Equalization – sculpting sound
Equalization is called EQ for short. Equalization effects timbre (the harmonics of an instrument) and is related to the filters used in subtractive synthesis.
EQ was originally used to balance the tone or entire sound spectrum of a recording, mostly on a playback system instead of in the recording stage. One use of an equalizer is to balance or equalize the sound. A Graphic EQ is usually used for this purpose. As EQ’s evolved, EQ has changed to allow a user to sculpt the frequency spectrum of a single sound. This sculpting is usually done with a Parametric EQ.
The most popular equalizer type for mixing is the parametric EQ. It usually has four bands: Low, Low-mid, Mid-high and High. Each band has a sweepable frequency. The high and low are usually switchable between band and shelving curves. Shelving curves are identical to high-pass and low-pass filters of subtractive synthesis. The exception is that EQ shelves, unlike HPFs and LPFs, are usually static where the cutoff frequency is not changed over time.
Parametric EQ is popular in the recording and mixing stage of music production because it can dial in any frequency with any curve.
EQ Frequency Spectrum:
LO: 20 Hz – 100 Hz
Felt more than heard
Too much EQ in this range can “muddy” a mix. Too little can make a mix sound thin.
LO-MID: 150 Hz – 800 Hz
The fundamental of almost all instruments is in this frequency range. As such, it is where all the “musical” content is.
Bass Guitar – body of the sound
Guitar – body of the sound
Too much EQ in this range can sound honky. Too little can make a mix sound lifeless, as this is where all the fundamentals are.
MID-HI: 800 Hz – 8000 Hz
Electric Guitar edge
Too much EQ in this range can sound nasally. Too little can make a mix sound unfocused and lacking definition.
HI: 8000 Hz – 20000 Hz
This is the “sizzle” range of a mix.
Too much in this range causes ear fatigue and makes a mix sound harsh. Too little in this range makes a mix sound dull and masked.
Cymbals are in this range.
General Principles when applying EQ
- It is better to remove frequency than to add
- Avoid 6 dB or more changes unless you know what you are doing
- Enhance what is pleasing in a sound
- Remove what is unpleasant or unnecessary in a sound
Examples of removing unnecessary timbres with EQ would include bass roll-offs for vocals and guitars if there were other bass instruments such as bass drum and bass guitar that can fill these sonic spaces.
Linear Phase EQ
What is “linear phase” equalization? Very few equalizers behave in a manner that does not interfere with the phasing of a signal. A few high quality digital equalizers can maintain the phase integrity of a signal while applying EQ changes. The tradeoff is latency. TC Electronic’s Dynamic EQ for their Powercore card is an example of a Linear Phase EQ. Logic Pro also has a linear phase EQ. Linear Phase EQ is used mostly in mastering to preserve the phase integrity of the signal while processing.
Q: What is Phase?
A: Phase is where a waveform is in its cycle relative to the start of the waveform or another waveform. A sine wave, for example, that begins cresting before completing a cycle by troughing is in-phase or 0 degrees in phase. If the same waveform started at the halfway point or at the troughing section of the waveform it would be 180 degrees out of phase with original. If two identical waveforms are 180 degrees out of phase at the same amplitude, the waveforms cancel each other out. Think of it like this: One waveform is trying to push the speaker out with the exact same pressure that another waveform is trying to pull the speaker in with. The result is no movement of the speaker thus a canceling of the two sounds.
EQ’s introduce phase problems unless they are well designed. Phase problems are rarely such that two waveforms are 180 degrees out of phase. Partial phase cancelation can occur in the harmonic content of sounds and this can shift as two instruments or sounds change the notes that they are playing. Phasing problems are most likely to happen at the recording stage when microphones are improperly placed. Phasing can be electrical or acoustical, but this is beyond the scope of this resource.
What you really need to know about phase is this: Extreme use of EQ introduces phasing problems and perhaps that the snare drum and overheads are the most likely tracks to have acoustical phase relationship problems.
Q or Bandwidth
Q or Bandwidth – How broad or narrow in the frequency spectrum the EQ effects the sound.
Frequency – The centre frequency of the EQ.
Gain – How much boast or reduction is applied to the specific frequency.
Complementary EQ occurs when two instruments of similar frequency range are EQ’d differently so that the two instruments are no longer harmonically emphasized in the same frequency range.
Mastering EQ is the EQ that is put on the finished mixes before they are sent to be duplicated or broadcast. Mastering EQ is the last chance to fix the balance of the frequency spectrum before the mix is released. Mastering EQ is usually subtle with adjustments of less than 3 dB and rarely using steep slopes unless there are sonic problems that need to be addressed.