want to upset the balance of things like ambient sound and other overlapping Frequency qualities, but if a certain note stands out it may affect the volume and balance of the entire track. The question becomes whether something else is prominent in the same range. Do you have a bass guitar note that is louder than the rest of the performance, but also have a kick drum that uses the same Frequency or pitch?
You may want to EQ only at certain passages or to use less dB reduction to avoid weakening the kick drum. What about ambient sound from a well-recorded guitar or other mix elements that share this part of the lower register? You don't want to harm the mix by trying to fix a single element within it. Another option is to identify the note or Frequency and also use a multi-band limiter to slightly compress and reduce the same Frequency. This is the idea behind using Equalizers to help deal with individual notes that are out of balance.